ASTR100 BULLETIN BOARD

MESSAGE #69. Wed May 19 11:21:24. Prof. Doug Hamilton wrote:

Garrett asks some good question in MESSAGE #62.

How much of the book will be obsolete in 25 years?

Well, astronomy is changing so fast that ASTR100 books come out with new editions every 2 years! But very little of the material in our book will be proved outright wrong. Partially, this is because astronomers try to be pretty sure of what is going on before putting it in a textbook! But we we will definitely get a more complete view of various topics as further advances are made. For example, ten years ago, we hadn't detected any objects in the Kuiper belt or any planets around other stars. Astronomy books for back then say that the Kuiper Belt is "a theoretically-predicted belt of icy objects out beyond Pluto" and that other sunlike stars "probably have planets circling them like our own solar system." Today's books can make more definitive statements now that we have actual observations of both types of objects.

How close is science to bridging Einstein's relativity and quantum mechanics?

Relativity applies for objects that move very fast while quantum mechanics applies to objects that are really small. When really small objects move fast, our theories can't handle it! The physics right near a black hole is an example of a place where our theories break down. We have only vague ideas of what should happen. Physicists have worked for years trying to come up with a theory that combines relativity and quantum mechanics - so far, without success. Some theories show promise, but my feeling is that we still have a long way to go! It could even turn that we will never find a unifying theory.

MESSAGE #68. Wed May 19 11:00:38. Prof. Doug Hamilton wrote:

I just arranged grading times with the TAs. Here's our plan: Open house papers will be graded and posted by Thursday night. Homeworks will be graded and posted by Saturday. The final exams will take a long time to grade! We will begin working on them tomorrow and will finish up over the weekend. Final section grades, final exam grades, and the final course grade will be posted on Monday.

Jason - I put an extra question on the second midterm by accident which made the exam worth 105 points instead of 100. With the extra credit, a perfect exam would have gotten 108 points.

MESSAGE #67. Wed May 19 6:44:38. Patrick Flores wrote:

Just wanted to wish everybody good-luck on the Astronomy exam!

MESSAGE #66. Wed May 19 3:21:21. Jason Ross wrote:

Hey Proffesor Hamilton, I have a question about the second midterm. I thought the 5 points at the end were extra credit. But you have them added in to out total points. If I am wrong don't worry about it. Have a great summer everyone!!!

MESSAGE #65. Tue May 18 17:49:38. Prof. Doug Hamilton wrote:

OK, here they are ... the long-awaited, much-discussed, and hopefully amazingly-useful final exam hints!!!! Why are they so late?? Well, I just got the exam finished off about an hour ago. You guys aren't the only ones who do things at the last minute sometimes! Actually its my own fault for trying to make up the exam Monday and Tuesday while holding office hours at the same time. Lots of people showed up with lots of questions!

So some hints! First up: the exam is weighted pretty heavily on stars and galaxies (stuff since the second midterm). More than 1/2 of the exam is on this material. The other 40% or so is scattered over the first few months of the course.

The test is significantly shorter than two midterms. So you should be able to finish with plenty of time. There are 50 multiple choice answers and seven short answer questions, some with multiple parts. There is one question that focuses on equations; this question has two parts. Use the extra time to check over your answers carefully!!

A Hint: Answers that include the word "alien" are probably wrong!

A Better Hint: Make sure that you have a good sense of how big things are, and how far apart things are. These are some of the most fundamental properties of objects in astronomy! Having this "framework" will help you make sense of what otherwise must seem like an overwhelming number of isolated facts.

MESSAGE #64. Tue May 18 16:24:16. Jesse Ray wrote:

Prof Hamilton, what about the "short answer question" hints you said you'd post, "early this week"?

MESSAGE #63. Tue May 18 13:28:31. Prof. Doug Hamilton wrote:

Grading is running a little slow right now - remember, your TAs have final exams too!

Over the next several days we'll have a lot to do - homework #8, final section grades, and the last open house papers all need to be graded in addition to the final exam. Try to be patient! We should have most things graded and posted by the weekend.

Garett, I'm going to defer your question until after the final - but check back afterwards!

