ASTR100 FALL 99 BULLETIN BOARD

MESSAGE #189. Thu Feb 3 19:51:40 2000 . Eric Webster wrote:

Hi Monique! I wonder if you are the only person who checks this board. It's kind of lonely here now; just me checking in every so often...

Katrina if you are out there, email me webster@wam... re phil170: I really would like your take on the class, and whether you think the winterterm was a goo time to take it, etc.

MESSAGE #188. Wed Dec 22 21:54:30. Eric Webster wrote:

See that Moon? Last full one of the 1000's, and it's pretty bright. NPR revised its estimate to the brightest in the last 69 years, not 133.

So what kind of Moon do the Shuttle crew fixing the Hubble see tonight? What kind of Earth? Don't forget, they're orbiting us once every ninety minutes!

A final word of THANKS to..

Katrina and Monique, lecture and homework buds. You guys made the pre-lecture time well-spent, productive, and entertaining. I'd love to share another class with you, but Philosophy? Chemistry? Uh-uh...

Dr. H -- Thanks for making some really challenging information accessible! Hey, now that I'm not in your lectures anymore, you can wear that pyjama-esque paisely shirt again!

If anyone is interested in joining me in commending Dr. H. to the dept & college, email me at _webster@wam.edu_ (just leave the underlines off the email address--prevents junk mail from arriving).

See you all around!

MESSAGE #187. Thu Dec 16 13:45:11. Prof. Doug Hamilton wrote:

Good Luck to everyone on the final!!!!!

MESSAGE #186. Thu Dec 16 13:44:37. Prof. Doug Hamilton wrote:

Thanks for the kind words Saadia-Yael!

This is it! My last chance to teach before the Millenium tolls! Most of you probably remember me jabbering about lunar and solar eclipses; well we will actually have a lunar eclipse in about a month! This is definitely an event that is worth watching from wherever you will be over the holidays.

For those of you that will be here, the Astronomy Department will be hosting an event for the lunar eclipse on Thursday, January 20th. We will be running our normal Open House event at the Observatory according to the usual schedule. From 10:00 pm to 1:30 am, portable telescopes will be set up in Hornbake Plaza. Totality for the eclipse is 11:04pm to 12:23am, Eastern Standard Time.

MESSAGE #185. Wed Dec 15 14:52:01. Saadia-Yael Eisenberg wrote:

I want to express my gratitude for this class, although its been a core requriement for me and not in my major field, nonetheless its been very exciting and informative. I certainly no longer look at the sky in the same way, nor do I think of the heavens in the same way. It is marvelous to think the astronomers of the world have these mathmatical progressions as their personal vocabulary with which to speak of distances, sizes, masses, escape velocities, etc., etc.and give us a conceptual imagery of the solar system, galxies, universe and beyond. Thank you Doc Hamilton for your tiger walking, brilliant lectures....be kind to "we scientific illiterates" on the exam!!!

MESSAGE #184. Tue Dec 14 23:41:25. Eric Webster wrote:

Possible Bonus Point Question on the Final:

the definition of a second: the duration of time it takes a cesium atom to resonate 9,192,631,770 times.

MESSAGE #183. Tue Dec 14 23:38:03. Eric Webster wrote:

>>Superfluous: more than what is necessary, or the number of messages Eric has >>posted on the Bulletin Board. :-)

Superfluous: the comments Eric makes on the message board -- like this one!

>> Wasn't the article from the URL you posted written about a new >> clock adapting to the Earth's rotation? I mean there's nothing much >> >> astronomers can do about Earth's rotation other than adapt to it...

Well, I really ought to have mentioned that I WAS KIDDING about astronomers 'sitting idly by'. We KNOW that astronomers are working hard to solve the imminent slowdown of the planet's rotation. [sic]

Actually the super-accurate clock (there was a guest lecture on time courtesy of Physics Dept today, but I missed it) needs to be ADJUSTED since the days are getting longer and longer. I think Earth slows by a second every 600,000 years or so. You need a timepiece a significantly more accurate than a Swatch to make that kind of observation.

>> Personally, I wouldn't welcome extra time in a day because it would just >> give professors an excuse to assign more homework. For every minute added to a >> day, I can picture professors adding an extra hour or so of work.

Aren't we here to learn? We should endeavor to understand all that the profs are trying to impart to us. I'm not satisfied with the dark matter 'answers', though.

MESSAGE #182. Tue Dec 14 20:12:52. Katrina Martinez wrote:

Superfluous: more than what is necessary, or the number of messages Eric has posted on the Bulletin Board. :-)

Eric--in response to your message in #179, I don't think astronomers are "sitting idly by," allowing the Earth's rotation to slow. Wasn't the article from the URL you posted written about a new clock adapting to the Earth's rotation? I mean there's nothing much astronomers can do about Earth's rotation other than adapt to it...unless you can think of something feasible. Also, the article says the Earth is slowing down "at a very slow rate," something we should be worried about, but not as much as the upcoming Astronomy final.

Personally, I wouldn't welcome extra time in a day because it would just give professors an excuse to assign more homework. For every minute added to a day, I can picture professors adding an extra hour or so of work.

MESSAGE #181. Tue Dec 14 14:03:47. Prof. Doug Hamilton wrote:

December 22, 1999 and the Moon - Mark your calendar!

This year will be the first full moon to occur on the winter solstice, December 22, commonly called the First Day of Winter, in 133 years. Since the full moon on the winter solstice will occur in conjunction with a lunar perigee, (the point in the moon's orbit that is closest to Earth) the moon will appear about 14 per cent larger than it does at apogee, (the point in its elliptical orbit that is farthest from the Earth). The Earth is also several million miles closer to the sun than in the summer, and sunlight striking the moon will be about 7 per cent stronger making it brighter. Also, this will be the closest perigee of the Moon of the year, since the moon's orbit is constantly deforming.

In layman's terms, it will be a super bright full moon, much more than the usual AND it hasn't happened this way for 133 years. If the weather is clear and there isn't a snow cover where you live, it is believed that even car headlights will be superfluous. (...get your dictionaries out.....) Our ancestors 133 years ago saw this. Our descendants 100 or so years from now will see this again.

Happy Holidays!

MESSAGE #180. Tue Dec 14 10:36:13. Prof. Doug Hamilton wrote:

Hey George,

I haven't forgotten your question! Enormous explosions in space (supernovas) do create black holes. But the material that falls into the black hole gets scrunched up and stored inside the black hole and the black hole becomes more massive. The black hole hoards its mass - it doesn't release material into another galaxy or universe as far as we know!

Eric - what's so bad about the day getting longer? Most people I know have too much to do in our current 24 hour day and would welcome a little extra time!

MESSAGE #179. Tue Dec 14 7:12:14. Eric Webster wrote:

As if the "big crunch" and the eventual transformation of the Sun into a red giant wasn't enough, now we learn the Earth's rotoation is slowing down!

How can astronomers sit idly by and ALLOW this to happen?

MESSAGE #178. Mon Dec 13 22:08:41. Eric Webster wrote:

Yeah I noticed the "earthshine" too. Better than tonight!

Didja see Mars just to the right of the Moon?

MESSAGE #177. Mon Dec 13 20:49:54. Ian Ullman wrote:

That crecent moon marked the start of the Muslim month of Ramadan and is the reason the crecent moon is a symbol of Islam.

MESSAGE #176. Mon Dec 13 18:19:22. Christina Roney wrote:

I check it! Mainly to see what kind of Astro-babble is going on. . . =) And who's checking in, and who's getting talked about. . . it's fun stuff. . . . Oh, and that cresent moon the other night was brilliant! It was the thinest I've seen it in awhile and you could see the rest of moon's outline around it too. Quite amazing.

MESSAGE #175. Mon Dec 13 17:38:33. Katrina Martinez wrote:

I check it every so often, but I wonder what that says about me...

One of the astronomers quoted in the article goes to the Max Planck Institute; isn't that where Dr. Hamilton did his postdoctorate?

MESSAGE #174. Mon Dec 13 17:22:49. Eric Webster wrote:

Article from CNN / Reuters on how planets may form in other solar systems

May Jupiter have possibly ejected a previous planet or two?

Of course, I bet noone checks this board, anymore..

MESSAGE #173. Sun Dec 12 17:39:16. Eric Webster wrote:

If anyone wants to help NASA find their stuff on Mars, you can see the planet pretty easily tonight (Sunday) just to the right of the crescent Moon tonight.

Does this mean we'll be seeing the 'pink planet'* in approximately the same position for the next few days?

Sniff.. one more lecture.. one more exam... no more homework.. boohoo, I can't stand it..

*it looks more pink than red to me!

MESSAGE #172. Fri Dec 10 0:23:09. Brandon Wise wrote:

If anyone is out there who could offer some help on ch.15 prob 2,3 and Ch 16 thought question 2 I would gladly have their baby. Well maybe not, but I would be grateful anyway. Thanks. either post a suggestion or e-mail me bwise@wam.umd.edu

MESSAGE #171. Thu Dec 9 17:16:36. George Morgan wrote:

Eh Prof. Hamilton, is it fair to say that an enormous explosion anywhere in space could cause a "tear" - a black hole? If this is so, where do all the matter go, into other galaxies? Oh and I heard the Mars mission failed for reasons like you said, the antennae was/is pointed in the wrong direction.

MESSAGE #170. Thu Dec 9 16:19:44. Eric Webster wrote:

Review Questions are not online, but there is (under homework & assignments on the ASTR100 Homepage) a Review Sheet that outlines what the test covers, which is pretty much everything we've studied. Charles' strategy for the review session is to go through each of the topics on that sheet as well as time will allow, and follow that up with a Q & A period. The second review was much more worthwhile than the first one, and if Charles keeps improving at the present rate, everyone attending the review this time should get an "A"!

MESSAGE #169. Thu Dec 9 15:49:45. Ihuarulam Ukeje-Eloagu wrote:

I just wanted to know which of the TA's will be conducting the review session next week? i have not been able to attend any of the sessions throughout the semester because of work and i just want to know how informative they are.

MESSAGE #168. Thu Dec 9 15:40:07. Ihuarulam Ukeje-Eloagu wrote:

Could someone help me out here? i was under the assumption that there were study questions on the class web page but i can't seem to find them. Is there a special way of getting the questions? Help me out people!

MESSAGE #167. Thu Dec 9 14:36:12. Prof. Doug Hamilton wrote:

Hmmm. Actually, I think we misidentified the nova. :(

It turns out that it has faded significantly and is now much harder to find. What I was looking at turns out to be a star ...

MESSAGE #166. Thu Dec 9 12:25:07. Olumuyiwa Lawal wrote:

Hey! Does anyone have any idea concerning when and where the final review session is going to be held in this class? Are all 3 T.A's going to be present or Mr.Greenwell is going to conduct it like the past 2 exams?

