ASTR430 FALL 2009 BLOG

MESSAGE #77. Sat Dec 26 11:45:15 2009. Prof. Doug Hamilton wrote:

Forgot to mention - Ice the Prof photos are available on the ASTR430 website! Thanks again for taking ASTR430 and best wishes for next semester.

MESSAGE #76. Sat Dec 19 11:08:50 2009. Prof. Doug Hamilton wrote:

We had one last minute change-of-mind, but 7 brave final takers remain!

Here is the final exam. Ignore the "120 minute in class" phrase - I left it there because this is exactly the same final that you would have had in class.

Please send me an email after you finish with:

• 1) the four hour block of time that you used
• 2) the final, or a note as to how you will get it to me.
• 3) any thoughts about the exam's difficulty

Given that there are only 7 of you, I think that I would prefer the scan+email option for those of you that can! A fax or dropping it under my door for those of you on campus is my second choice. And, if you absolutely must, a hardcopy in an envelope postmarked Monday.

Good Luck everyone! And thanks for being patient at this unusual end to a very enjoyable semester!

MESSAGE #75. Sat Dec 19 10:35:31 2009. Prof. Doug Hamilton wrote:

Final Takers: Jeremy, Kate, Geoff, Jena, Sushi, Derek, Jade, and Jesse.

I'll give another 30 minutes for any stragglers and then post the final here.

MESSAGE #74. Sat Dec 19 8:25:23 2009. Prof. Doug Hamilton wrote:

Rules for the take home final:

1. I'll post the final online for you right here at around 10:30 today.

2. Once you look at it, you have four hours, and you cannot use any outside sources (including friends). After four hours (or earlier if you wish - it shouldn't take much more than two) stop all work on the exam.

3. You can take it anytime on Saturday or Sunday.

4. Send it back to me as soon as possible (fax preferred 301-314-9067, or scan+email, or in an envelope postmarked by Monday).

FAQ

Can I use Saturday as a study day and take the exam on Sunday? Absolutely! :)

Can I look at the exam and then change my mind about taking it? No.

MESSAGE #73. Fri Dec 18 20:29:52 2009. Prof. Doug Hamilton wrote:

So far I've got 4 of you taking the take-home exam and 2 of you opting out!

MESSAGE #72. Fri Dec 18 15:50:41 2009. Prof. Doug Hamilton wrote:

Hi Class,

So I've got a plan now. Its not perfect, but satisfies these priorities:

1. The weather should help students 2. You should have a choice 3. You should have a real grade by Tuesday.

So here's the plan:

1. You can choose not to take the exam. In this case, for most of you, your final grade will be within a +/- step of where you are now. I will assign you a final exam grade based on how you did on the midterm and homework assignments.

2. You can choose to take the exam as a Take-Home Exam. You can do it any contiguous 4-hour block of time on Saturday or Sunday. You are on your honor not to talk to others and not to use your notes, books, the web, or other outside sources. Just you, the final, a pencil and blank sheets of paper! This will replace the grade that I would otherwise assign to you.

3. You can take it as a two-hour in-class exam in my office if you start by 5pm today! :)

WHAT YOU NEED TO DO:

- Option 1 is the default.

- If you want option 3, you need to show up at my office anytime before 5 today.

- And if you'd like option 2, you need to let me know by email by 10:30am tomorrow morning. I'll send you the exam by email and you'll need to get it back to me as soon as possible (either by scanning and email, fax to (301) 314-9067, or in the regular mail postmarked by Monday).

WHAT I WILL DO:

- I will assign you a grade by Tuesday and will adjust it later, if necessary.

- I will expect a lot more from you on the take home exam than I will on the in-class exam (e.g. you'll need a lot more points to make the same grade).