MESSAGE #62. Tue May 18 2:03:32. Garrett Cooper wrote:

Professor Hamilton, I'm curious...how much of the stuff that is including in our text do you thinkg will be proved obsolete in 25 years? And how close is Science in bridging Einstein's quantum mechanics and quatum theory...what I mean is, how close is science to reach a unified theory...and do you think such a theory is even possible?? Thanks, Garrett Cooper

MESSAGE #61. Mon May 17 19:48:10. Michelle Sutton wrote:

Dr. Hamilton: I turned my open house paper in on the last due date and it is still not showing on the 'What's my grade' page. Have you posted them yet or will you soon. I just want to make sure that you received it.

MESSAGE #60. Sat May 15 16:42:15. Prof. Doug Hamilton wrote:

Let's see ... math problems on the exam. I'll have at least one, but probably two simple math problems on the test. They could be from the early part of the class or from the later stuff. The problems will be similar in style to the ones that I gave on the midterms (see last message for another example). Make sure that you are comfortable with that type of calculation! I won't give you problems where you will need a calculator, and you probably won't need to work with units (at least not anywhere near as much as on the homework sets).

Hints on short answer questions? I'll post some early next week after I've made the exam up!

Homework Solution Sets for #7 and #8 are posted under "Assignments"!

MESSAGE #59. Sat May 15 16:29:14. Prof. Doug Hamilton wrote:

The Alpha Centauri system is composed of three stars, two like our Sun and a third, Proxima Centauri, that is much less massive than the Sun. Proxima Centauri is the one nearest to us currently. We get some light (and some heat) from each of these stars, but it is an incredibly tiny amount. Take one of the sunlike stars as an example. I remember that the nearest stars are 7,000 times further away than Pluto is, and Pluto is 40 times further away than the Sun is. So Alpha Centauri is 280,000 times further away than the Sun. Remember this equation: F= L/4(pi)d² ? If we assume that the Sun and one of the Alpha Centauri stars have the same Luminosity, L, we can use the different distances, d, to solve for the different Fluxes of light and/or heat, F. (280,000)^2 is 78,400,000,000. We get 78,400,000,000 times less light and heat from Alpha Centauri as from the Sun!!

The Sun experiences variations in its brightness that are millions of times larger than the amount of light and heat the we receive from Alpha Centauri. In fact, if a 3km asteroid moved between the Sun and the Earth, it would cause a larger variation!

MESSAGE #58. Fri May 14 10:53:06. Jennifer Plopa wrote:

I was just wondering if the Earth recieves any heat at all from its nearest neighbor star Proxima Centauri?

MESSAGE #57. Fri May 14 10:44:28. Katrice Leach wrote:

Dr. Hamilton. Are the problems on the exam going to be more from this last section of the class or should we know how to do mathematical problems from the first half of the class also?

MESSAGE #56. Fri May 14 10:32:34. Jason Ross wrote:

Hey Professor Hamilton.

On our final, I know that you are giving us any equations that we need. But will we need to know the Units of the answer to the equations. Also could you give us a few hints on what the short answer questions will be.

Thanks Jason Ross.

MESSAGE #54. Mon May 10 15:39:08. Prof. Doug Hamilton wrote:

QUESTION 1: Written as a formula, Hubble's law looks like this: "V = HD" where "V" is the speed that the Galaxy is moving away from us and "D" is its distance from us. The constant "H" has bizarre units (see page 486 of the book) - don't worry about the units though! The important thing that Hubble's law tells us is 1. that all distant galaxies are moving away from us and 2. that further galaxies move away from us faster. In fact if galaxy A is twice as far away as galaxy B, Hubble's law tells us that galaxy A is moving away from us twice as fast as galaxy B is.

Nearby galaxies do not obey Hubble's law. Why? Well, first that is simply what observations of galaxies tell us: Hubble's law is observed to work only for distant galaxies. We can understand that observation by realizing that nearby galaxies are strongly tied together by their mutual gravity which keeps them from flying apart.

QUESTION 2: The Sun's magnetic field gives rise to the solar wind which can influence the upper atmosphere of the Earth (especially by creating auroras). Some people have argued that it can affect Earth's weather, but this is still controversial! It probably has a very small effect, but certainly is NOT responsible for noticeable large-scale weather patterns like el Nino and la Nina. The most important forces shaping Earth's weather are: 1) the Earth's rotation (this leads to spinning storm systems like hurricanes and tornados, and also the jet stream) and 2) solar heating (differences in temperatures drive strong winds).