MESSAGE #165. Thu Dec 9 12:23:32. Olumuyiwa Lawal wrote:

Hey! Does anyone have any idea concerning when and where the final review session is going to be held in this class? Are all 3 T.A's going to be present or Mr.Greenwell is going to conduct it like the past 2 exams? thanks in advance !!

MESSAGE #164. Thu Dec 9 9:25:11. Prof. Doug Hamilton wrote:

Yo, Nova Hunters:

Using a pair of binoculars, I was able to spot the new nova from the Astronomy observatory last night! We couldn't see it without binoculars, but it is easy to pick out with them. The hardest part is figuring out which point of light is the nova. I'll bring my sky maps again on Friday if anyone is interested - they are very helpful!

Here's a quick sketch of what to do to find the nova. In the evening an hour or two after sunset, find a fairly dark place where lots of stars are visible. Spot Jupiter high in the sky and Saturn nearby and pat yourself on the back. Now comes the hard part. Look toward the direction of sunset and identify the summer triangle - a very large triangle formed from three of the brightest stars Vega, Altair, and Deneb. The star furthest from the other two is Altair. Now break out the binoculars and look at Altair. There is a pretty bright star next to Altair, visible in the same field of view of the binoculars. Draw an imaginary line between these two, and mark an imaginary spot midway between them. Now start from the imaginary spot and move the binoculars downward toward the horizon, in a direction perpendicular to the imaginary line between the two stars. Move the binoculars about three times the distance between the two stars. There are two more bright stars there (fainter than Altair and its friend though) - the brightest one ought to be centered in your binoculars. That's the nova! The nova looked distinctly red to me.

Let the class know if you are successful at finding it! Of course, you'll want to go back to that same part of the sky in a few weeks and see if the star is gone!

I also saw three of Jupiter's four Galilean satellites (Io and Europa were together and appeared as one object). Focus and steady the binoculars and you should be able to spot them as well. They are very close to Jupiter (Io, Europa, Ganymede, and Callisto are up to 3, 5, 8, and 13 Jupiter diameters out, respectively) and will all lie in a straight line.

MESSAGE #163. Thu Dec 9 7:13:47. Eric Webster wrote:

Did anybody catch NPR's piece on Wed. on the new information about the formation of the gas giant planets? My step-dad heard only the tail end of it, and my searches are (so far) coming up empty.

MESSAGE #162. Thu Dec 9 6:56:34. Eric Webster wrote:

Does anyone know where in the sky to look for the nova? If I can get a "between this star and that star", kind of answer, I should be able to find it from the CD that accompanies the book.

TIA

MESSAGE #161. Tue Dec 7 17:48:52. Katrina Martinez wrote:

Dear Ian,

Park's article does provide an interesting refutation to criticism of the "apparent" failure of the Mars mission. However, Park does exaggerate when he portrays criticism as people saying "the agency is mismanaged...the agency is incompetent...the agency should be killed." It may be effective for his audience, but it does little to strengthen his argument.

I personally have no problem with astronomy. I admire astronomers' curiosity in uncovering mysteries of the universe, uncovering truth no one else dares to seek. But you have to understand why people are angry. They pay taxes, money going to the government to fund programs like NASA. Of course they'd be angry if a mission failed: that's $165 million that could have gone to improving life here on Earth. Not that the money would have made much of a difference anyway; I suspect that one reason astronomy is so popular is that people are looking for new planets to colonize because we already screwed up life here on Earth.

Also, the last part of Park's article seems to be an argument against the space program. According to him, as we explore further the scale of the universe, we realize more how insignificant we are, how we are "fragile, self-replicating specks of matter, trapped on a tiny planet...in one of billions of galaxies." Why should we explore space further if the result will "diminish the specialness of Earth and its inhabitants?"

But that's no reason to stop exploring space. The goal of life, according to philosophers, is to uncover truth, one of the most painful aspects of life's journey. Of course it hurts to know we're not the center of the universe. But I think it's a little extreme to denigrate the human character as much as Park does, especially when it ends up hurting his argument.

In short: people aren't so quick to judge. They're angry, and justifiably so in some respects. But that doesn't mean we should stop the space program; it just means the more failures NASA has, the more it has to answer for.

MESSAGE #160. Tue Dec 7 9:43:06. Ian Ullman wrote:

The apparent failure of the recent Mars mission requires that one have some perspective. Luckily an op-ed article in today's New York Times does just that. And as a nice bonus it is written by UMCP professor (Robert L. Park). http://www.nytimes.com/yr/mo/day/oped/07park.html

Lets hope that those who are quick to judge read it.

MESSAGE #159. Mon Dec 6 22:23:10. Katrina Martinez wrote:

Gravitational constant G is 6.67 x 10^-11 m^3/(kg s^2) and can be found on p. 424.

MESSAGE #158. Mon Dec 6 21:48:09. Shan Hsiung wrote:

does anyone know what to use for G in the homework problems from chapter 15 i think it is? thanks!

MESSAGE #157. Mon Dec 6 21:32:13. Eric Webster wrote:

Hey while we're at it handing out accolades, how about a round of woo-hoo!s for Dr Hamilton for being good enough to provide us with this forum AND the ever-popular "What's My Grade Right Now?" calculator?

Woo-hoo!

MESSAGE #156. Mon Dec 6 18:58:26. Prof. Doug Hamilton wrote:

It is that time again, time for the coveted and world-famous ASTR100 Bulletin Board Awards! What awaits the lucky winners this year - fame? forture? public ridicule?

Our panel of judges are proud to present eight awards this year:

Most ranting message: Charles Greenwell (Msg. #153).
Angriest: April Jackson (Msg. #83)
Most apologetic: Eric Webster (Msgs. #85, #154).
Most chatty: Eric Webster (46 Msgs out of 154).
Chatty wanna be: Prof. Hamilton (22 Msgs).
Best vocabulary: Saadia-Yael Eisenberg (Msg #23).
Happiest: Imran Shaikh (Msgs. #35, #72)
Worst Paid TA: Eric Webster ($0 for answering lots and lots of Bulletin Board questions)

MESSAGE #155. Thu Dec 2 16:24:49. TA Charles Greenwell wrote:

I actually have been guzzling Mountain Dew, or even Jolt, like there's no tomorrow. Or more accurately, like there's no tonight. Not that it affects me; I can quit anytime I want.

I have a bit more faith behind the theories than most, but I definitely agree that they defy common sense. All I'm saying is that quite a bit about the universe actually does defy common sense. Something really weird should happen when you pile that much mass together, and a black hole is the weird thing that the theories currently predict. I never expect too much from my intuition; it's led me astray far too many times.

By the way, no self-respecting quantum mechanic would leave their oven on. The turkey might get burnt! I'd be more likely to skip dinner, in case a cooked turkey managed to appear in my stomach. Always consider the probability of a free meal.

MESSAGE #154. Wed Dec 1 21:33:57. Eric Webster wrote:

Who switched Charles' decaf soda with the real stuff? And he was showing such promise, tsk tsk.

I DO have a problem with relativity. If it's got mass, it's gotta have volume, right? At the beginning of the semsester it's like Newton's the greatest; by the end, Newton is hung out to dry on THEORIES.

My brother says that quantum physicists will turn the oven on with nothing in it, because there is a greater than zero probability that a turkey will appear fully cooked if he waits long enough!

Seriously, no offense Charles. You're a great TA, except for the Trekkie digressions..

MESSAGE #153. Wed Dec 1 18:25:14. TA Charles Greenwell wrote:

I am writing in response to the slander revealed in message 150. LIES!!! I do not know for certain which TA Mr. Webster refers to, of course, as it is quite possible that he is attending others' sections on the side. Assuming, however, that he is referring to me, I would like to state for the record that I have never "foisted" anything IN MY LIFE. I simply told my students to accept, without proof, a theory that may easily be incorrect and which I myself do not happen to fully understand. There's a world of difference.

I am trying to stem a horrible tide, Mr. Webster. You are bringing about the downfall of our education system. What would America be like if students arrogantly demanded proofs and reasons for what their instructors dictated? If they foolishly followed their own ideas rather than the ideas of others? I suppose that next you're going to claim that Newton was wrong about gravity, or that Einstein was wrong about quantum mechanics? You, sir, are leading others down the path to anti-intellectualism, and I for one will not stand by and watch you ruin others' faith in the infallibility of science!!!

MESSAGE #152. Wed Dec 1 13:53:41. Katrina Martinez wrote:

I'm sorry I missed Dr. Hamilton's Open House. I wish he had done it earlier in the semester so I could have gone. The Diamondback article is interesting; if you don't have a back issue, you can read it at http://www.inform.umd.edu/News/Diamondback/99-11-29/news3.html

MESSAGE #151. Mon Nov 29 20:17:48. Eric Webster wrote:

If you are interested in wowing yer pals (or winning wagers), you can pop the book's cd in the slot and enter the day of the year and your location, and it will spit out a custom star chart for you, including moon phases and planets and all the constellations visible from College Park (and quite a few that aren't). That way, you can approach your friends with, "hey, didja see Spica last night?"

Congratulations Dr Hamilton -- the Diamondback on Monday got some good sound bites from your Astronomy Open House!

MESSAGE #150. Mon Nov 29 20:09:43. Eric Webster wrote:

Black Holes --

Do they REALLY shrink down to a 'mathematical point', or are they just so dense that their escape velocity exceeds the speed of light? The book hems and haws, saying that black holes 'could be made of gerbils or corn flakes' and that we really don't know what exists in them and furthermore we can't know, by their definition.

While I reject the notion that gerbils or corn flakes are at the center of black holes (I may be going out on a limb here), I have difficulty conceiving of mass without ANY VOLUME whatsoever. The TA tried to foist some hypothetical wormhole proof on us, but I say whatever gets close enough to 'look' inside a black hole becomes "one with the void"!

Is it really the limit of our knowledge that we simply don't know what happens when gravity overcomes the neutrons' ability to pack together?

ps the book had a good density-of-a-neutron-star example: a teaspoon of one would weigh sixteen tons!

MESSAGE #149. Mon Nov 29 15:10:40. Prof. Doug Hamilton wrote:

Prof. Hamilton,

I have been noticing these 3 stars which sort of lie in almost a straight line. They seem to be pretty bright and the line that they form seems to be pretty prominent and obvious. I started noticing them around the time the meteor shower occured. It would be very interesting to know what they are, and if they are sort of part of the same system. If you understand which stars I am referring to then please do reply.

Thanks a whole lot!! -Ambreen.