MESSAGE #71. Fri Dec 18 11:57:01 2009. Tilden Barnes wrote:

From an email sent by the university:

"FINAL EXAMS: "Final exams scheduled for Saturday, December 19, are canceled. Arrangements for make-up exams will be up to the discretion of the faculty. Should the faculty decide to reschedule, the Registrar's Office will make available the same schedule and locations on SATURDAY, JANUARY 30, 2010. Faculty members are asked to communicate with their students as soon as possible today to confirm the arrangements for their class's final exams and resolve any issues caused by this change. Faculty members will receive further instruction very soon.

"Final grades still need to be submitted by 2:00 p.m., December 22. This includes the grade of “I” (Incomplete) for those classes holding make-up final exams in January."

What does this mean for us???

@ Erin - I have a PDF scanned version of the mid-term solutions if you want them. Email me at tbarnesiv@gmail.com

--Tilden

MESSAGE #70. Fri Dec 18 11:53:35 2009. Erin Grand wrote:

FINAL EXAMS ARE CANCELLED FOR SATURDAY! It's official. We'll just have to wait for Dr. Hamilton to let us know what to do with this information.

MESSAGE #69. Fri Dec 18 11:35:40 2009. Erin Grand wrote:

Heather,

I was just wondering the same thing! Winter commencement just got cancelled/postponed so I am wondering what they are planning to do about exams and busses. I'd rather not walk to my first exam, through the snow, at 7 am.

Erin

Ps. Are the midterm and midterm solutions online somewhere and I just can't find them, or are they not up?

MESSAGE #68. Fri Dec 18 10:05:29 2009. Heather Weir wrote:

Happy Friday All!

Could someone give me an idea of what the procedure will be if we get a lot of snow tonight into tomorrow with respect to our final on Saturday?

Good luck to you all on your finals!

Thank you in advance.

MESSAGE #67. Thu Dec 17 12:49:03 2009. Jeremy Eaton wrote:

http://www.sphere.com/science/article/scientists-spot-nearby-super-earth-planet/19285097

I stumbled upon this article a bit earlier today. They found a big Earthlike planet 'probably with liquid water'. They also say it's quite hot -- perhaps this beast is analogous to Venus during the early stages of the runaway greenhouse effect? Pretty interesting.

Hope everyone had fun ice skating and I'll see everyone Saturday for the FINAL! *cue ominous music*

MESSAGE #66. Sun Dec 13 12:00:41 2009. Prof. Doug Hamilton wrote:

If you are coming to Ice the Prof! on Wednesday, there will be at least one car leaving from the CSS building at 12:15! I have room for 3 passengers in my car - if you can take some people in your car, please let me know!

Also, if you are interested, I am giving two talks on "Saturn's Largest Ring" next week:


• Goddard Extrasolar Planets Seminar (Dec. 17 @ 11:30am)
• Maryland Open House (Dec. 20 @ 8:00pm)
  

MESSAGE #65. Wed Dec 9 21:59:47 2009. Prof. Doug Hamilton wrote:

Sorry! I had to change "Ice the Prof" to next Wednsday! I forgot about a talk that I am scheduled to give at Goddard Thursday early afternoon. Ooops!

MESSAGE #64. Tue Dec 8 18:19:03 2009. Prof. Doug Hamilton wrote:

Ice the Prof! The ASTR430 Ice Skating event, also known as "extended office hours" to prep for Saturday's final.

Time: Wednesday, Dec. 16 12:30-3:30pm.
Place: Herbert Wells Ice Rink (5211 Paint Branch Parkway)
Cost: $5 to get in $2 to rent skates.
Directions: Leave campus from the main entrance, cross Rt. 1, pass the CP metro parking garage on the right, Wells Ice Rink is a few tenths of a mile further on the right.

You can walk from campus, or take a bus, or drive. Hope to see you all there! Oh .. and anyone who "Ices the Prof" (use the skates to cover him in shaved ice) more than the Prof ices you get bonus points on the final exam! :)

MESSAGE #63. Tue Dec 8 12:49:48 2009. Prof. Doug Hamilton wrote:

Today's class is moved to CSS0201 due to a power outage in our regular classroom. See you there @ 3:30pm.

