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### Re: Astronomy C

Posted: March 22nd, 2010, 1:10 pm
What resources did u guys use at state? If at all possible, could u guys send me the resources?

thanks,
celtics09

### Re: Astronomy C

Posted: March 22nd, 2010, 1:49 pm
Also, there was a multiple choice question about our local group and the choices were that its:

A) An irregular group within a supercluster
B) A regular group within a supercluster
C) An irregular group not in a supercluster
D) A regular group not in a supercluster

OR something to that effect

I know that we are in a supercluster (Virgo Supercluster), but I don't know if our group is irregular or regular... Anyone know out there?
Well, it's shaped like a dog bone or a dumbbell. My guess, that would count as irregular.

What did you think of the test overall?
I thought it was a very good test... I focus on DSO's/Galaxy/THings of that nature, while my partner focuses on Math/Physics, and I thought the questions were pretty easy. I did like the graphing and charting we had to do though, although I had to double check my "HR" graph cause of the logarithmic scale My partner said a few math questions were weird..

Overall, good test, good questions.

### Re: Astronomy C

Posted: March 22nd, 2010, 6:16 pm
The rules say we may have to analyze light curves... can anyone give me an example of that would look like, and what kind of questions would go along with it?

### Re: Astronomy C

Posted: March 22nd, 2010, 7:32 pm
The rules say we may have to analyze light curves... can anyone give me an example of that would look like, and what kind of questions would go along with it?
I would think one question would be to ID what kind of variable star a certain light curve is for. Also, I've seen a question asking about the light curve of Epsilon Aurigae at every competition I've been at so far (Invitationals, Regionals, and States). they gave the picture of the light curve and asked which object it is (Epsilon Aurigae)

### Re: Astronomy C

Posted: March 25th, 2010, 12:15 pm
The spectral lines of two stars in a particular eclipsing binary system shift back and forth with a period of 8.00 months. The lines of both stars shift by equal amounts, and the amount of the Doppler shift indicates that each star has an orbital speed of 9.00×10^4. What are the masses of the two stars? Assume that each of the two stars traces a circular orbit around their center of mass.

How would you solve this?

### Re: Astronomy C

Posted: March 25th, 2010, 10:23 pm
The spectral lines of two stars in a particular eclipsing binary system shift back and forth with a period of 8.00 months. The lines of both stars shift by equal amounts, and the amount of the Doppler shift indicates that each star has an orbital speed of 9.00×10^4. What are the masses of the two stars? Assume that each of the two stars traces a circular orbit around their center of mass.

How would you solve this?
Just use Kepler's Third Law.
m1+m2=t^2/a^3.
They give you the period in the first part (3/4 years), and with the period and the speed, you can find out the distance the stars travel (d=vt). Once you know that they are orbiting in circles, you can see that the distance in the circumference, and use that to find out the average separation of the stars. Now you have both t and a. By the fact that both stars are going the same speed, you can tell that they are the same mass, so you have all of the parts of the equation. Just make sure that your units are in years, solar masses, and AU.

### Re: Astronomy C

Posted: March 28th, 2010, 10:55 am
Had States competition... and didn't know a thing about Supernovae, so therefore, I failed at the first 3 pages. Out of 5. But still scraped a 5th place, saved by downloading a lot of wikipedia pages onto my computer

My partner conveniently broke his hand the day before

### Re: Astronomy C

Posted: March 28th, 2010, 10:58 am
Had States competition... and didn't know a thing about Supernovae, so therefore, I failed at the first 3 pages. Out of 5. But still scraped a 5th place, saved by downloading a lot of wikipedia pages onto my computer

My partner conveniently broke his hand the day before

### Re: Astronomy C

Posted: April 7th, 2010, 2:44 pm
I've been having a bit of trouble trying to find a value of Hubble's constant to use for equations since all of the values I've found are estimates.
Would I be better off just asking the proctor what value they used before the test?
Also, how would one use the constant to determine the age of the universe (in years)?

### Re: Astronomy C

Posted: April 7th, 2010, 5:21 pm
I've been having a bit of trouble trying to find a value of Hubble's constant to use for equations since all of the values I've found are estimates.
Would I be better off just asking the proctor what value they used before the test?
Also, how would one use the constant to determine the age of the universe (in years)?
The value of 65 km/s/mpc is most commonly used (as the Hubble constant). However, values may differ between 50 and 80 km/s/mpc depending on the proctor, so it is best to ask for clarification before the test. As for the age of the universe, if you know hubble's law stating: v = H * d, you can rewrite it so that 1/H = d/v. d/v is equivalent to t (time), so you would go from there and convert as needed to years.

### Re: Astronomy C

Posted: April 9th, 2010, 6:15 pm
I've been having a bit of trouble trying to find a value of Hubble's constant to use for equations since all of the values I've found are estimates.
Would I be better off just asking the proctor what value they used before the test?
Also, how would one use the constant to determine the age of the universe (in years)?
Like the person above me wrote, the most accurate value is estimated to be 65 km/s/mpc. The test however will give you the value of hubble's constant in the question or on a reference sheet if you need it. And the value they give you is often not 65 km/s/mpc. If you are sure you are not given a value, make sure you need it to answer the problem, and then ask the proctor.

### Re: Astronomy C

Posted: April 10th, 2010, 3:23 pm
Everyone better vote in the poll: What is your favorite celestial object?

### Re: Astronomy C

Posted: April 24th, 2010, 6:30 pm
I have a question for you guys regarding binders.
According to my friend who does this event, you're allowed a laptop with files on it or any size binder. He has this absolutely massive binder that I argue Is actually counter-productive since it takes so long to look through--even with various post it markings. I say to him, couldn't you just have a laptop and use cntrl-F to find things. Thoughts?

### Re: Astronomy C

Posted: April 24th, 2010, 6:37 pm
I use a small binder of important equations and some info on each DSO. There is no point swamping a binder with piles of information that will almost certainly not come up.

If you want a huge data reservoir, I would guess that a laptop would be your best bet.

Hope that helps.

### Re: Astronomy C

Posted: April 25th, 2010, 9:06 am
I have a question for you guys regarding binders.
According to my friend who does this event, you're allowed a laptop with files on it or any size binder. He has this absolutely massive binder that I argue Is actually counter-productive since it takes so long to look through--even with various post it markings. I say to him, couldn't you just have a laptop and use cntrl-F to find things. Thoughts?
This friend, you say, has the right idea. Making such a large binder not only helps you attain lots of information about the subject, but also helps you learn the information through the process of making the binder. I do the same thing and even though the ctrl F on the laptop may seem easier, some of the questions people have to find on the laptop people with the binder would already know without even having to search through the thing.