Hey Ambreen,

I bet that you are seeing Orion's belt. Take a look at the inside cover of your ASTR100 book at the picture "The Night Sky in Spring". Look near the Western Horizon. Orion's belt is composed of the three stars near the "N" in the word "ORION". The stars are not members of the same star system, but are just a chance alignment in the sky. Orion is a particularly interesting constellation - the bright star Betelgeuse is a red giant (and appears noticeably red) and the bright blue star Rigel is a high mass main sequence star. See if you can spot Orion in the sky!

Doug Hamilton

MESSAGE #148. Wed Nov 24 7:55:55. Prof. Doug Hamilton wrote:

All excellent points Eric! Looks like everything one needs to know about radio waves can be found here on the ASTR100 Bulletin Board.

A quick reminder ... the LAST day for attending the open house is Sunday December 5! Don't forget to do this important part of ASTR100.

MESSAGE #147. Tue Nov 23 15:01:05. Eric Webster wrote:

Re AM vs FM --

It really depends on how you define "messed with". Trees and buildings make decent FM barriers, but lousy AM barriers. And AM waves will 'bounce' off buildings, cliffsides, and even the atmosphere while FM waves get scattered by them. The AM bounce-off-the-atmosphere is recognizable to anyone who has driven across the country; near Mt. Shasta, my International TravelAll's AM radio got its best nighttime signal from KFI in LA some 700 miles away!

Now I know TV uses VHF and UHF, but the ad $$ are much smaller for UHF channels. Does the higher frequency of the UHF signal allow it to get more easily disturbed than the VHF signal?

What bandwith are the radio waves we 'see' from stellar nebulae? It must be a whole range, right? Those radio telescopes probably get good AM radio reception!

MESSAGE #146. Tue Nov 23 14:46:29. Prof. Doug Hamilton wrote:

The differences between AM and FM reception are interesting but it is actually the AM waves that are more easily messed with! This is because scattering (which is greater for shorter wavelengths) is not the main problem for radio waves, diffraction (greater for longer wavelengths) is.

Driving through a tunnel you can get an FM station but not an AM one (I just tried this again the other day on 395 North under the mall in downtown DC). This is because the (shorter) FM waves can follow you into the tunnel while the AM waves (longer) cannot. To fit through an aperture, the wavelength of EM radiation must be much smaller than the size of the aperture. AM radio waves have wavelengths of a few hundred meters while FM radio waves have wavelengths of a few meters (see below). The tunnel might be 10 meters wide. So FM can get in and AM can't.

The dish for a radio telescopes can be built from wire mesh for the same reason - radio waves won't get through the holes. The same happens for visible light. Light can get through a normal-sized hole in a sheet of paper, but not through a very tiny hole. How tiny? About the size of the wavelength of visible light. Any hole smaller that about a micron or 1/50 the width of a human hair will not let visible light through.

You can also work out the wavelength that a radio station transmits at yourself from the station's frequency. It turns out that

(frequency)*(wavelength) = (speed of light)

for all EM radiation. So

(wavelength)=(speed of light)/(frequency)

Maybe your favorite FM station has a frequency of 101.1 MHz (Megahertz or million Hertz where Hertz has units of 1/s). The station transmits at a wavelength of

(wavelength) = (3*10^8 m/s)/(101.1*10^6 Hz) = 2.97 m

While an AM station that you never listen to transmits at 1000 kHz transmits at a wavelength of

(wavelength) = (3*10^8 m/s)/(1000*10^3 Hz) = 300 m

So, why do you never listen to that AM station? It because no one else does either! A station with relatively few listeners gets little advertising money and can't buy into the "expensive" FM part of the EM spectrum! Why is FM expensive? Because it transmits with less interference (see above) so everyone wants their station to transmit there. If an AM station got popular, it would make more money, and eventually buy its way into the FM frequency. I know of one case where that actually happened! Notice also that the "coolest" FM stations are usually in the 100 MHz range rather than the 90MHz range as well.

So, if advertising $$ are all important, at what frequency do you suppose TV station transmit?

MESSAGE #145. Tue Nov 23 7:16:47. Eric Webster wrote:

That's right Katrina! Christina, maybe it helps to remember that the shorter the wavelength, the more easily it is messed with. That's why FM radio signals get blocked more easily than AM signals--shorter wavelength.

So in the VISIBLE part of the spectrum, blue (shorter) gets scattered all over the 'dome' of the sky more easily than the red, which makes more of a direct path from Sun to eye.

Does this help?

MESSAGE #144. Mon Nov 22 23:00:13. Katrina Martinez wrote:

Christina--my notes say that the sky is blue because the atmosphere scatters short wavelength light better than long wavelength light. Blue light is scattered better than red because blue light has shorter wavelengths. An observer sees wavelengths that are scattered most efficiently, wavelengths that correspond to blue light. I think that's why the sky is blue.

MESSAGE #143. Mon Nov 22 20:35:35. Christina Roney wrote:

Ok, on the short answer to the exam; the one about sorting the electromagnetic radiation waves from shortest to longest is confusing me.

The correct answer is (shortest to longest): gamma rays, x-rays, ultraviolet, blue, yellow, red, infrared, and radio.

This however, does not make sense to me because I thought the sky was blue because of the longer wavelength getting "stuck" in our atmosphere so that's the color we see bending towards our eyes. So how can blue light have a shorter wavelength and red have a longer one if we see blue as the color of the sky and not red?

MESSAGE #142. Mon Nov 22 15:05:22. Eric Webster wrote:

Never mad at you Katrina! But the curve DOES (almost imperceptibly, one might say) change as a result of the correction. If EVERYONE put the right answer and it was marked wrong, then you would be right and it wouldn't matter. However, before this was brought up, the people who put the wrong answer down were scoring higher than they should have been AND there were lower scores for those of us who DID have the right answer. So the mistake caused TWO errors in the curve, one of which has been corrected. In Dr H's munificence, the lucky mistake-makers will not lose points (though I really doubt that those people would get all the rest of the q's correct).

It's kind of off-topic, I suppose, but it IS the grading for ASTR100 so there's a justification. And two points out of 750 still isn't likely to make or break anyone's grade..

MESSAGE #141. Mon Nov 22 11:37:33. Katrina Martinez wrote:

Eric--Didn't mean to imply that all you cared about was the two points on that multiple choice question. I just commented on that because I studied the bell curve a little bit in elementary calculus, and I thought that the curve would change by a translation or something like that. We all know that you're one of the rare students who's in college to (God forbid) learn something. Hope you're not mad at me; it's no fun sitting in the front row if there's no one to make fun of Dr. Hamilton with.

Anyway, Kristina asked about posting something on the bulletin board: I think the very first message posted was by Dr. Hamilton, who said that you'll earn 4 bonus (extra credit) points for posting something. But I don't think it's incorporated yet into the grades that are posted on the web. Makes sense, because you'd want to wait until the end of the semester to record all the points.

MESSAGE #140. Mon Nov 22 10:48:18. Kristina Mechelis wrote:

I have been watching the sky for the past few days and last night it was so beautiful. The moon was full and I pointed out Jupiter and Saturn to a friend of mine and he thought I was really smart. I have a question about this bulletin. Do you get points for posting something and if so how many points and are they just added as extra credit points? Thanks.

MESSAGE #139. Mon Nov 22 8:18:11. Prof. Doug Hamilton wrote:

Hi Class,

Well, we messed up again ... that multiple choice question was graded incorrectly on almost everyone's test. I graded most of the makeup exams by hand (correctly!) later, which is when I first noticed the problem. So Linking telescopes together is the correct answer!

If you marked the correct answer and got it wrong, show your exam to your TA in section and we'll add two points to your score. If you marked the wrong answer and got it right, you win - you get to keep the points!

Sorry about the confusion.

MESSAGE #138. Sun Nov 21 21:10:01. Eric Webster wrote:

Katrina -- I really just want to understand astronomy to the best of my ability (within the confines of a 100 level course), and know when and why I get something wrong. It's the rare student where two points one way or the other (out ASTR100's 750) changes their grade. Pretty bright disk of green cheese (that IS what the Moon is made of right?) tonight. Full tomorrow?

MESSAGE #137. Sun Nov 21 14:23:20. Katrina Martinez wrote:

Thanks, Eric, for your insight on watching Jupiter and Saturn in the night sky.

I also put as my answer to the telescope question, "linking a series of telescopes together." From the way they're presented in the book, resolution and resolving power appear to be the same. Since resolving power depends on diameter, linking telescopes together would increase resolution by making a bigger diameter. Didn't Dr. Hamilton put up a transparency in class that showed many telescopes linked together?

Anyway, I don't think the two points on that multiple choice question really matters. If we got that question right, most of the grades in the entire class would be shifted 2 up, and so the curve would actually stay the same.

MESSAGE #136. Sat Nov 20 21:02:14. Monique Koppel wrote:

Eric I also wrote as an answer to the radio telescope question - linking a series of telescopes together. I think that it was an example given in class of how to increase resolving power. If you find out the correct answer and the explanation to that answer let us know.

MESSAGE #135. Sat Nov 20 14:17:04. Eric Webster wrote:

Katrina -- I believe you're right about the bright objects near the moon being Jupiter and Saturn. Jupiter is easily the brightest thing in the sky at night (except the moon). Saturn is more starlike in intensity (flux), but if you draw a line from the moon to Juipter and continue to the left, Saturn is right there.

Now: There was a question on the test about increasing the resolution of a radio telescope. By resolution, I interpreted resolving power. Therefore, I put as an answer that they would link a series of telescopes together. However, the correct answer was something like measuring one side of the object and then the other. I REALLY don't understand this approach. Perhaps a TA or the test-writer can clarify this for us..

MESSAGE #134. Fri Nov 19 18:58:31. Katrina Martinez wrote:

The moon looks really pretty in the sky from LaPlata. I've been watching it for past couple of days; it's really hard to miss since it's the only thing in the sky. Anyway, the moon is 3/4 full (or 1/4 empty, depending on your outlook on life), and the phase is waxing gibbous? I saw two stars, one that looked brighter and slightly larger than the other, that I assumed to be Jupiter and Saturn.

MESSAGE #133. Wed Nov 17 23:55:02. Katrina Martinez wrote:

I just came from LaPlata Beach, where I sat for a while looking at the sky. Unfortunately, I couldn't stay very long, but I did see points of light that were either comet debris or light doing funny things to my glasses. It's difficult to find a dark enough place in North Campus because the area is fairly well lit. Lots of light is good for safety, but bad for astronomy; that's why there's so much controversy surrounding the dark sky ordinances.