MESSAGE #62. Sun Dec 6 22:11:28 2009. Erin Grand wrote:

I will be in the library, with Kate and probably Tony and Josh starting at about 5 pm. (I won't be there till 5:30, but that doesn't matter.) We can steal Dr. Hamilton and force him to give us answers. Muwhahaha! Or at least, just ask him for help.

Also, number 2 is giving me a slight headache just looking at it. Did anyone get anywhere?

MESSAGE #61. Sun Dec 6 20:18:00 2009. Lauren Woolsey wrote:

To Ryan: Yes, there should be Saturn masses as the unit, Professor Hamilton mentioned that to someone at the problem session on Thursday.

Speaking of problem sessions, are we having another one tomorrow (Monday)? I certainly hope so.

MESSAGE #60. Sun Dec 6 18:13:35 2009. Ryan Abrahams wrote:

I had a question from HW 7, number 1, part (c).

It quotes the mass of the ring as 6.5 * 10^(-8). Is this in units of Saturnian masses? Since it is too low to be in SI units, and Saturn is the only other interesting object in the system.

MESSAGE #59. Sun Dec 6 18:11:35 2009. Ryan Abrahams wrote:

MESSAGE #58. Wed Dec 2 21:48:53 2009. Michael Kelly wrote:

This may be overly simplistic, but it seems to me that if the sheet has infinite extent, then it can be treated as a circle rather than as a ring, since whatever area was in the 'hole' of the ring should be negligible. That said, I am still struggling with this problem.

MESSAGE #57. Wed Dec 2 15:23:43 2009. Tilden Barnes wrote:

For HW07 #1a, are we solving for a flat ring of radius R to infinity or a flat disk of infinite area (radius 0 to infinity)?

MESSAGE #56. Tue Nov 24 12:41:27 2009. Michael Kelly wrote:

Cool APOD of ice venting on Enceladus today:

http://antwrp.gsfc.nasa.gov/apod/astropix.html

APOD

MESSAGE #55. Fri Nov 20 20:13:32 2009. Prof. Doug Hamilton wrote:

We'll do a HW #6 review session Monday at 5pm in the ASTR Library (Room 1255).

Ring guys like me think this is pretty cool: What if Earth Had a Ring like Saturn? It's got a rockin' soundtrack too!

MESSAGE #54. Thu Nov 12 10:08:14 2009. Jade Williams wrote:

On HW#5 1e- I've come up with super super small values- I'm thinking way too small. I solved it graphically...but anyone get a rho(mantle) on the order of 10^-19 g/cm^3...?

MESSAGE #53. Wed Nov 11 11:23:26 2009. Prof. Doug Hamilton wrote:

Review Session tonight 5:00pm until late in the Astronomy Library Rm 1255!

MESSAGE #52. Tue Nov 10 21:57:31 2009. Jade Williams wrote:

Regarding the HW#5 session tomorrow, if anyone can stay, I'll be coming thru after 6pm- I'd love you to join me! Also, for problem 1c & 1d, how do we go about placing constraints on the moment of inertia equation that we derive? Is there an actual variable to be solved for...?

MESSAGE #51. Fri Nov 6 9:28:44 2009. Prof. Doug Hamilton wrote:

Hi Class,

I wanted to give you some more details about research opportunities in the Astronomy Department. These opportunities depend on you taking the initiative, but I'd like to offer to help you find the opportunity that is right for you! Here are the main possibilities.

• Senior Honors Project (for credit and departmental honors). Can start early! :)
• Independent Study Course (for credit) - freedom to choose your topic!
• Hourly position - $$, but you need to be more useful to your employer

Many astronomy professors will lead independent study course in their areas of research. Some have funded hourly positions for specific topics. Come talk to me, Grace Deming, or a professor who's research really interests you!