MESSAGE #53. Mon May 10 10:53:25. Nisha Amin wrote:

Hi Dr. Hamilton I have a question about the Hubble law. First one is what has gravitation force got to do with the nearby galaxies and the units of Hubble constant (when using the formula to find the velocity), because it said in one of the chapters that hubble law just holds for far away and not for nearby galaxies. My second question is that I know Sun's magnetic field has something to do with the changes in the climate on the earth , but then how would that explain el nino and el nina. Is it the sun's gravity that causes this changes. I confused on this two things. thanks nisha

MESSAGE #51. Thu May 6 13:53:05. Prof. Doug Hamilton wrote:

Hi Keisha,

Two bonus points for anyone who posts a message to the webpage! (You can only earn this once though!). Maybe we'll have some lively discussion here as the semestere winds down ....

MESSAGE #50. Wed May 5 11:03:21. Prof. Doug Hamilton wrote:

OK, here we go with the blue sky answer! Sorry to take so long with this. This was one of the coolest things I learned in my first college physics class.

The sky is blue because of the way that air molecules scatter light. The Earth's atmosphere does a great job of scattering light - if light didn't scatter, all sunlight would come straight from the Sun and the sky would look black in all other directions. This happens on the Moon which has no atmosphere. On Earth, when you look up in the sky away from the Sun (don't look at the Sun - you'll fry your eyes out and die in agony!), you are seeing light that has come from the Sun and then been scattered off an atmospheric molecule, changing its direction of motion to come to your eyes.

Now, if the scattering objects (the air molecules) are smaller than the wavelength of light, then short wavelength blue light is scattered more efficiently than long wavelength red light. This type of scattering is called Rayleigh scattering. Since we are seeing scattered light when we look at the sky, the sky looks a lot bluer than sunlight.

So where is the red light? It is scattered too, but not as much. You see it when you look close to the Sun. This is especially noticeable when we look at the Sun near sunrise and sunset where the sunlight has to travel at a shallow angle through lots of Earth's atmosphere. The sky near sunrises and sunsets look distinctly red.

Small dust grains or water droplets can also scatter light like this. Sunsets are often even redder after volcanic eruptions blast lots of dust into our upper atmosphere. Also, note that the dust in the Milky Way galaxy causes stars to appear fainter and redder than they actually are for exactly the same reason given here.

MESSAGE #49. Wed May 5 10:39:43. Prof. Doug Hamilton wrote:

Reminder about the LAST open house!! This meets tonight at 9:00 pm. Follow links from the "Course Description" for more information. DON'T blow this off!

Sara - I don't have email for you. We haven't been able to locate your open house paper. Please come see me and bring an extra copy of your paper.

MESSAGE #48. Tue May 4 14:54:48. Sara Stoner wrote:

This is in response to a question from a while back, but I think I have some idea of why the sky is blue. I'm pretty sure it has something to do with the water in the atmosphere diffracting or reflecting the light from the Sun. I guess this would also explain why the oceans (minus the pollution) are blue. So, Hamilton, am I right?

MESSAGE #47. Wed Apr 28 13:42:56. Keisha Stewart wrote:

Ohh?? I forgot to ask. Do we still get extra points for posting a message??? I obviously need all the points I can get.

MESSAGE #46. Wed Apr 28 13:41:21. Keisha Stewart wrote:

I'm having a very difficult time in this class, especially on the exam II (which was supposed to be "easier" than the first one). I got the exact same score, except this time I got an additional point for getting the extra credit (and I even studied more this time and used note cards).

But enough venting, I'm a little behind. I'm still on Chapter 12 because it's more difficult for me (being that I'm a senior journalism major and by this time, math and science deficient). Can someone give me any tips for remembering and applying these formulas in Chapter 12?? Or maybe some kind of word game I can play with myself to remember the whole point of the equations??

MESSAGE #45. Tue Apr 27 14:01:46. Prof. Doug Hamilton wrote:

I'll be away this week, but will return to discuss why the sky is blue early next week!

In the meantime, is anyone else finding any new Solar Systems out there?

You might be interested in a new tool "The Satellite Viewer" which allows you to watch a planet's moons as they orbit. Take a look at http://janus.astro.umd.edu/solarsystem.html and let me know what you think!

MESSAGE #44. Mon Apr 26 1:35:48. Tomeka Reid wrote:

I think some people have a little too much time on their hands. Anyway, so Dr. Hamilton, or anyone, can you answer Kenneth's question about why the sky is blue?