The next best way of viewing the Leonids is by looking at today's Astronomy Picture of the Day. This one is good because it's a moving image of the 1998 meteor shower that was seen in New Mexico. However, a better picture is an archived stationary image of the 1998 Leonids because the frame freezes right when the meteor takes on a form. Some people said that it looks like an angel; I thought it looked more like the mythological Phoenix bird that destroys itself every 500 years, but always rises from its ashes. I like my interpretation better because it's much more creative.

MESSAGE #132. Wed Nov 17 10:40:44. Prof. Doug Hamilton wrote:

Why is the corona hot?

Remember the corona is about 1,000,000 degrees while the Sun's visible surface is only 6000 degrees. This is unusual - since the corona is further from the center of the Sun we might expect it to be cooler than the visible surface.

The first step toward answering this question is to figure out what energy sources are available for heating the corona. The main possibilities with enough energy include 1) the photons streaming off the Sun's visible surface and 2) magnetic fields which are known to determine some of the corona's structure. The first energy source has problems. The corona is so hot that atoms do not exist there - just atomic nuclei and electrons. These are not very efficient at absorbing light, so not enough sunlight is absorbed to heat the corona up much.

So we are left with magnetic fields. Most everyone agrees that magnetic fields are responsible, but the details of exactly how this works are not understood. There are two or three rather technical theories, one of which might be right, but there is not enough evidence yet to say which is right (if any are right!).

The book talks about magnetic waves being responsible, but there are a whole zoo of different types of magnetic waves - we don't know which ones are the important ones. People have also argued that magnetic reconnection (which is a different magnetic effect) might be more important than waves. The question is of exactly how the corona is heated is not really settled yet and thus it is an area of active research in solar physics!

MESSAGE #131. Tue Nov 16 11:26:39. Katrina Martinez wrote:

I just came from McKeldin lawn, where the sunpspots are being shown. It's really interesting if you can stand being out in the cold. You can look at the sunspots through a telescope, but you can also see them projected on a small square board. The sunspots reminded me of cell cultures you grow in biology: the sun was the culture, and the sunspots looked like spiral bacteria growing on the petri dish. (I think one of these days psychologists should use pictures of sunspots as one of their Rorschach tests.)

MESSAGE #130. Mon Nov 15 20:20:49. Eric Webster wrote:

Oops I meant Post #118 re: superhot coronae..

MESSAGE #129. Mon Nov 15 20:19:26. Eric Webster wrote:

Ambreen --

It was raining last Thursday, so they are scheduling the sunspot viewing for tomorrow. It's supposed to be pretty cloudy tomorrow, so we'll see if they show..

Dr. H or George -- Can you shed any light [sic] on the second part of post 119 on the hot corona conundrum? TIA..

MESSAGE #128. Mon Nov 15 17:46:54. Ambreen Ilyas wrote:

Hi everyone, Just wanted to ask if the sunspot viewing ever took place last Thursday? I hope not cause it was raining and so i did'nt actually go to check it out. But if it did'nt take place on the 11th is it taking place tomorrow i.e. 16th Nov? Thanks!

MESSAGE #127. Mon Nov 15 16:45:15. Prof. Doug Hamilton wrote:

Hey amateur astronomers, this might be good! Check out the Leonid Meteor stream late Wednesday night and early Thursday morning. http://www.skypub.com/sights/meteors/leonids/9911planwatch.html

The Leonids come from Comet Tempel-Tuttle which has a 33 year orbit around the Sun. Since the comet has just passed Earth, and the region just behind the comet has lots of debris, this should be a particularly good year for a meteor storm. In a typical year the Leonids cause something like 10 meteors per hour - a "storm" this year could result in 1000 meteors per hour! Pretty impressive if it happens, but these things are hard to predict.

Last year was also pretty good - even though it was cloudy then, I saw 10-20 very bright shooting stars from College Park. If you can get to a darker site, you will be likely to see lots more this year.

MESSAGE #126. Sun Nov 14 23:44:57. Benjamin Rodeffer wrote:

Thank you Mr. Webster for your information. I'm considering it as a winter break project.

MESSAGE #125. Sun Nov 14 17:05:11. Eric Webster wrote:

Benjamin --

I believe you are referring to a Dobsonian telescope. Pretty easy and inexpensive to build, but you still need to purchase the focusing mirror, reflecting mirror and the eyepiece. All told, it sounds like a coupla hundred for the optics and about fifty for the rest.

A list of Dobson DIY (do it yourself) sites are at:

http://dir.yahoo.com/science/astronomy/telescopes/amateur/telescope_making/dobsonian_telescope/

From the links there you can get to the optics suppliers for pricing info.

If you make one, let the board know and you'll be a hero!

MESSAGE #124. Sun Nov 14 16:42:49. Benjamin Rodeffer wrote:

Don't ask me why but, I was watching the movie "Can't Buy me Love" Friday night. In the movie he had a cardboard tube that was a telescope. I was curious if there was such a thing. If so, does anyone know how to construct such a thing?

MESSAGE #123. Thu Nov 11 11:32:22. Christina Roney wrote:

Hello everyone! I was just looking on my internet's home page and they had an article about 4 astronauts that are set to go "fix the Hubble". I didn't know that the Hubble needed fixing again since we last put lenses on it to correct the error with the mis-ground mirror. Also a couple days ago there was an article about how the Hubble was witnessing a collison of 2 star systems (galaxies?). I thought this may have been interesting to some of you. Ok, c ya later! Good Luck on the Exam tomorrow every one!

MESSAGE #122. Wed Nov 10 19:01:44. Prof. Doug Hamilton wrote:

Thanks for clearing that up Katrina - your guesses are right on!

Focus George, Focus! Those are interesting questions, but not exam II material! We'll get to black holes soon, though! They do absorb all light that falls upon them (which is why they are black), but there are not enough of them to cause space to be cold. Space is cold simply because there is so much of it between the hot things (stars). If we didn't have the Sun, for example, starlight wouldn't be able to heat things up too much. Trying to heat up space with starlight is a little like trying to warm up a dank old castle with a single candle.

MESSAGE #121. Wed Nov 10 18:53:22. Prof. Doug Hamilton wrote:

Prof. Hamilton,

I dont quite understand why the sunsets and sunrises are red. I dont particularly understand how come the light has to go through more atmosphere when the sun is at the horizon. Also since short wavelengths are scattered what happens to the other wavelengths of light. How come we dont see other wavelengths? Does it mean that there is dispersion going on due to refraction of light as it passes through the atmosphere? Where does the wavelengths combine? I guess I am confusing this with dispersion. But I really dont undestand what exactly you mean by scattering of blue light?

I would appreciate it if you could explain this to me.

Thanks in advance. -Ambreen

Hi Ambreen,

Those are good questions! Sorry for the delayed response ...

Try drawing a picture! Too bad I can't do this in HTML. Draw a circular Earth so that it takes up most of a sheet of paper. Then draw a thin atmosphere around the Earth (a slightly bigger circle). Now draw a tiny little portrait of yourself at the 12 o'clock position on the Earth's surface. Finally, draw a vertical line from your portrait straight up (that's the light ray to the noontime Sun) and another one out horizonally out to the 9 o'clock position (that's sunset). If you drew the picture well, it should be clear that the horizontal line cuts through more atmosphere than the vertical line does. For the actual size of the Earth and the thickness of the atmosphere, the sunset ray travels through something like 20 times more atmosphere than the noontime ray.

All wavelengths of light are scattered in the Earth's atmosphere. Yellow, for example is scattered more than red but less than blue. When we look toward the Sun, we see the light that is not scattered (it comes straight to us). So sunsets are a mixture of lots of red, a little yellow, and even less blue since the yellow and blue are mostly scattered to other directions. This combination looks red to our eyes. Conversely, when we look away from the Sun, we see the scattered light which is mostly blue, a little yellow, and even less red. This combination looks blue to our eyes.

Whew! Does that all make any sense??

MESSAGE #120. Wed Nov 10 18:16:38. George Morgan wrote:

Professor Hamilton, I understand all that you taught about darker colors reflecting less light than brighter colors, but I have a q. Does this mean that the Black Hole(s) in space absorb all excess heat/energy/light and is filled with it, or disperses it through space or so? Is this why space is kept so cold or not?

_George

MESSAGE #119. Wed Nov 10 14:36:57. Katrina Martinez wrote:

Someone today asked if Overview 4 was going to be on the exam. According to the lecture schedule, Overview 4 is going to be on Exam II, along with Overview 5, Essay 2, and chapters 3, 5, 9-11. Although Overview 4 was not assigned in the reading for Exam II, it does contain some information on the Oort Cloud and the Kuiper Belt. Overview 5, which comes right before Chapter 11, discusses hydrostatic equilibrium and the proton-proton chain, stuff in Chapter 11. Incidentally, it also talks about the end of a star's life.

Essay 2 seems irrelevant to what we're studying right now because it's on keeping time.

In short, out of Essay Two, Overview 4, and Overview 5, my guess is the only things that may appear on Exam II is Overview 4 pp. 214-215, and Overview 5 pp. 319 to 321.

MESSAGE #118. Wed Nov 10 13:56:00. Eric Webster wrote:

Boy those big stars are hydrogen hogs, aren't they?

I feel pretty sure this WON'T be asked on the exam, but I need a better explanation on why the corona gets so hot.

The book mentions that the density further away from the surface of the Sun is much less, and the gravitational fields of the Sun (which are not decreasing) excite the farther atoms to a much greater extent than the closer-in atoms, heating them intensely in the process.

eg force of e/m energy constant, but fewer number of atoms to excite = very excited remaining atoms

In fact, the book goes so far as to state that it excites the atoms so much as to cause the 'solar wind'. Is this a fair assessment of the phenomenon?

MESSAGE #117. Tue Nov 9 19:26:56. Prof. Doug Hamilton wrote:

How long do you think stars with hot interiors will live in comparision to our Sun? Hot temperatures mean that the Hydrogen ions will move very very fast - this will change the rate at which stars use up their Hydrogen fuel.

We'll get to this stuff next week (after the exam!).

MESSAGE #116. Tue Nov 9 19:13:00. Monique Koppel wrote:

Eric, You asked about temp of hotter and bigger stars? Well,I found that stars of high mass were carbon fusion takes place (in their core), have a temp that exceeds 600 million K in the core. As for a formula? I don't know.

MESSAGE #115. Mon Nov 8 17:42:26. Eric Webster wrote:

So we know the Sun's internal temperature = 1.5 * 10⁷° Kelvin.

We also know stars come in much hotter varieties than Sol.

How much hotter are the interiors of the really hot stars? Charles took a guess at it in section, but the speed of his backpedaling (and his subsequent confession) indicated he wasn't too sure. Is there a formula for deducing the interior temperature of a star from its exterior temperature?