DH

MESSAGE #50. Sat Oct 31 17:04:03 2009. Tilden Barnes wrote:

Are the solutions for Homework #4 going to be posted in the Assignments or Handouts section?

MESSAGE #49. Wed Oct 28 19:52:08 2009. Daniel Hemmer wrote:

*edit to last post* and when i say e decreasing i obviously mean e is increasing. opposite wednesdays :)

MESSAGE #48. Wed Oct 28 19:44:29 2009. William Barnett wrote:

Lauren - Dan and I have been working on 3c for awhile as well and have come up with two solutions. We also decided to try conservation of angular momentum, however, when we finally got an equation that was a function of the moon's final distance, it yielded two solutions (we graphed it in MATLAB and used a function to find the intercepts). One of them was smaller than the current distance and the other appeared to be about two times as big as the current distance. Try using MATLAB to graph your solution and maybe it'll yield better results for you. Good Luck!

MESSAGE #47. Wed Oct 28 19:11:23 2009. Daniel Hemmer wrote:

Hey Jeremy For number 1, I think it is clear that h decreases but I don't see a way to easily (undergraduate level) find a way to show how a decreases and how much e decreases. Therefore I am beginning to think we are just supposed to show qualitatively, hence the sketching and not drawing perfectly for part c).

MESSAGE #46. Wed Oct 28 17:19:33 2009. Jeremy Eaton wrote:

Hi!

I'm working on the homework now and thus far I've reasoned my way through Problem 1. However, I'm not quite sure that my answer is sufficient. Are we supposed to show quantitatively (equations and such) how the orbit changes or simply use qualitative physical arguments.

If it's the former, could someone possibly give me a jump start on the situation?

Thanks!

MESSAGE #45. Wed Oct 28 17:02:20 2009. Lauren Woolsey wrote:

For problem 3c, I keep getting answers that don't make sense physically. My final distance from Earth to the Moon is smaller than the current distance.

Can anyone help me out with a starting point? I used conservation of angular momentum and the math looks right, but it just doesn't give a good result. Thanks.

MESSAGE #44. Wed Oct 28 15:21:47 2009. Daniel Hemmer wrote:

Will, myself, and hopefully others will be in the astro lab around 6 pm tonight to work on the homework.

MESSAGE #43. Fri Oct 23 17:53:51 2009. James Keane wrote:

A friend of mine sent me this image that actually reminded me of a picture that Lauren posted on this blog... so I decided to share it here.

http://i.imgur.com/GoCGR.jpg

Looks like we've gotten a bit better at going to Mars.

MESSAGE #42. Wed Oct 21 10:18:28 2009. Prof. Doug Hamilton wrote:

If you go to the Astronomy Department homepage at http://www.astro.umd.edu/ you can see a list of the upcoming science talks in the department for the week. You are all invited to attend any of this - just pick out ones where the titles are of interest!

Jeremy definitely knows his rings!

MESSAGE #41. Tue Oct 20 17:16:29 2009. Jeremy Eaton wrote:

Hey everyone,

Here's the article about solar system ring I inquired about today in class. Take a gander -- it's pretty cool (even if it isn't as neat as the Phoebe Ring).

http://www.npr.org/templates/story/story.php?storyId=113914677&ps=cprs

Enjoy.

MESSAGE #40. Thu Oct 15 7:15:47 2009. Prof. Doug Hamilton wrote:

Yep - no readin' + writin': all 'rithmetic. Roughly 3 problems, hopefully easier than HW problems.

Some have asked about answers to the sample midterm. I don't have the answers with me in the airport in Iowa, so I have no resources - just like you on the midterm! I'm working these out now, real time! And I have no paper ...

For 1), the answer is r=a(1-e²), heading outward, or f= 90^o. f is the true anomaly. This makes sense as the answer must be part way between pericenter and apocenter since the radial velocity is zero at those points.