MESSAGE #43. Thu Apr 22 11:28:16. Darryl Butler wrote:

So I dont get kicked out of this school for plagiarism, some or maybe all of my discoverings can be found in Kathy Sawyer's Washington Post article. Which means that I may not be the first one to have made the discovery of this new solar system, but i still new it before a lot of you so thats all that matters. However I would still like to have an explanation as to why we have not discovered something this big until now.

Sincerely your friend DJ Butler

MESSAGE #42. Thu Apr 22 11:20:08. Darryl Butler wrote:

Hey Guys guess what! The other day when i was doing my extensive Astronomy research outside of lecture, I stumbled across a new solar system .. Yes, I new solar system. Now you all probably think that i am on crack like that guy Gregg Aronson, in which I have no relation to whatsoever, but it's true. There is a new solar system in our universe. The new solar system is made up of I think 3 planets and they revolve around this one star, which to my knowledge has not been named yet so Im going to name it first as "Chonco". This star, Chonco, has a very high flux, which means that if you arent blind then you can see it with the naked eye. If you thought that the sun was hot then Chonco is the mad oven torch, and it's just a kid compared to our old fart of a sun. I am the first to discover this new Solar System! On to these planets that i have discovered. All three of these planets seem to revolve around Chonco. But the weird thing about it is that the one closest to it seems like it is really close to it. It probably revolves around Concho in like 5 days. The other planets aren't too far away sorta like the distance from our sun to Mercury or Venus. The bottom line with my new discovery of the solar system is a few things. #1 .. Im better than you. #2 .. All if this stuff that these stupid astronomers have been studying for the past I dont know how many years is just not accurate. I THOUGHT THERE WERE ONLY 9 PLANETS IN THE UNIVERSE DIPSTICK! Nope there are 12 and counting. And I found them! and #3 .. I want my grade to be changed on every exam that Ive taken cause I found the new solar system which means that I must be more right than anyone else, so my grade has to be better than everyone else right? Ok, Ive written enough here. Lastly I would like to say that I dont blame everyone for not being able to locate this new Solar System. It takes lots of observation and many ASTRO skills to get this type of 411. So if you all have questions then direct them to me cause i found the new solar system.

Oh yeah and my question: What is the deal with this new solar system Hamilton? How come nobody discovered this before me? I mean these planets are huge like 3 times the size of Jupiter

MESSAGE #41. Sat Apr 17 11:40:21. Gregg Aronson wrote:

Howdy Yall. First of all Ide like to appologize for my conduct concerning my last message. I realized well after the message was sent that I took advantage of Prof. Douglas Hamilton's services in promoting my own cause. Due to my horrible judgement and disrespect of Prof. Douglas Hamilton, I have decided that I just dont deserve to be on Earth anymore. Thats ok though, because I have found a way to redeam myself and prove my worth as a human being. I have decided to take the big trip...you guys know what trip Im talking about. The BIG TRIP. Ya, that one. The one into space designed to find those silly other civilizations. So heres the deal...they're looking for a few good humans who dont really have much value on Earth(thats what they think-Ill show them, you just watch man!!! I WILL!) to send off into space and make friends with whomever we encounter. Now I can be a friendly guy, if I really, really, really, really try, and I know some stuff about astronomy, I mean I am Prof. Douglas Hamilton's student and anyway whats there to know?...you got your crazy little escape velocity there and you throw in a little Roche limit gravitational pull and your all set, also Im pretty good at drinking, and I can make a mean grilled chease, and last but not least of my many impressive qualifications I can sleap through classes like nobody else. So, I think its obvious that Im over qualified for the job, so when the ballots come out, remember VOTE ARONSON for Space Alien Finder and Talker Toer. You will not regret it. DAMN IT. Ive done it again. Ive abused the power. Forget it, I resign. Oh ya, so as for my astronomy question...Do you guys think that there is an end to space or just never ending emptyness? Also, when we do encounter those cute aliens, do you really think they will look like they do in the movies? I mean I think its kinda arrogant of us to think that they would look like us only in gray or something. Personally I think they will all be wearing Mets hats and wifebeaters that say "wine em, dine em, 69 em." But thats just my opinion. So please accept my apology. I beg of you. Love Gregg Aronson

MESSAGE #40. Sat Apr 17 0:05:25. Gregg Aronson wrote:

Well well well....Here we are again. I actually had the honor of speaking with Prof. Douglas Hamilton personally today, and let me tell you it was the single most exuberating experience of my entire life. I even got his autograph. I bet none of you guys have his autograph....well nananebooboo....I did. Ok so lets talk some serious astronomy here. The other day I was looking up at the sky and I realized that the single most important thing in life is to find another civilization. But what also crossed my mind was a real problem. What could we possibly say to them that would interest those freaky green guys at all? Also, who would speak on our behalf? Personally I think I would do a fantastic job. So this Bulletin message isnt really a question, its more like a campaigning tactic. VOTE ARONSON for Alien Communicator Guy Type Thingy Position. I hope you guys know that we have already estabolished contact with an alien civilization and the government is hiding it from us. Personally I think they just want to hog all the fun. I have a friend on the inside named DJ butler so thats how I know all this secret stuff. Pretty cool huh. So if you also think there are aliens out there and you want a down to Earth guy like me to represent our planet.....remember vote Aronson for Alien Communicator Guy Type Thingy Position!!!!!!! You wont regret it. I mean I wont make a fool of our species.....I swear. Ill do good. What? You guys dont think I can do the job? Well you try drinking 12 beers everyday and acting civilized. Its damn tough. Fine forget it...I resign. You guys want Douglas Hamilton dont you. Well thats about all the disapointment I can take for one night. So until next time kids, remember..... ZBT Rocks!!! Love Gregg Aronson

MESSAGE #39. Thu Apr 15 22:07:30. Yue Cao wrote:

just thought this might be fun.. here is the list of short answer question I guess would be on the exam.. 1) why are the inner planet much smaller than the outer planet and they density is much higher. 2) some kind of picture of comet, identify the parts, ie. neucleus, coma, dust tail, gas tail. 3) a calculation question on either E=mv^2/2 (similar to the homework problem) or escape velocity of one of the planet (I doubt this though, since we are not allowed to use calculator, it's kind hard to much easy numbers for this one, the kenetic energy one is more likely). 4) question about Jupitor, like what's the Giant Red Spot (Coriolis effect, atmospheric vortices), and why is Io still active (tides). 5) how does planet form rings (Roche limit), why r there gaps in Saturn's ring, (resonance). 6) why is Venus so much hotter than Earth and earth is much warmer than Mars even though their distance to the Sun doesn't differ that much. (atomsphere, green house effect). 7) why are neptune and Uranus seem rather featureless compare to Jupitor and Sature (they self rotation is much slower, not much wind).

and there is going to be a lot of multiple choice questions on what's the biggest, smallest, longerest day, longerest year, hottest, most massive, ...

the above are just my guess, hopefully intelligent ones and close to what Dr. Hamilton's view. ^_^. good luck to us all..

Jason

MESSAGE #38. Thu Apr 15 19:34:54. Prof. Doug Hamilton wrote:

More Exam Hints!!

The test has 25 multiple choice questions and seven short answer questions. Two of the seven question have a part a) and part b).

There is one question which involves an equation.

I think that the exam is a little easier than the last one! Some of the multiple choice questions have only 4 choices, so it is a little easier to find the correct answer.

Good Luck Tomorrow!!

MESSAGE #37. Thu Apr 15 11:34:08. Prof. Doug Hamilton wrote:

Hi Angela - sorry that no one came through for you on HW#6!

Kenneth, I'll be happy to give you an explanation for why the sky is blue, but I'd rather another student try to explain it first! Can anyone help?

EXAM HINTS!!! (as promised)

I will not emphasize the chapter on the Sun as much as the other chapters (no short answer questions on the Sun, and only 2 or 3 multiple choice questions). I'll ask only about the simple but important points, and I won't ask about the details of the solar cycle which is pretty complicated!

I'm making up the exam right now, so stay tuned for more hints!!

MESSAGE #36. Wed Apr 14 20:26:23. Kenneth Wood wrote:

I have heard many stories about why the sky is blue. Maybe someone can help me clarify what I have been hearing. I have heard so many things, but none sound true. If not another student, Dr. Hamilton can you explain this?

MESSAGE #35. Wed Apr 14 20:25:31. Kenneth Wood wrote:

I have heard many stories about why the sky is blue. Maybe someone can help me clarify what I have been hearing. I have heard so many things, but none sound true. If not another student, Dr. Hamilton can you explain this?