MESSAGE #114. Sun Nov 7 17:09:07. Courtney Perkins wrote:

Thanks Eric, I really do appreciate your help.

MESSAGE #113. Sun Nov 7 17:08:02. Courtney Perkins wrote:

Thanks Eric, I really do appreciate your help.

MESSAGE #112. Sat Nov 6 9:16:05. Eric Webster wrote:

Courtney --

I wasn't there for Ji-Hoon's comet-tail lecture, so I can offer my own understanding of the phenomenona. Two discrete tails form from comets, one a gas plume; one composed of dust and teeny tiny pieces of rock. The gas is lighter, so the solar wind can "blow" it more effectively and consistently in the direction AWAY from the Sun. The dust tail has heavier "pieces", so it kind of drags behind the gas tail. If you remember that the dust plume is heavier than the gas plume and you can draw a picture of a comet's motion around the Sun, it's easier to understand. Fig. 10.15 on page 309 in the book is just that sort of diagram!

Exam alert! The inside scoop is that there are going to be lots of questions about asteroids, comets, and the physics of light (aka electromagnetic radiation) on the exam. The good news is that there are only 10 lectures worth of material to review!

MESSAGE #111. Fri Nov 5 16:53:56. Courtney Perkins wrote:

I was wondering if someone, particularly someone that is in discussion section 0206, could explain to me what Mr. Kim was saying about the dust tails and the other comet tails. He said that he explained/drew the dust tails incorrectly last time and that they should be facing the other way due to solar wind, is this correct? I am unsure about his exact reasoning. If someone could clear this up for me I would appreciate it. Thanks!

MESSAGE #110. Fri Nov 5 16:44:49. Eric Webster wrote:

Hey how'd you know I was here?

Sorry I can't help on the sunspot question -- you didn't miss anything! We know the sunspots are cooler, but we haven't yet heard from Prof Hamilton why they are cooler. If not knowing about the 'spots keeps you awake tonight, the book offers its own reasons: it never fails to put me to sleep!

MESSAGE #109. Fri Nov 5 11:43:15. Ambreen Ilyas wrote:

Eric could you please explain why the sunspots are cooler than the rest of the surface? I guess I did'nt quite catch that in class today. Thanks!

MESSAGE #108. Thu Oct 28 16:08:32. Ambreen Ilyas wrote:

Hello everyone and thanks for answering my question. I guess the fact that moon rises around 7:30 pm these days explains why it was so low in the sky since I saw it at about 8:00pm or so. I guess I never noticed the moon that much before, and since I have been in the US and Maryland for only about 10 months and before that I lived close to the equator and so I never noted the moon to be so low in the sky in my country(or maybe I did, i dont remember).

MESSAGE #107. Thu Oct 28 7:00:18. Eric Webster wrote:

I focused the lens' on my cheapo 10x binoculars, and I could make out the ring (and its shadow!) of Saturn much more clearly.The image still jumps around a lot, so it looks like I will have to invest in a tripod for more stable viewing.

BTW, I discovered numerous websites for plans for homemade telescopes. The optical stuff (mirror, eyepiece) cost real money (150 or so), but the other material (tube, base, etc) is inexpensive. It's probably cheaper and more fun to go to the OPen Houses at Campus...

MESSAGE #106. Wed Oct 27 21:03:25. Monique Koppel wrote:

Ambreen, I think you have to clarify what do you meen by low. First, it depends on what time of the day or night you saw the moon. At this stage of the moon (waning gibbous) the moon rises around 7:30 or maybe a little later, and it sets around 8 am or so. Hence, the moon shoul be at its highest point in the sky sometimes after midnight. However, since we are in MD and not on the equator, we never see the moon at exactly 90 degrees but at a lower angle. I hope this helps.

MESSAGE #105. Wed Oct 27 19:32:36. Eric Webster wrote:

Ambreen --

If I may, let me try giving your question a shot. And please, if I'm totally wrong, correct me!

All the planets (Sun, Moon, Saturn, Mars, etc) rise and set ech day, rising in the East and setting in the West.

All this rising and setting activity is due to Earth's rotation. We spin and our view changes like your view on a carousel changes while it's moving.

From day to day, Earth's position changes due to our orbit of the Sun. The other planets' positions change too due to THEIR orbits of the Sun. So from day to day, the planets' positions in the sky change because 1) they are moving around the Sun (Merc and Venus more quickly than Earth, outer planets progressively less quickly than Earth) and 2) our position relative to theirs is changing as well.

Imagine being on a carousel, looking out at the crowd. Then you notice a couple of kids running around the carousel at different speeds. Sometimes you see one kid, sometimes you see both, sometimes you don't see either (when the carousel is in the way). Does that metaphor hold water? (just practicing a little metaphor-mixing )

Does this help at all?

MESSAGE #104. Wed Oct 27 14:07:29. Saadia-Yael Eisenberg wrote:

The moon this morning seemed, by 730 am, to be very light blue. Is this the optical illusion due to a prism-spectrum of light or because its becoming colder-seasonal change? The mares seemed also kind of tan-grey.

MESSAGE #103. Wed Oct 27 14:04:21. Peter Miller wrote:

I've noticed in the last couple of days that a near-full Moon is visible at about 20-25 degrees above the horizon, when I drive to school in the morning.

MESSAGE #102. Wed Oct 27 13:51:26. Ambreen Ilyas wrote:

Prof Hamilton, I noticed the "stars" near the moon on Sunday nite but I had no idea what they were. When i read your message the other day it flet really cool to know that they were Jupiter & Saturn.So last nite i showed the 2 planets near the moon to my husband. He was pretty impressed. I have a question though, why did the moon seem to be so low in the sky?

MESSAGE #101. Wed Oct 27 11:04:40. Prof. Doug Hamilton wrote:

The grades keep taking longer than I expect, but I will definitely have the exam grades posted this afternoon or early evening (finally). Exams will be passed back in section starting Friday. This really has been too long to wait for all of you - I promise that the TAs and I will be more prompt with the grading of the next exam.

The Open House Papers are mostly graded, and will be posted by Monday at the very latest. Those of you who have not done the Open House Paper yet will have artificially low grades on the grade page since you'll have a zero for the assignment until you turn it in! Don't be too alarmed by this!

Finally HOMEWORK #5 is due on Friday! These will be graded and posted by Monday or Tuesday.

MESSAGE #100. Tue Oct 26 23:24:21. James Blassingame wrote:

Professor Hamilton, I have a quick question. When will the Open House and first exam scores show up on the What's My Grade?

MESSAGE #99. Tue Oct 26 22:07:33. Jillian Martin wrote:

Last night while I was in Orlando Florida there was an full harvest moon in the sky. It was so pretty, people must have thought I was nuts because I stood there and stared at it for the longest time.

MESSAGE #98. Mon Oct 25 18:43:15. Prof. Doug Hamilton wrote:

The planets near the Moon last night (and tonight) are Jupiter (very bright) and Saturn (fainter). Take a look tonight - it should be impressive!

MESSAGE #97. Mon Oct 25 18:34:20. Christina Roney wrote:

At about 9:30 last night I was gazing at the moon. It was very brilliant when not hiding behind the clouds. I also noticed two planets pretty close in proximity to the full moon. One was at about 1:00 and the less bright one at about 8:00. I'm not sure which ones they were, but it would be nice to know. Happy almost Halloween everyone!!

MESSAGE #96. Mon Oct 25 14:22:31. Saadia-Yael Eisenberg wrote:

Yesterday I flew into Washington, DC around 10pm and as I was wheeled around on the concourse (I flew in a smalllll airplane)the whole tarmac was seemingly illuminated by a most brilliant large full moon, there were two "stars" very close to it that were quite bright...what were they? One was at roughly 2:00 and the other at about 1930. Were they planets? Who can explain why they appeared so close to the moon at 10 pm (Wash. time?)The stewardess was impressed and I had the young pilot stargazing for a whole ten minutes while we discussed the moon, pretty cool eh?

MESSAGE #95. Mon Oct 25 14:20:29. Saadia-Yael Eisenberg wrote:

Yesterday I flew into Washington, DC around 10pm and as I was wheeled around on the concourse (I flew in a smalllll airplane)the whole tarmac was seemingly illuminated by a most brilliant large full moon, there were two "stars" very close to it that were quite bright...what were they? One was at roughly 2:00 and the other at about 1930. Were they planets? Who can explain why they appeared so close to the moon at 10 pm (Wash. time?)The stewardess was impressed and I had the young pilot stargazing for a whole ten minutes while we discussed the moon, pretty cool eh?

MESSAGE #94. Mon Oct 25 1:10:34. Shelley Dezelon wrote:

Hey, I went to the Air and Space mueseum at DC and saw "Star to Steer her by" at the Planetarium...it was very interesting, about how sailors navigate by the stars.. It also helps to understand the movement of the stars throughout the year...so if you end up going there sometime, I'd advise you to go see it!

MESSAGE #93. Sun Oct 24 9:31:19. Eric Webster wrote:

Well, I can't tell anyone what they saw, but I can guess at what I saw (mind you, I was using hand-me-down Sears 10x binoculars!):

To the left of the full moon was Jupiter, super-bright with two visible moons on its right.

Further to the left of the Moon and Jupiter, there was a brightish-star-like body that I guessed was Saturn. I tried to hold the binocs as steady as possible, contorting my viewing position so I could hold them close to the side of the house. (So I'm too cheap to spring for a tripod!) Anwyay, I THINK I saw the rings of Saturn. The jiggling around made it pretty tough. Maybe I'll start pricing tripods. Or telescopes..

Does anyone know where one can find plans online for make-em-yourself telescopes? I heard there was a fellow in SF who is sort of a Johnny Appleseed of DIY large scale scopes.

MESSAGE #92. Sat Oct 23 20:25:21. Quan Luu wrote:

10/23/1999 - I was out with my boyfriend and I saw a full moon and a very bright object near it. Can anyone tell me what it was? A planet? A star?

Quan

MESSAGE #91. Wed Oct 20 16:55:32. George Morgan wrote:

NASA said hubble caught images of a dying star. More information can be found at http://www.msnbc.com/news/325105.asp

As far as it goes, they will use this new-found information to determine more information about the longevity of our Sun.

MESSAGE #90. Wed Oct 20 13:38:26. Saadia-Yael Eisenberg wrote:

The other day there was an interesting article in the newspaper about the Hubble -was it discovering new realms in a galaxy? I will reread and post the jist of it, seemed very in line with our coursework-upcoming doverage of galaxies etc.

MESSAGE #89. Sun Oct 17 22:31:28. April Jackson wrote:

Good Luck to everyone on the exam tomorrow!!!