For 3a), the answer with the correct dimensions is GM²/R⁴ (I dropped the "E" subscript for simplicity). Pressure is energy per unit volume, GM²/R is an energy, and R³ is a volume. Now the numbers: GM*M = 2*10³⁹ and R⁴ = 1.3*10²⁷. So pressure is 10¹² SI units or about 10⁷ bars. 10 million atmospheres does not seem too crazy!

For 3b), the dimensionless quantity is r/R, and the answer from a) should be multiplied by f(r/R), where f is an arbitrary function.

Good Luck today!

MESSAGE #39. Wed Oct 14 21:59:01 2009. Daniel Hemmer wrote:

Shushanta,

I do believe you are correct. In the directions on the practice he says, "There will not be a descriptive question this year," so I'm taking that as nothing like question 2.

MESSAGE #38. Wed Oct 14 20:21:54 2009. Shushanta Paudel Sharma wrote:

Hi. I know Dr. Hamilton told us in class about this but I'm a bit confused now :).

On the sample exam, there is a question about reading from the book, but he said we won't be having any conceptual questions right?... by conceptual I mean "not problem solving"...so we won't have any questions like #2 on the sample exam?

Thanks in advance!!!

Good Luck everyone. ^_^

MESSAGE #37. Tue Oct 13 13:45:21 2009. Prof. Doug Hamilton wrote:

ASTR430 in the news!

Here is a quote from the CMPS newsletter:

"Valerie Klavans (Undergraduate Astronomy Major) is this year's winner of the Nancy and Ira Shapiro Excellence in Undergraduate Research Award, the College Park Scholars top research award. Klavans worked with Paul Romani, a College Park Scholar Instructor and NASA-Goddard scientist, on the atmosphere of Titan, Saturn's largest moon, which has a nitrogen atmosphere as dense as our own."

Congrats Val!

Here is another one:

"Erin Grand (Astronomy Undergraduate Student) and Stefan Immler (Astronomy) were quoted on FoxNews.com in an article on NASA's Swift satellite acquiring the highest-resolution ultraviolet image of M31, a spiral galaxy in the constellation Andromeda. Grand was tasked with assembling 85 gigabytes of images from 300 observations. The image was selected as the Astronomy Picture of the Day for September 17. The story was also picked up by Science Daily."

Congrats Erin!

And finally:

"Doug Hamilton (Astronomy) with Anne Verbisher and Mike Skrutskie (U. Virginia) has discovered an immense dark dusty ring around Saturn. The new ring is a few hundred times larger than Saturn's main ring and, if visible to the naked eye, would be larger than the full Moon as seen from Earth. Ring material is painting the bright icy satellite Iapetus black on one side."

Here is the Astronomy Picture of the Day for Oct. 13 to go with it!

MESSAGE #36. Tue Oct 13 7:53:22 2009. Tilden Barnes wrote:

Thank you Lauren for the scan. I never got it, but I guess it was handed out the one day that I missed class. --Tilden

MESSAGE #35. Tue Oct 13 0:13:48 2009. Erin Grand wrote:

Also, was the question ever answered if the "difference for a planet" in 2a is asking what would change is the gas packet around the stars equator's was a planet or if the star was a planet?

I assumed the latter, but I am just making sure.

MESSAGE #34. Mon Oct 12 23:29:53 2009. Erin Grand wrote:

Hey guys!

I know I was bothering Doctor Hamilton about this a lot, but I have little idea of where to begin for question 3e. I plotted a few n's with values of C, h, and A that seemed to make sense. I know that there can only be a max of two answers, since nothing more than that makes sense physically, I'm just having trouble proving it mathematically. Any ideas?

Thanks!

MESSAGE #33. Mon Oct 12 22:12:07 2009. Lauren Woolsey wrote:

Tilden, didn't you get a copy of the homework in class?

