## Astronomy C

syo_astro
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### Re: Astronomy C

Looked at that Northview test on the wiki for astro. I noticed that there is a mistake in the answer key. The first question should be Antares, not Arcturus...unless I just really haven't been studying. Guess I'll just move on...
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astro124
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### Re: Astronomy C

I know this may be a bad question to ask considering that I have state in a month, but how hard are the Physics and Math formulas/equations going to be? This is my first year doing Astro C (I placed 3rd in Reach for the Stars last year though) and I'm getting stressed at to what Math/Physics concepts I should be putting my study time into (I understand parallax and spectroscopic parallax). Is there anything that is a must to study in terms of the Laws and equations?

Also, if it helps I'm in the Arizona competition (which supposedly isn't half as competitive as New York or Pennsylvania).

Any help is appreciated.

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### Re: Astronomy C

The important equations you're going to need mainly deal with distance or intrinsic properties. So, definitely parallax and distance modulus, Kepler's Laws, Wien's Displacement Law, Hubble's Law, and the Stefan-Boltzmann Law. The Astronomy Wiki has some information about math, and also has a sample formula sheet at the bottom with the links. Also, you should probably be familiar with relationships that relate to stellar evolution and this year's topic, like Schwarzchild radius and perhaps the Jeans mass. In general, there's always something more you can know: that's the blessing and the curse of Astro. But the ones that are a necessity are the ones I mentioned in the second sentence.

Good luck! Since you're just starting, expect the first competition to be a learning experience, but then as you compete more, by the time you reach your senior year you should be pretty good.
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### Re: Astronomy C

Since the topics for this year specifically include Cepheids and XRB systems, I would also definitely learn the Period-Luminosity Relationship (we had a discussion earlier in the thread on what the right P-L equation was) and math for binary systems, which does include Kepler's Laws as EAST stated above, but also general physics stuff like circular velocity and orbital period.
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syo_astro
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### Re: Astronomy C

For a third input just for fun. I'd also think that for math there'd be plenty of graphing questions. What I mean by this is basically all sorts of questions can be asked about the light curves of variable stars (*cough* cepheids *cough*). You know, recently I've been exploring the possibility of neutron star math...I feel like there is some, but I'm not fully sure whether it would be asked about. I've also been seeing tons of black hole math which scares me. Though, I pretty much agree with east on this one.
I also try to put all my formulas into a section of my binder, and then just constantly practice them or look at the concepts. I found deriving the distance modulus a few times to actually help a lot in figuring out how it works. Also, know what B-V index is...it's quite simple XD. The other part of astro math is to know how to convert between units. Aside from that binary stars have a few different questions that can be asked based on the type. There are also some various standard candle facts to know, and some things about spectra and whatnot as the rules states. Aside from that if you want more practice on random math you can always look on the test exchange. Guess I'll go back to banging my head over what I need for states in about a month...but summary is: the math is doable, just practice, and most of all good luck and have fun!
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astro124
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### Re: Astronomy C

Thanks for the all the help guys. I've already started chipping away at some of the equations but first I need to finish my DSO research (trying to get as much info as I can).

However I do have one more question. How are you able to determine the distance to an object just by knowing the length of an image of it in parsecs (example on the Northview 2013 Test)? Also can you use the arcseconds of a DSO's image to calculate the length of the object in parsecs or LY?
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AlphaTauri
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### Re: Astronomy C

Uhh, there are two questions on Northview that both kind of deal with finding distance from angular measurements...

If you mean 1c, that one uses the parallax formula: $D=\frac { 1 }{ p" }$, where D is distance in parsecs and p" is the parallax angle in arcseconds.

Therefore, $D=\frac { 1 }{ 5.89\quad *\quad { 10 }^{ -3 }\quad arcsec } =170.\quad pc$

If you mean 2b, this one involves the small-angle formula, $\frac { angular\quad diameter\quad (arcsec) }{ 206265" } =\frac { linear\quad diameter }{ distance }$.

We can guesstimate that V838 is about 70" across from the image. To get its linear diameter, we approximate that it has been expanding for 2.89E7 seconds - from this - and then multiply that by the speed of light, 3E8 m/s, since this is a light echo and the only thing "moving" is light. This gets us a radius of 8.67E15 m, which we'd then multiply by 2 to get the diameter. (I'm not being very precise here, since the key also makes some pretty significant approximations, notably in the expansion time.)

Therefore, $\frac { 70" }{ 206265" } =\frac { 2(8.67*{ 10 }^{ 15 }m) }{ distance }$

And we solve for distance, which turns out to be 5.11E19 m.
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BigD47
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### Re: Astronomy C

Does anyone know any good resource books for Astronomy?

syo_astro
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### Re: Astronomy C

BigD47 wrote:Does anyone know any good resource books for Astronomy?
I believe we've said some already. There are tons of good college websites online, and we've also said that an amazing textbook for the event is An Introduction to Modern Astrophyiscs by Carrol and Ostlie. There may be some other books, but quite a few things for the event can be found online, and some textbooks in fact aren't necessarily any better for what you need (information for the DSOs, for example, is generally supposed to come from online reaserch). If you looked throughout this thread you'd be able to see many of the major sites posted. Are you just more adamant for reading? I guess I could try to look some up, but ask. Hope that helps, good luck!
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astro124
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### Re: Astronomy C

AlphaTauri,

Why did you say for problem 2b, it was 70 arcseconds instead 90 arcseconds (the image says 90). Also, wouldn't there be an easier way of just using LY or parsecs to put your answer in (I'm not talking about converting once you get your solution at the very end, but rather converting at the very beginning).

Also, for the problem 2d , do you know why the instructor squared the radius and temperature?

Finally, how do use Cepheids to calculate distance.
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