MESSAGE #88. Sun Oct 17 19:23:24. Benjamin Rohan wrote:

lets get some beer and go look at the moon

MESSAGE #87. Fri Oct 15 21:09:02. Eric Webster wrote:

Thanks April. And thanks to the rest of the BBS community (and ASTR 100, for that matter) for putting up with me! I found Charles' review useful -- I hope the exam isn't too tough!

MESSAGE #86. Fri Oct 15 19:19:53. April Jackson wrote:

Yes Eric I will accept your apology. The reason why I was so persistent in saying that it was Venus is because my boyfriend was with me that night and this is his major, he knows all about space and that sorta thing. So when we saw it, I wanted to know which planet it was so I could write it on the message board. He told me it was Venus and I believed him because this is his major. I also thought it was Venus because Venus is closer than Jupiter, and this "star" was very very bright.

MESSAGE #85. Fri Oct 15 7:33:28. Eric Webster wrote:

I apologize to April and all the members of the board for sounding so smug about whether it was Venus that April saw recently. It is certainly very smart and resourceful of April to be watching the sky at night while taking an astronomy course!

I am NOT trying to sound like a know-it-all but I AM trying to figure this astronomy stuff out. If someone posts an observation that doesn't jibe with what I've read, I want to understand where the difference lies.

I do remember from the book that Venus and Mercury are always observed in the general direction of the Sun from Earth's direction--their orbits are closer to the Sun, so from Earth, they can be a maximum of maybe 27? degrees from the Sun (Mercury) and 40? degrees from the Sun (Venus). So my theory (and you are right April, it is just a theory--I wasn't there observing with you) is that at 10pm the sun is long set, and Venus would either be very low in the western sky or not visible.

Anyway, will you accept my apology April ?

MESSAGE #84. Fri Oct 15 4:16:17. Prof. Doug Hamilton wrote:

Venus and Jupiter are both very bright planets. Currently Venus is visible in the morning low near the direction of sunrise. Jupiter is high the sky and pretty close to Saturn (which is bright, but not as amazingly bright as Jupiter and Venus). Everyone should follow April and Eric's lead and try to identify a few planets. Amaze your friends with your practical astronomy knowledge!

Actually, the person who finds the fainter planet should get the cookie! Fainter planets are much harder to find. Can anyone find Saturn from my description and the fact that it must lie along the ecliptic (the path taken by the Sun, Moon and planets across the sky)? The secret is "connect the dots". Connect up the Moon to Jupiter and extend the line to the two horizons. Then look for other bright objects along the line (which is just the ecliptic).

Saw the Moon from Italy - it's a thin waxing crescent. Waxing means getting more full! It is visible in the evening and will be rising higher and higher in the sky in the coming days.

MESSAGE #83. Fri Oct 15 0:11:03. April Jackson wrote:

So what do you want a cookie? We are in college and there is no need for games. What is with the line "I bet it was brighter than the 10:00pm star". Congratulations if it was, I was not trying to play "I bet the star I find is better than yours" game. That is just being childish. The whole point of the bulletin board is to inform others of what you observe and that is what I observed. Oh yeah, I really don't remember seeing YOU while I was observing VENUS so you really can't tell me what I saw.

MESSAGE #82. Thu Oct 14 15:59:11. Akisha Jones wrote:

Good luck on the exam Monday everyone! Don't forget review session tonight!

MESSAGE #81. Thu Oct 14 6:54:33. Eric Webster wrote:

Very bright object in the sky at 6:45 this am. I bet it was brighter than the planet sighted at 10:00pm last Friday! It might have been the sleep in my eyes, but I'd guess it was the brightest object in the night sky! Looked big too! I wonder if Venus is "full"...

MESSAGE #80. Wed Oct 13 13:08:03. Saadia-Yael Eisenberg wrote:

This monday was Rosh Chodesh Cheshvan..the new month by our lunar calander. When I went on tues. nite to the excellent Planetary Nebulae lecture of Dr. JP Harrington I could hardly see my own legs as I walked about. yet when looking through the 20" Eichner Bent Cassegrain Reflector telescope at the Ring Nebula you could only just make out the grey hazy gaseos "shell" surrounding the black center. The surface lights of the nearby villages and larger cities kept the telescopic visibility low, but the slide show and lecture were simply marvelous.I was wondering what our rotc-Air Force students thought about the presentation and if they could share with us what its like in the nite sky at 48,000'- going MACH 1-2?

MESSAGE #79. Wed Oct 13 7:14:55. Eric Webster wrote:

Did anyone else see the Time mini-article on our own Solar System's asteroid Eugenia that has captured a satellite of its own?

Not a very dense asteroid either. Using the effect of gravity on the captured moon, they have inferred that Eugenia has a density of only 2.5 gm/cm³

I guess this gravity biz isn't limited to giant spheroids!

MESSAGE #78. Mon Oct 11 4:30:10. Prof. Doug Hamilton wrote:

New Result from the Planetary Science Meeting:

4 New Moons of Uranus have been discovered! The first one was found in images from Voyager from 1986 - it was overlooked all of these years. It is located close to Uranus, and probably formed when the planet did.

The other three were discovered with ground-based telescopes. They move on distant orbits and are probably captured objects.

MESSAGE #77. Sun Oct 10 21:14:34. Eric Webster wrote:

re: Message 76 Hmm. Venus at 10:00pm.. How do you know it wasn't Jupiter or Saturn?

MESSAGE #76. Sun Oct 10 18:43:32. April Jackson wrote:

Hi everyone I just thought you should know that I saw Venus in the sky on Friday night around 10:00 p.m.

MESSAGE #75. Sun Oct 10 16:02:17. James Blassingame wrote:

Hello, Everybody. Good luck on the test next Monday.

MESSAGE #74. Sat Oct 9 13:29:59. Prof. Doug Hamilton wrote:

Have a good week everyone! Study hard for the first exam and start early so you won't be overwhelmed by all of the material! I'll see you on Monday morning October 18th.

Don't forget to watch the Moon while I'm gone!

MESSAGE #73. Fri Oct 8 10:20:49. Prof. Doug Hamilton wrote:

I forgot to announce this this morning in class:

Juhi found a pair of glasses after one of her Wednesday sections in CSS2400. They are in a hard case which is black on the front and silver on the back. The front side has a picture of an eagle and the words "Harley-Davidson Motorcycles".

If these are yours, you can pick them up in the Astronomy Mailroom, CSS1204.

MESSAGE #72. Thu Oct 7 20:50:37. Imran Shaikh wrote:

Hello !!!!!!!! every1.....

i have finished my hw #4!!!!! and right now i'm listing to Indian song on line so anywayyyyy if anyone need helpe e-mail me at ishaikh@wam.umd.edu * * * * )* * /\ * * /\ * || || || || || WELCOME || |||||||||||||||||||| || |||||||||||| || |||||||||||||||||||| ||||||||||||||||||||

MESSAGE #71. Thu Oct 7 19:37:48. George Morgan wrote:

Hey, does anyone notice that when you try to skim over questions or any text on the CD-ROM that you can only see fragements and not the entire statements? I'd like to know if anyone else has this prob. Thanks..

GEMII

MESSAGE #70. Wed Oct 6 10:32:58. Prof. Doug Hamilton wrote:

This is a response to Saadia-Yael (Msg. #61).

When an object is low near the horizon (as compared to high in the sky), its light has to go through more of Earth's atmosphere before it gets to us. This effect is why the Moon usually appears reddish on the horizon (and sunrises and sunsets look reddish too). Red light is better able to get through the atmosphere than other colors. And, more relevant to your question, if there are thin clouds or haze, the Moon will look a lot fainter when it is on the horizon.

Once the Moon rises high in the sky, though, its light has to travel through less atmosphere and it will appear brighter - bright enough to be seen in the daytime!

So everyone keep an eye out for the Moon during the day too!

MESSAGE #70. Thu Sep 30 21:57:02. Crystal Koch wrote:

anybody in wednsdays discussion 203 class? are t.a. gave us a problem and i have like noooo idea how to go about solving it. any help would bve appreciated. my email is crystalkoch@hotmail.com. thanks

(This was posted to the wrong place! - D. Hamilton)

MESSAGE #69. Tue Oct 5 23:33:49. Christina Roney wrote:

I was just wondering if the movie Armageddon was accurate in the way it portrays the asteroid. They said it was like a metal instead of rock, and the asteroid had bits of ice on it that would evaporate like comets, leaving a tail behind it. That didn't seem quite right to me after what Prof. Hamilton explained to us in lecture about where the rocky, gasseous, and icy objects are in our solar system. What do all ya'll think?

MESSAGE #68. Tue Oct 5 13:38:53. Prof. Doug Hamilton wrote:

Forgot to remind you all about the open house tonight! See the syllabus for details.

Peter - just because it's simple doesn't necessarily mean its wrong! Try drawing a picture.

MESSAGE #67. Tue Oct 5 13:07:14. Peter Miller wrote:

I have a question regarding a problem assigned by our TA. Does anyone know how to figure out the minimum distance between two planets? I have the distance from the Earth to the Sun and I also have the distance from Jupiter to the Sun. Do I just subtract the two distances? That seems to simple. Any suggestions?

MESSAGE #66. Tue Oct 5 12:56:00. Peter Miller wrote:

No, I was using an IBM in one of the computer labs.

MESSAGE #65. Mon Oct 4 14:56:54. Eric Webster wrote:

Yup. See Message #3. Are you on a Mac by any chance?

MESSAGE #64. Mon Oct 4 10:17:45. Peter Miller wrote:

Has anyone else tried the Even More Computer Programs link? It's supposed to show the orbits of all the moons in our solar system but I get an error message every time I try to use it.

MESSAGE #63. Fri Oct 1 7:06:07. Eric Webster wrote:

PASADENA, Calif. (Reuters) - Human error stemming from space engineers using two sets of measurements -- one utilizing miles and the other kilometers -- caused the loss of the Mars Climate Orbiter spacecraft last week, NASA said Thursday.

The teams, located at the National Aeronautics and Space Administration's Jet Propulsion Laboratory in Pasadena and at Lockheed Martin Astronautics in Colorado, complicated matters further by failing to realize the error, the agency said in a statement.

I guess this is what happens when you don't convert units properly!

MESSAGE #62. Thu Sep 30 20:52:28. Saadia-Yael Eisenberg wrote:

In the morning I could see the moon ever so faintly over the horizon, it was about 6;30am. Why did the moon appear so faint and yet remain noticable for several hours more even while the sun rose?

MESSAGE #61. Thu Sep 30 20:51:01. Saadia-Yael Eisenberg wrote:

In the morning I could see the moon ever so faintly over the horizon, it was about 6;30am. Why did the moon appear so faint and yet remain noticable for several hours more even while the sun rose?