Here's a scanned picture: (http://www.languages.umd.edu/lh/germancluster/Pics/astrhw4orbit.png)

MESSAGE #32. Mon Oct 12 20:58:36 2009. Tilden Barnes wrote:

That is very scary. I used Firefox to read the PDF file and I also downloaded the file and opened it using the latest version of Adobe Acrobat Reader and it is still blank. Does anyone have any suggestions?

MESSAGE #31. Mon Oct 12 18:02:27 2009. Richard O'Steen wrote:

Tilden: That big blank space should contain five graphs of the parameters of the orbit. You are supposed to interpret the graphs in order to draw the orbit at a few different times.

-Ricky

MESSAGE #30. Mon Oct 12 14:45:39 2009. Tilden Barnes wrote:

For HW3 #1, it says to "sketch the following orbit", but I don't see any orbit we are asked to sketch. Are we just supposed to sketch an arbitrary orbit? I see a large space on the HW sheet between #1 and #2 but it is blank. Is there a reason for this?

MESSAGE #29. Mon Oct 12 7:09:48 2009. Prof. Doug Hamilton wrote:

Hi Class,

Take a look at the sample midterm on the ASTR430 assignments page. Since we have seven quizzes on the reading, the midterm will be all problem solving. It will be closed book. We have been doing lots of orbit problems, so you will want to memorize at least the five equations at the top of the conics handout. You'll want to know how to do energy and angular momentum problems, dimensional analysis, and how to quickly test your answers using units, limits, symmetries, etc.

I've also posted HW#4 which has some more orbit problems. It is not due until the end of October, but starting on it would be a good test of your problem solving skills. More details in class on Tuesday ...

DH

MESSAGE #28. Sun Oct 11 23:13:16 2009. James Keane wrote:

So, according to the lecture schedule, we have a midterm this Thursday over Chapters 1-13 (excluding 4), Homeworks 1-3, Quizzes 1-3.

Seeing as how I have four other midterms this week (I know, insane), I was wondering if you could elaborate what the format of the exam would be, so I could start studying as soon as possible. Do you tend to focus on the homework/lecture material more, or the reading/discussion material, or is it a balance between the two? Will we need to memorize particular formulas?

Thanks in advance!

MESSAGE #27. Sun Oct 11 8:40:22 2009. Lauren Woolsey wrote:

Thank you for the help, Professor!

Someone just sent this picture to me, and I think it is absolutely fantastic. It shows all the planetary missions of the past fifty years. It's too big to post here, but the link should work just fine.

MESSAGE #26. Sat Oct 10 8:51:43 2009. Prof. Doug Hamilton wrote:

Hi Lauren and the rest of you!

#2: Think about how the problem would differ for a basketball.

#3" "radial turning point" - these are just the minimum and maximum radial distances that the orbit achieves. At those locations, the orbit "turns" from inward to outward motion or vice versa.

Take a look back at HW#2 where you did a problem with C, the energy per unit mass (specific energy).

If anyone is interested in a HW#3 problem solving session, come to the library Monday 5-6pm. Otherwise, I'll see you all Tuesday!

MESSAGE #25. Thu Oct 8 18:47:57 2009. Lauren Woolsey wrote:

Hey guys, hopefully people have started looking at the homework due on Tuesday.

For #2, isn't the centrifugal force F = mv^2/r? If so, why would this be different for a planet?

For #3, I don't know how to find an equation for specific energy C, was this covered in class? Also, what exactly does a "radial turning point" mean?

Thanks in advance! Lauren

MESSAGE #24. Thu Oct 8 9:10:03 2009. Prof. Doug Hamilton wrote:

Hi Class!

Type "Phoebe Ring" into Google and see what comes up! Our announcement of a new ring around Saturn got a lot of good press yesterday! I tell you more about it next week ...