MESSAGE #34. Mon Apr 12 17:32:00. Angela Bettick wrote:

I am looking at the homework, and i do not understand how to go about starting problem 1 from chapter 9 and problem 3 from chapter 10. i am also confused about how to convert to different units. can someone help asap? thanks, angela

MESSAGE #32. Fri Apr 9 13:20:02. Prof. Doug Hamilton wrote:

Karla asks a good questions about moons, and Gregg appears to have been drunk by 5:20 last Friday afternoon!

It turns out that the book is wrong on the number of moons for both Saturn and Uranus. Saturn and Uranus have 18 and 17 known moons, respectively, (as I said in class) -- not 22 and 15 as stated on Arny page 221. For Uranus, the discrepancy is clear: two new moons of Uranus were discovered in 1997! Actually, two of the discoverers of those moons were my thesis advisors at Cornell! Arny noted the discovery in a footnote on page 221, but forgot to increase his number of Uranian moons by two. I don't know where his 22 moons of Saturn came from though - it's just wrong!

On the exams, I won't ask you exactly how many moons the giant planets have, since these numbers will probably increase in the future as new moons are discovered. How moons formed, and some of the details about the more famous ones are fair game, though!

MESSAGE #31. Fri Apr 9 11:47:59. Karla Cabrera wrote:

Dr. Hamilton:

I have a small doubt about the number of moons that some of the Jovian planets have. In the book on page 221, it says that Saturn has 22, and that Uranus has 15. However, in the notes I took in class on March 19th, you said that Saturn has 18 moons and that Uranus has 15 (chart). Which inofrmation is correct and which information should I know and memorize for the exam? Thanx.

Karla Cabrera Sect 204

MESSAGE #30. Fri Apr 9 11:47:12. Karla Cabrera wrote:

Dr. Hamilton:

I have a small doubt about the number of moons that some of the Jovian planets have. In the book on page 221, it says that Saturn has 22, and that Uranus has 15. However, in the notes I took in class on March 19th, you said that Saturn has 18 moons and that Uranus has 15 (chart). Which inofrmation is correct and which information should I know and memorize for the exam? Thanx.

Karla Cabrera Sect 204

MESSAGE #29. Fri Apr 2 17:20:08. Gregg Aronson wrote:

Oh my lordy lord lord...I dont believe Im actually on Prof. Douglas Hamilton's World Wide Web Page!!! Do you guys know what that means? It means EVERYONE in the entire world can check it out. How rad is that? I mean never in my entire life have I ever encountered such an incredible concept. I think I have to lie down. Really though, I do have a question, and a darn good one at that. My question is.......If the universe is made up of like kazillions of planets and solar systems and galaxies and super clusters and stuff, then why dont we just use them as our land fills? I mean who cares if we dump all our trash into space? Not me! And if there are like other civilizations who get realy pissed and try to destroy our planet and take all of our women and children, thats fine with me. I mean Im single and I dont have any kids, that I know of. And anyway, it would be cool to see the crazy lookin fellas get all worked up. Plus we have the atom bomb right? So what are we afraid of? Love Gregg Aronson

MESSAGE #28. Thu Apr 1 12:54:08. Prof. Doug Hamilton wrote:

Homework #5 is due tomorrow before class!

MESSAGE #27. Sat Mar 20 18:37:56. Prof. Doug Hamilton wrote:

At 8:46 tonight it is officially Spring! The Sun will be directly above the equator then, and it is heading north.

MESSAGE #26. Fri Mar 19 10:55:09. Prof. Doug Hamilton wrote:

For info on the Open House, follow the "Course Description" link from the main page and then the link under the "Open House" section. There is a shuttle schedule there too.

MESSAGE #25. Thu Mar 18 23:14:07. Timothy Wendland wrote:

Does anybody know what the Open House topic will be for this Sat. at the observatory, I have not had an opportunity to call the dept. and are only students permitted to attend or can anyone go?

MESSAGE #24. Wed Mar 10 20:33:44. Courtney Britt wrote:

I'm confused about the diffraction problem as well. As I saw it, D=0.5 cm, Wavelength=500nm, but how do we estimate the arc length of the 1mm space??

MESSAGE #23. Wed Mar 10 14:31:06. Prof. Doug Hamilton wrote:

Amit Chandok has rescheduled his office hours which were cancelled yesterday due to snow. His office hours this week will be from 4-6pm Thursday in CSS 0224. The review session for Monday's midterm will start immediately afterwards t 6:00pm in the physics lecture hall.