MESSAGE #60. Thu Sep 30 19:30:49. Eric Webster wrote:

The formula for the volume of a sphere is in the book, probably in the chapter that the question id from. They plug that formula into another formula to find density.

Hope that helps!

MESSAGE #59. Thu Sep 30 19:25:07. Heather Grimes wrote:

How do you find the volume of a sphere? Ack, I can't find it in my notes. :( Thanks! --Heather

MESSAGE #58. Thu Sep 30 11:06:08. Eric Webster wrote:

ah converting mesurements: Charles Greenwell's shrewd admonition!

That's where the constant comes in handy. It puts into the equation just the right units that you need, if the equation lacks it.

Otherwise, a meter divided by a meter disappears off the equation.

A meter cubed divided by a meter squared is a meter

and so on

Note that meters of radius or distance when cubed become m³ or cubic meters: a measurement of volume.

Keeping track of the units helps you check for errors in the math. If you get a rate of speed that is in kilograms (for instance), something didn't cancel out correctly!

Does this help?

MESSAGE #57. Thu Sep 30 9:43:53. Kristina Mechelis wrote:

Hi guys, I'm having a little bit of trouble with the math in the homework. I can do scientific notation but I get confused about the other equations. Especially when it comes to converting measurements. Does anyone have any suggestions on how I might understand better? Thanks.

MESSAGE #56. Wed Sep 29 14:10:54. Eric Webster wrote:

So far, all we've been asked to do scientific notation-wise is multiply

10¹² x 10¹⁴

add exponents 10²⁶

Like wise to divide, subtract exponents..

to make an exponent of an exponent ie (10²² ) ³

multiply the exponents: 10 ⁶⁶

Likewise, to take a root power of an exponent, divide the exponent by the root

Beyond this, mathematicians will have to step forward...

MESSAGE #55. Tue Sep 28 21:52:58. Prof. Doug Hamilton wrote:

Michael - sometimes the Moon appears to have a ring or rings around it if there are thin clouds in the sky. The rings come from moonlight reflected off rain drops. If you drink more beer, though, the rings always go away.

MESSAGE #54. Tue Sep 28 20:57:28. Michael Trezza wrote:

Prof. Hamilton, I discovered something quite strange the other night. After drinking beer the moon seems to develop multiple rings around it. I wondered if it has anything to do with atmospheric gasses released from the beer can.

MESSAGE #53. Tue Sep 28 16:11:45. Eric Webster wrote:

Density ... There is a formula for density in that chapter. I believe it is density = mass/volume

Volume of a sphere etc etc.

BTW, you can put that cd in any of the WAM workstations and it will work. The CSS building has great new G3s and there is never a wait!

MESSAGE #52. Tue Sep 28 15:41:01. Saadia-Yael Eisenberg wrote:

Please help with the last homework question. what is the average density of Pluto..I have no idea how to do this problem. How about you Eric, you seem to be on top of the learning processes here. I can't find a computor where I am able to install the software CD Dr. hamilton gave us (came witht he book).

MESSAGE #51. Tue Sep 28 11:50:18. Eric Webster wrote:

Dr. H

I just tried running the solar system viewer on the Macs here at Hornbake and I got the same security code violation error.

I guess I'll have to try one of the Wintel machines next..

MESSAGE #50. Mon Sep 27 19:25:45. Eric Webster wrote:

Lessee.. Houston's on Central time, eh? So it rose there about an hour after it rose here, but our clocks read the same time, mas o meno.. Of course the whole hemisphere (the whole planet if they could see it during daylight) got the same view of the Moon that you and I did..

Did you run into Francis Everitt in Houston?

The class misses you!

MESSAGE #49. Mon Sep 27 19:21:36. Eric Webster wrote:

MESSAGE #48. Mon Sep 27 13:38:45. Prof. Doug Hamilton wrote:

The Moon was a little past full here in Houston Texas last night! It rose around 9:00pm and was just setting at 8:00 this morning. Is this the same as in College Park?

MESSAGE #47. Mon Sep 27 10:40:19. Kristina Mechelis wrote:

I was at a concert Saturday night and the moon looked like it was sitting on the top rim of RFK. And by 11:00 that night it had moved so much. I never really noticed anything about the moon before. It looked so full and bright it was really beautiful.

MESSAGE #46. Fri Sep 24 23:02:18. Eric Webster wrote:

George et al --

I was bummed that my Sears 10x binoculars didn't pick up the rings of Saturn, but I did get to see the Gallilean satellites. Pretty darn cool. If you're not sure about what you're looking at, the cd that came with the book has a decent planetarium software package.

MESSAGE #45. Fri Sep 24 19:39:28. George Morgan wrote:

Yeah Eric, the moon is VERY full tonight. It is very yellowish and bright out. If you look with binoculars, you can see a lot of the craters, at least I believe they are craters and not the clouds..

->George

MESSAGE #44. Fri Sep 24 19:19:58. Eric Webster wrote:

Dr. Hamilton --

If you see Francis Everitt of Stanford (he's been working on Gravity Probe B) at the NASA funding panel. say hello to him for me. He's good friends with my family in Palo Alto.

I had to get the 'noculars out last night to prove to the wife that the Moon wasn't QUITE full last night. Should be pretty round tonight!

See you in a week!

MESSAGE #43. Fri Sep 24 7:47:33. Prof. Doug Hamilton wrote:

Last night around 9:00, the Moon was almost full! It is rising later and later in the evening and is moving across the sky toward a bright star. Actually that bright star is not really a bright star - its Jupiter! Imagine drawing a line between the Moon and Jupiter and extending it all the way across the sky. All the planets (and the Sun and Moon) should appear roughly along that line. Saturn is the bright star (not as bright as Jupiter) visible near Jupiter in the sky.

Watch the sky over the next week to see how close the Moon gets to Jupiter and how close it gets to Saturn. You can measure the distance in Moon diameters.

Mars is also visible high in the sky at sunset. Unfortunately, George's rumor is true - it looks like the latest US Mars mission, Mars Climate Orbiter, burned up in the martian atmosphere early yesterday.

MESSAGE #42. Thu Sep 23 23:47:00. George Morgan wrote:

Hey everyone. I wanted to know if anyone else heard about the Mars Orbiter, if it got fried or not. Last time I heard NASA was not sure. It was launched 9 months ago and they lost contact with it.

-GEMII

MESSAGE #41. Thu Sep 23 16:53:18. Saadia-Yael Eisenberg wrote:

The Jewish sage, the Vilan Gaon established the two hundred year calander based on the lunar cycle. Conmparing his calander to the present day lunar calculations we find that the Gan was accurate to within one half minute of his predictions.

MESSAGE #40. Thu Sep 23 16:42:36. Saadia-Yael Eisenberg wrote:

I just received the national geographic for this montha nd it has a fantastic foldout poster of the Milky Way and there is special section on Nebulae. Anyone see it!!?

MESSAGE #39. Thu Sep 23 14:16:14. Eric Webster wrote:

Re: Message 37

Travis --

Draw a little picture of Tycho's model of the solar system and see if the perspective from the Earth MIGHT give you phases or not. I think the answer allows you to say that it wouldn't work, as long as you can explain why..

Good luck!

Eric

MESSAGE #38. Wed Sep 22 13:09:10. Saadia-Yael Eisenberg wrote:

Someone informed me via bulletin brd that it will be about the 25 for the Rosh Hodesh-new moon- this is error on my part I ment to say the week next not last. We have a lunar calander and so all our holidays this month (this year's new year etc. ) fall on the end of the week. Who can explain WHY the Moon is often so bright after a storm, is it an optical illusion, is it really just "clearer"??Also what would be a reason NOT to look at the moon when it is brightest and full? We have a custom regarding not doing things by mmonlight and not looking directly at it at certain times of the month. Any comments?

MESSAGE #37. Wed Sep 22 1:09:30. Travis Winn wrote:

I've started doing the third homework but I'm having trouble with problem number 7 on the first chapter. I don't understand how Tycho's model can explain the phases Venus. Can someone help me out with the relationship between the two.

MESSAGE #36. Sun Sep 19 21:22:51. George Morgan wrote:

What's up yall! I hope everyone in our class does well on the ASTRO assignments...and Mr. Hamilton really does answer e-mails..odd...teachers aren't supposed to do that :) But I wanted to give you all this URL:

http://www.bc.cc.ca.us/programs/sea/astronomy/nakedeye/nakedeya.htm

This is an excellent Astronomy source. I want to forewarn you, this page is very big and takes a while to load. If you want more notes from this online book, go all the way at the bottom and click the URL to start at the beginning. Good luck to all on your work, and if you have Internet access problems/PC problems feel free to ask..

MESSAGE #35. Sun Sep 19 19:06:59. Imran Shaikh wrote:

Hello, !!!!!!!!!! I just chacked my grade and i have A+!!!hahaha !!!! thats all for me !!!!!!!

MESSAGE #34. Sun Sep 19 11:51:52. Elisabeth Seasonwein wrote:

Last night the sky was very clear with no clouds in the sky, and I was able to see the moon each time I went outside (at about 10 and 1). It is now visibly over half- full, possibly closer to two- thirds full. The moon had moved across the sky in the west between the times I saw it, and the light was hitting the moon on the lower right portion.

MESSAGE #33. Fri Sep 17 20:09:50. Eric Webster wrote:

Dr. H -- I musta been using some VERRY old html code for that other post. ^{works juuust fine!}

MESSAGE #32. Fri Sep 17 20:08:30. Eric Webster wrote:

let earth=e

sun's radius=100e 1 au = 8600*100e

40au (radius of solar system) = 40*100*8600e

2.5*10⁸ (size of the Milky Way in solar system-size units) *40au=

2.5*10⁸*40*100*8600*e=

2.5*4*10¹⁴*8.6 =

86*10&¹⁵* .1cm =

8.6*10¹⁵ cm =

8.6*10¹⁵ / 100 =

8.6*10 ¹³ m =

8.6*10¹³ / 1000 =

8.6*10¹⁰ km

It's always the little things that trip me up!

MESSAGE #31. Fri Sep 17 19:57:26. Eric Webster wrote:

Katrina you were right! I should have gotten 2.5 * 10 (tenth) km instead of to the ninth power. But who's counting?

MESSAGE #30. Fri Sep 17 19:36:25. Eric Webster wrote:

Dr. Hamilton --

Please modify the posting message boxes to allow html codes so we can use scientific notation on the message boards. I think you can easily exclude the html commands that you don't need or want here.

I just realized that my previous post looks like, well, an asteroid!

MESSAGE #29. Fri Sep 17 19:35:14. Monique Koppel wrote:

Actualy Saadia-Yael, since the begining of the month (a new moon) was about a week ago today it is a half moon (first quarter).It will be another week probably 9/25 when it will be a full moon.