Be nice to the next sub! :)

MESSAGE #23. Mon Oct 5 21:57:38 2009. Daniel Hemmer wrote:

also for #3, it's asking for the circular velocity so you know it is following a circular orbit once it reaches 1 AU. since it is going around in a circle it is fairly straight forward to calculate the velocity. (by balancing the two forces that are keeping it there).

MESSAGE #22. Mon Oct 5 20:56:16 2009. Michael Kelly wrote:

The homework solutions give an example (#3C) in words, "... the packet of gas will follow a Keplerian orbit. Since there is only a radial force and the gas starts from rest, this orbit will be a straight line trajectory to the origin (i.e. an ellipse with e=1)." So if I understand this problem right, I'd say you were on the right track.

MESSAGE #21. Mon Oct 5 16:46:42 2009. Heather Weir wrote:

I could use a little direction/help with #3. I originally started to find v using: Gm1m2/r^2 = v^2/r, but realized that we are coming from infinity to 1 AU. Any pointers would be greatly appreciated. I think I understand the second part, by setting kinetic energy = thermal energy.

Thank you for your help. Heather

MESSAGE #20. Sun Oct 4 19:40:55 2009. Michael Kelly wrote:

Jeremy, sorry to take so long to respond to your question on #1. I used angular momentum to get v^2. You end up with an expression that can be substituted for v^2. I'm not sure why you're seeing (1 - e^2) in the denominator, but it might help factoring it to (1 - e)(1 + e).

MESSAGE #19. Sun Oct 4 19:37:19 2009. Lauren Woolsey wrote:

Jeremy, sorry I didn't see your post before now! As long as you take r at pericenter and you're /really/ careful with your algebra, it should work out. Also, instead of trying to find v, just plug in v^2 = h^2/r^2.

MESSAGE #18. Fri Oct 2 17:29:02 2009. Jeremy Eaton wrote:

Jade,

The minimum and maximum speeds of the orbit occur at the farthest distance and closest approach to the central mass respectively. When you enter your formula on the Planet Calculator, you should plug in the corresponding position for 'r' in terms of the eccentricity and semimajor axis (based on the ellipse geometry). In other words, you will need to use the calculator twice, once for R at pericenter and again for the apocenter.

MESSAGE #17. Fri Oct 2 15:31:34 2009. Jade Williams wrote:

For problem 1 has anyone yet used the solar system calculator? I've done so, and v-knot is listed for each of the planets. How do we determine max & min velocities though?

MESSAGE #16. Wed Sep 30 20:36:38 2009. Jeremy Eaton wrote:

Hi! I've read your hints for Problem 1 and I'm still a bit perplexed. I was able to derive the result without any direct reference to the angular momentum; instead substituting the corresponding formulae for r and v into the energy equation. When I try to make reference to the angular momentum, I end up with a similar result (-GM/2a) but with an extra factor of (1-e^2) in the denominator. Can anyone provide more insight on how to use the angular momentum equation?

MESSAGE #15. Wed Sep 30 20:19:09 2009. Lauren Woolsey wrote:

Ricky: You should know where the parent satellite is right after the two separate, and so find an equation with that radius, a, and e. Solve for a so you can plug it in to find e (which you then plug back into the side equation you just created).

MESSAGE #14. Wed Sep 30 20:15:39 2009. Lauren Woolsey wrote:

MESSAGE #13. Wed Sep 30 19:19:19 2009. Richard O'Steen wrote:

Hi all,

I ended up not being able to make it to the problem session today and have a question about number two. Considering angular momentum gets me down to how the quantity a(1-e^2) will change, but not how to determine the changes in a and e individually. It seems like e and a should both increase. Does anyone have an idea on how to get the two separately? I was thinking that we might also have to use conservation of orbital energy since it is mentioned in the problem.

Thanks, Ricky

MESSAGE #12. Tue Sep 29 17:59:48 2009. Prof. Doug Hamilton wrote:

Homework #2 is now due on Tuesday Oct. 6!
And there will be a problem session at 5:15pm Wednesday Sept. 30 in the Astronomy Library (CSS 1255). If you can't make it, send a friend from the class!