MESSAGE #22. Mon Mar 8 11:04:37. Nidhi Sarin wrote:

does anyone know how to do problems 2 on page 115 and 174?

MESSAGE #21. Sun Mar 7 18:55:02. Jason Robshaw wrote:

I am a little confused! Is the resolving power formula the same as the defraction theory? If so, how do you figure out arc seconds with the information given in Question 2, Problems, Page 175.

MESSAGE #20. Fri Mar 5 10:13:45. Prof. Doug Hamilton wrote:

I forgot to mention in class today that there is another open house tonight! Take a look at ths syllabus for more information.

Response to MSG #19: The problem is that I've set up the web site so that many different classes - not just ASTR100 - can use the scientific notation page (and the other tools as well). Some other classes at other colleges even use my site. It is not easy to have links that send you back to where you came from! There are some things that I can do to make this easier though - I'll look into it.

MESSAGE #19. Fri Feb 26 2:00:07. Samuel Smith wrote:

It would be nice if there was a link that would take you from the scientific page back to the home back. If not then you have to keep clicking the 'back' button. Just a suggestion.

MESSAGE #18. Wed Feb 24 21:59:42. Angela Ricciuti wrote:

I am not sure if this hint is correct but I believe the answer to problem #4, on homework #3, can be find on page 46. Look at Kepler's third law and it shows an example of Pluto. We have the answer of the alien's planet being 4 times further away. BE CAREFUL, I AM NOT SURE IF THIS IS CORRECT! This is how I solved the problem though.

MESSAGE #17. Tue Feb 23 19:27:21. Michelle Sutton wrote:

Does anyone understand what problem 5 in chapter 2 means? Do I have to solve the moon and earth's escape velocity and then put them into a ratio?

MESSAGE #16. Mon Feb 22 14:29:34. Nidhi Sarin wrote:

hi, i was wondering if someone who understands how to do #4 on homework #3 could explain how to go about doing it.

MESSAGE #15. Mon Feb 22 14:28:10. Nidhi Sarin wrote:

hi, i was wondering if someone who understands how to do #4 on homework #3 could explain how to go about doing it.

MESSAGE #14. Thu Feb 18 20:05:20. Prof. Doug Hamilton wrote:

You can check some of the answers that I've given here by watching the sky! The Moon is a thin crescent, visible in the evening just after sunset right now! Watch over the next two weeks (a little less) as it becomes more and more full and sets later and later in the evening.

MESSAGE #13. Thu Feb 18 19:57:22. Prof. Doug Hamilton wrote:

Answer to Msg. #2. Maybe this question was too hard! Or not interesting enough? Anyway, here's the answer.

For the Moon to be a thin crescent, it must be almost between the Earth and the Sun like this (distances are inaccurate!): S M E. Why? At all times, exactly half of the Moon is in sunlight. So if we see only a thin lit crescent from Earth, most of the sunlit part of the Moon must face away from Earth. This occurs only when the Moon is nearly between the Sun and the Earth.

So answer A is correct: the Moon is closer to the Sun than the Earth is. Since the Sun and Moon are nearly in the same direction as seen from Earth, they will set just a few hours apart. Since the crescent Moon is visible at sunset, it must set soon: answer B is correct.

Finally, the Moon is full when the Earth is roughly between the Sun and the Moon, i.e. the object are in this configuration: S E M. The Moon takes about 4 weeks to go around the Earth, so it takes about two weeks to go from new Moon to full Moon. It takes just a little less time because it is just after new Moon (You need to draw a better picture than I can here to show this - Try it!). So answer F is also correct. All other answers are incorrect.

Correct answers are: A B F

MESSAGE #12. Mon Feb 15 15:25:32. Joseph Simons wrote:

Dr. Hamilton, I was wondering if you could put up the answers to the problem you posted last week, since I've noticed that no one has tried to answer it yet. I got D & F, but I'm sure I'm wrong. Thanks.

MESSAGE #11. Sun Feb 14 14:27:23. Yue Cao wrote:

p13, distance from Sun to Pluto 40 AU, 1 AU=150million km.

MESSAGE #10. Sun Feb 14 12:51:47. Kevin Marchbanks wrote:

Does anyone know the distance from Sun to Pluto?