MESSAGE #28. Fri Sep 17 19:33:33. Eric Webster wrote:

I am assuming we are beyond the statute of limitations for homework discussion! Katrina answered size of the Earth-as-a-.1cm-bb-sized Milky way, and her answer and mine differed by a factor of 10. She used algebra (something I am loathe to do) to arrive at her result, so I am using algebra here to see if she might confirm my results

let earth=e

sun's radius=100e 1 au = 8600*100e

40au (radius of solar system) = 40*100*8600e

2.5*10&sup8 (size of the Milky Way in solar system-size units) *40au=

2.5*10&sup8*40*100*8600*e=

2.5*4*10&sup14*8.6 =

86*10&sup15* .1cm =

8.6*10&sup15 cm =

8.6*10&sup15 / 100 =

8.6*10 &sup13 m =

8.6*1013 / 1000 =

8.6*10 &sup9 km

which is what I got. Can someone take me through a process that works differently, and better?

MESSAGE #27. Fri Sep 17 16:58:49. Ambreen Ilyas wrote:

Hey does anyone know how you can tell from which parts of the earth would the solar/lunar eclipses be visible when they occur?

MESSAGE #26. Fri Sep 17 13:59:34. Saadia-Yael Eisenberg wrote:

Yesterday night around 9pm the moon was extrememly bright, as the clouds cleared it seemed very clear for a while. The Vilna Goan produced a chart of predictions hundred yrs ago for the exact moon movements down to the minute. Since our Jewish calander is LUNAR based we use the moon for setting all our time oriented rituals. Thus I am predicting that about friday-saturday next there will be a full moon, since last week was our New Year and new month.

MESSAGE #25. Thu Sep 16 22:43:37. Agnes Lee wrote:

Hey! The moon's waxing! =) The other day, I saw a crescent moon and today it looks like a half moon. It's neat because sometimes you can visualize the full moon or even see its craters...

MESSAGE #24. Thu Sep 16 18:17:34. Eric Webster wrote:

In response to:

>>MESSAGE #22. Thu Sep 16 17:00:36. Lauren Klein wrote:

>> Hey does anyone in ASTRO100 know how to do Essay 1 question 1? I'm a >> little confused.

Lauren see pg. 64 (in the new edition, anyway), Planetary Configurations. Does that help? Or you can pop the cd in the cd-rom and take a gander.

Floyd is preventing me from even basic observations of the moon etc...

MESSAGE #23. Thu Sep 16 17:36:29. Saadia-Yael Eisenberg wrote:

While walking to shul for maariv the other night, I told my friends the quite logical method for determining the spherical shape of the earth (as opposed to being flat). So earth's shadowing the moon leaving a curved shadow made them feel even closer to the moon, metaphysically speaking, suddenly logic and science met and made sense to the average non-science major. Anyone in our class frum and care to explain the "zemanim" -thousands year old Jewish calander system which is lunar based?

MESSAGE #22. Thu Sep 16 17:00:36. Lauren Klein wrote:

Hey does anyone in ASTRO100 know how to do Essay 1 question 1? I'm a little confused.

MESSAGE #21. Thu Sep 16 16:57:38. Leah Goldfine wrote:

Hello Astronomy People! Maybe it's just me, but is there anywhere in the book that tells how to do #7 on page 13? If anyone can tell me where to look or give me a short explanation of how to do the problem, I would greatly appreciate it. Thanks!!!

MESSAGE #20. Thu Sep 16 14:36:39. Patrick Humphries wrote:

Does anyone know if you can see mars in the west at dawn, Question 4 on page 66?

MESSAGE #19. Wed Sep 15 16:20:06. Ambreen Ilyas wrote:

Hi, I tried to look for some stars last nite, that are suppose to form a triangle(according to the sept star map that we received in discussion) and they were Vega, Altair and Deneb(i think). I actually do think that I saw them making a triangle. But its pretty hard to tell since there are so many stars in the sky. Could anyone or Professor Hamilton let me know how I could be sure that I really did see those stars or not. I mean is there a "specific" way in which we use the star map or something? Thanks.

MESSAGE #18. Wed Sep 15 8:28:53. Prof. Doug Hamilton wrote:

Has anyone been watching the Moon over the last couple of days? Last night, the Moon was visible as a thin crescent in the evening toward the direction of sunset. The night before that it was even thinner and even closer to the Sun.

Last night the Moon came to me in a vision and said "I feel neglected. Go out and tell the masses to pay some attention to me!" There are almost 200 people in ASTR100 and you are the only masses that I know, so I need your help!

What I'd like you to do, if you are interested, is to occasionally report here on the ASTR100 Bulletin Board how the Moon looks. With so many people in this class, we can probably have a new observation of the Moon posted every few days - maybe even every day. Then, as a class, we can watch the Moon go through its motions across the sky and through its cycle of phases.

Here are some things you can note about the Moon. What is its phase (thin crescent, thicker crescent, half full, between half full and full, full Moon)? Where is it in the sky (close to the Sun, far from the Sun, near sunrise, near sunset)? What time was the Moon visible (daytime, early evening, midnight, early morning)?

MESSAGE #17. Tue Sep 14 14:09:50. Saadia-Yael Eisenberg wrote:

I am a new student returning to university after over 20 yrs. I have very limited math and science background. Is anyone in the astro100 class interested to help tutor -one on one- once a week to go over briefly the math-physics parts we cover in class/book?

MESSAGE #16. Tue Sep 14 8:10:01. Jonathan Chin wrote:

page 52 thought questions problem 1: i was wondering if anyone could help me with the location of the north celestial pole as related to Australia.

MESSAGE #15. Tue Sep 14 7:45:15. Jonathan Chin wrote:

disregaurd the last message...i was looking at the wrong problem sorry.

MESSAGE #14. Tue Sep 14 6:57:45. Jonathan Chin wrote:

im having problems on number 9 on page 13...... are you supposed to add the exponents or multiply them?

MESSAGE #13. Mon Sep 13 18:20:18. Katrina Martinez wrote:

Response to Message #6: For Problem 3, I did not have to convert from centimeters to kilometers because I dealt with ratios instead of actual numbers. For example, what is the ratio between the Earth and the sun and the sun to the Milky Way Galaxy? For Problem 7, you have to go to the link "Computer Programs," then "Astronomical Distances," then "Let's Go!" The next page prompts you to type in a certain speed. Use the speed from problem 7.

Response to Message #5: The number is big, but not as big as compared to most astronomical units. You can check your answer on the web page (see the extra credit problems).

MESSAGE #12. Mon Sep 13 16:54:52. Eric Webster wrote:

Darn Satellite Viewer. Says moons can't load security code violation error. I will try from school on the WAM workstations. FWIW, I am running MacOS 8.1 on a Power Computing box. Isn't Java supposed to be platform-independent? ;)

MESSAGE #11. Mon Sep 13 16:50:37. Eric Webster wrote:

Lavon in Post #9 asks how to convert metrics. There is a guide in the book, but it basically works like this.

mm = millimeter

m = meter

km = kilometer

1mm = 1/1000 m

1m = 1/1000 km

How many mm in a km? Sounds like a good application of scientific notation to me!

MESSAGE #10. Mon Sep 13 16:46:45. Eric Webster wrote:

In response to Tamara's Post #5 (Problem #7 of the Intro), just make sure you convert back to a time-measurement from the huge number you got. Light travels pretty darn fast even if it has to go all the way to Pluto!

MESSAGE #9. Mon Sep 13 16:26:26. Lavon Hooker wrote:

Hi my name is Lavon H.

My Question is about HW#2 problem 3 about the size of a BB how can i convert this .1 centimeter radius to kilo..I need help...I am DUM..I cant get it!!!Please help....Thank You 8)

MESSAGE #8. Sun Sep 12 22:33:35. Shannon Maycher wrote:

I just wanted to know if there was any format to the homework assignments. For example if they need to be typed or handwritten. I also have questions about problems 3 an 7 on the introduction, besides these comments all is well on the Astro homefront. The next open house is on Monday the 20th exactly a week from tomorrow!

MESSAGE #7. Sat Sep 11 18:47:31. Prof. Doug Hamilton wrote:

David asks a good question in Message #4. The outermost moons of Jupiter and Uranus are on orbits that cross one another!

First, realize that the orbits of the satellites are actually inclined relative to the planet's equator - so the orbits are in 3D and need not actually intersect. But the orbits will evolve, and the will periodically intersect. Then it is possible for the satellites to collide! But the satellites are small and space is big. If we calculate how it should take, on average, until a collision, the answer is 5-15 billion years! This is older than the age of the Solar System, so they haven't had enough time to collide yet!

If anyone else has problems viewing the java applets - let me know here what configuration you are using (e.g. A PC with Windows 95, and netscape).

MESSAGE #6. Sat Sep 11 15:10:13. Courtney King wrote:

I am working on the homework for Friday September 17th and am having a difficult time with the problems for the introduction. Specifically on number three do you convert centimeters to kilometers for the first part or vice versa and for number 7 how do you check your answer with the web page addressed in the first extra credit?

MESSAGE #5. Wed Sep 8 20:11:49. Tamara Smith wrote:

I would like to know if anyone else got a really big number for the answer to problem7 of the introduction. The answer I got seems like a really big one, and I just wanted to double check and make sure that I wasn't headed in the wrong direction.

MESSAGE #4. Wed Sep 8 17:00:46. David Moyer wrote:

In response to Eric (post #3) I got the applet to load just a few seconds ago. It could have been a network fluke when you tried, but you may also want to check some of the settings on your browser - under tools/internet options with IE, or edit/preferences with Netscape. If Java is disabled or the security is set too high, it wouldn't download any applets.

Also, Professor Hamilton, I noticed in the satellite Viewer that some of the outer planets had smaller moons with crossed orbits... what's the chance of a collision?

MESSAGE #3. Mon Sep 6 15:34:33. Eric Webster wrote:

Can anyone else get

http://janus.astro.umd.edu/astro/moons.html

to come up OK? I just got a security code violation from the applet..

MESSAGE #2. Mon Sep 6 15:27:10. Eric Webster wrote:

Can someone tell me if we turn in our extra-credit homework to the TA at section, or whether Dr. Hamilton wants to collect them at the lecture?

MESSAGE # 1 . Tue Aug 31 20:35:50. Prof. Doug Hamilton wrote:

Welcome to ASTR 100! I hope that you will use this bulletin board to communicate with other students in the class. You can learn a lot from each other as well as from the TAs and the Prof. And, act now (by posting a message anytime before the end of the semester) and you'll earn a cool 4 bonus points added to your grade at the end of the semester!!

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