MESSAGE #11. Mon Sep 28 21:05:05 2009. Michael Kelly wrote:

Thanks Lauren! I was off in the weeds there ...

MESSAGE #10. Mon Sep 28 14:27:47 2009. Lauren Woolsey wrote:

Michael: Thank you so much! Everything fell right into place one I had a platform from which to jump.

As for the velocity of the 1 ton satellite...to launch it out, the velocities will have to be different, right? (e.g. two figure skaters on frictionless ice, where one weight nine times the other....the small skater will go shooting off when they push off each other, but the bigger one will move somewhat, too) I'm not too sure of it, since I'm still not sure where to start, but it just seems like they wouldn't have the same velocity at release.

MESSAGE #9. Sun Sep 27 22:37:27 2009. Michael Kelly wrote:

A couple of things that helped me get started on the first problem were the distance equation from the conic section handout, the distance equation derived in class 9/17 which is the same equation as in the conic section handout but for r(theta) instead of r(t), and the h = r*v*sin(theta) expression for angular momentum. Choose a place on the ellipse where h = rv, then start substituting expressions into the energy equation. Also helpful to remember that you can get v^2 by using h^2 = r^2 * v^2.

I'm looking at the second one and wondering what the velocity of the 1 ton satellite would be at release. Since at that point the spring would be fully extended and shouldn't be imparting any v in the z direction, v would have to be the same as the 9 ton satellite, right?

MESSAGE #8. Sun Sep 27 16:42:46 2009. Lauren Woolsey wrote:

Has anyone started the homework yet? For some reason, I can't seem to get any good footing with it. Is there an equation I should start with, or something in the notes that would lead me in the right direction? I don't know why it seems so unapproachable.

MESSAGE #7. Thu Sep 24 20:05:00 2009. Prof. Doug Hamilton wrote:

Iceland: Rift Valley at Thingivir
<-- America              Europe -->

MESSAGE #6. Mon Sep 21 10:31:29 2009. Prof. Doug Hamilton wrote:

The meeting room that I was thinking about is taken, so we'll use the library in CSS1255. See you at 12!

MESSAGE #5. Sat Sep 19 22:30:32 2009. Prof. Doug Hamilton wrote:

Remember the problems solving session Monday 12-1pm in the conference room across from my office CSS1245. Bring questions!

For problem #2, use the "Orbital Integrations" link ...

MESSAGE #4. Fri Sep 18 15:58:38 2009. Heather Weir wrote:

There is a talk at Goddard's Visitor Center on Sept. 24th on Jupiter. Check out: Virtual Trip to Jupiter for more details and to save a spot.

There will be 2 presentations and showings of "Largest" on Science on a Sphere at 7 and 8 pm..

MESSAGE #3. Thu Sep 17 17:56:19 2009. Prof. Doug Hamilton wrote:

Here's the UV Andromeda picture from ASTR430 researcher Erin Grand!
Erin's Summer Research

MESSAGE #2. Thu Sep 17 17:23:02 2009. Lauren Woolsey wrote:

Hey everyone! Thought I'd mention a (somewhat-)pertinent current event: COROT-7b.

There are already tons of news stories about it, so you only need google the name, but here are a few articles: ESA, Times Online (UK), and even a wikipedia page.

Artist conception of this super-hot, Earth-mass (5 Earth Masses, but you know how it is...) exoplanet:

MESSAGE #1. Mon Sep 14 18:25:35 2009. Prof. Doug Hamilton wrote:

Welcome to the ASTR430 Blog! I hope that you find it useful. It works best if you all make an effort to post cool stuff here for the rest of the class to enjoy. You can use Simple HTML Commands to include links and images. I will consider your blog usage as part of your participation grade, so please use it wisely!

Here is the full color version of the figure from my exoplanet paper - looks pretty toasty!

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