MESSAGE #9. Sun Feb 14 11:14:01. Yue Cao wrote:

hi, Anyone has trouble understanding the last question in the homework? I just don't know what they mean by "if a planet is at opposition ..." ^^^^^^^^^^^ what does it mean opposition in space? Can anyone tell me, thank you very much!

Jason

MESSAGE #8. Sat Feb 13 15:40:55. Prof. Doug Hamilton wrote:

Response to Message #5 from Angela Ricciuti. On Feb. 6, the Moon was just over 1/2 full, and it didn't rise above the horizon until 11:45pm. So unless you were out looking for it after midnight, you wouldn't have seen it!

Today the Moon is just before new Moon. It won't be easily visible for another week or so because, as seen from Earth, the Moon is roughly in the direction of the Sun. The Moon will become visible at the end of next week just after sunset. It will first appear as a very thin crescent near where the Sun dips below the horizon. With each passing day, the lit part of the Moon will become larger, and the Moon will set later and later. Watch for the Moon in the evenings just after it gets dark! You can see its phase and position against the stars change from one night to the next.

MESSAGE #7. Sat Feb 13 13:46:20. Jesse Ray wrote:

Hi. Does any one know why the Zodiac is divided into 12 signs, (thought questions # 3, page 52), my guess is that it has to do with the fact there are 12 months in a year, so by having 12 signs you could use the sky as a kind of calender, but that's just a guess. Did anyone remember reading it in the book or hearing something in lecture? Andrea Jordan, I think question for review #1 meant the same thing as the book illustrates on page 12, figure I.10.

MESSAGE #6. Fri Feb 12 18:13:17. Andrea Jordan wrote:

Hi. I was wondering if anyone understood Questions for Review #1 from the Introduction. It asks for the systems that the Earth belongs to. What systems are they talking about? Are they talking about systems as in planets or the Universe as a whole?

MESSAGE #5. Thu Feb 11 10:07:32. Angela Ricciuti wrote:

I was wondering if anyone noticed on Saturday, February 6, there was no moon outside. I was wondering if I was just not in plain view from all the houses in my neighborhood or was there a cause for me not seeing the moon. Does anyone know?

MESSAGE #4. Thu Feb 11 0:44:58. Angela Bettick wrote:

Hey everyone, just thought i'd reming you that tomorrow, Feb.11,1999, at 10:07 AM, Pluto will return to being the furthest planet from the sun.

MESSAGE #3. Wed Feb 10 12:25:40. Terry Gray wrote:

If you are having trouble figuring out how scientific notation works, do the extra credit problems for homework 2. The problems are easy to figure out and you can do as many as you want, without anyone knowing how you did.

MESSAGE #2. Mon Feb 8 15:51:24. Prof. Doug Hamilton wrote:

In order to encourage class participation on this site, I'll credit you 2 extra credit points at the end of the semester if you post a well-reasoned message (question, answer, etc.) on this bulletin board at least once during the course of the semester! What I want to encourage most is that you use this page as a way to communicate with other students in the class. You can learn a lot from each other!

Here's an Earth-Moon-Sun question to get you started. It requires visualizing the relationship between the three bodies. Try drawing a picture!

You see a very thin crescent moon in the evening just after sunset, which of the following statements is true right then? Why?
A. The Moon-Sun distance is smaller than the Earth-Sun distance
B. The Moon will set in just a few hours
C. The Moon is at its highest point in the sky
D. The Moon will be visible all night
E. The Moon will be full in about 5 days
F. The Moon will be full just under two weeks
G. The Moon will be full in just over two weeks
H. The Moon will be full in just over three weeks
I. There will be a solar eclipse soon
J. There will be a lunar eclipse soon
K. The Moon will slam into the Earth and blast it to pieces


This is much harder than the typical questions that I will ask on exams, because there are lots of possible answers and more than one of them is correct! It is a good question for discussion, though. Can you argue that one of the answers has to be right (or wrong?)?

MESSAGE #1. Sun Feb 7 0:34:02. Prof. Doug Hamilton wrote:

HOMEWORK #2 CORRECTION: The questions from the Introduction are on page 13.

HINT for Intro, problem 7: The speed of light in meters per second can be found in the Intro. Convert this to km per second (km/s) using the fact that there are 1000 meters in a kilometer. Now you'll need the distance from the Sun to Pluto in kilometers. Use Table 1 and the definition of the AU from problem 2.

Remember to turn the homework in at the BEGINNING of class Monday Feb. 15! No credit is given for late homework!!

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