## Astronomy C

EastStroudsburg13
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### Re: Astronomy C

TheBalticSea wrote:Anyway! I saw there was a question about calculating distance based on recessional velocity (I think? maybe i remembered incorrectly).
If the typical wavelength of an object's spectrum is n and it's shifted so that the "new" wavelength is m , you calculate (n-m)/n and then multiply that by the speed of light to get the recessional velocity. From there, you use Hubble's recessional velocity-distance relation to get:
d = v/H
where d is distance (assuming you're using parsecs for distance and m/s for recessional velocity), v is, well, velocity, and H (usually denoted H sub naught) is Hubble's constant (most recently valued at around 70.4).
Just an added tidbit, the equation (n-m)/n that Baltic mentioned is also the equation for redshift (z). That would mean that recessional velocity is the speed of light times the redshift (or (c)(z)). Just thought that that might be useful.
wyu1229 wrote:Can anyone tell me how to do these two calculations?

A binary star produces the light curve and the radial velocity diagram shown below. Star A has a temperature of 17700 K and a radius of 5RSUN, while star B has a temperature of 11000 K and a radius of 1.5RSUN. The primary eclipse occurs every 3.85 days. The separation of the stars is 1.5E10 m. The extrema on the radial velocity graph are 250 km/s and -190 km/s for one curve; for the other, they are 93 km/s and -33 km/s. Use this information for numbers 39 – 52. (taken from 2007 PA exam).

1) Calculate the orbital velocity of Star A
2) Calculate the orbital velocity of Star B

2) 63 km/sec

If you want a link to the actual test, here it is: http://www.tufts.edu/as/wright_center/p ... C_exam.pdf
I'm thinking that since that test is focused on variable stars, you shouldn't have to calculate something like that on a test. However, I can't help you with the calculations, so sorry about that. The good news is that it's unlikely to be found on a test, and not many other teams will be able to solve that either.
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crazy77
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### Re: Astronomy C

I'm kind of confused about what's fair game for a test because i have an invitationals test from last year (the topic was relatively the same right?) and it had a good amount of stuff on stars. Along that line of thought, has anyone here taken an astronomy test for NY states? If so what was it like?

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### Re: Astronomy C

dreaminghigh wrote:
smartkid222 wrote:
koumbare wrote:Will we have to know parallax?
yes
Why do we have to know parallax? Isn't this year's topic galaxies?
Not sure how good my answer is, but I'll try to explain.

Parallax is used in calculating distance. This year's topic is galaxies, but there are a lot of other things you can be tested on, since astronomy is so broad in itself. Variable stars are definitely still on the test, and on my regional test, we had to calculate distances to them (and other things) more than once. Knowing parallax isn't quite enough, either. On my test, all the distance answers had to be in light years, but the equations usually just had parsecs in them. You need to be able to convert to AU and then to light years if necessary.

It's really just a basic tool used in astronomy, and from my experience, you always have to know the basics. For example, one of the tie-breakers on my test was, "What is the equation for the force of gravity?"

crazy77, I haven't taken a NY state test, but a lot of things are fair game in this event. Just try to make sure you touch on everything, especially identifications. If you don't have pictures in your resources, try to reason things out if you get IDs. My brother and I use laptops, and during our test, half of the images wouldn't show up, but we still figured out the answers using reasoning. Make sure you know the Deep Sky Objects, especially Epsilon Aurigae.

Hope that helps!

dreaminghigh
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### Re: Astronomy C

Not sure how good my answer is, but I'll try to explain.

Parallax is used in calculating distance. This year's topic is galaxies, but there are a lot of other things you can be tested on, since astronomy is so broad in itself. Variable stars are definitely still on the test, and on my regional test, we had to calculate distances to them (and other things) more than once. Knowing parallax isn't quite enough, either. On my test, all the distance answers had to be in light years, but the equations usually just had parsecs in them. You need to be able to convert to AU and then to light years if necessary.

It's really just a basic tool used in astronomy, and from my experience, you always have to know the basics. For example, one of the tie-breakers on my test was, "What is the equation for the force of gravity?"

crazy77, I haven't taken a NY state test, but a lot of things are fair game in this event. Just try to make sure you touch on everything, especially identifications. If you don't have pictures in your resources, try to reason things out if you get IDs. My brother and I use laptops, and during our test, half of the images wouldn't show up, but we still figured out the answers using reasoning. Make sure you know the Deep Sky Objects, especially Epsilon Aurigae.

Hope that helps!

Ahh, thank you. Thank you. That kind of helps, but my head is going to hurt now with all the extra cramming I'm about to do.
Astronomy - 1st
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crazy77
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### Re: Astronomy C

crazy77, I haven't taken a NY state test, but a lot of things are fair game in this event. Just try to make sure you touch on everything, especially identifications. If you don't have pictures in your resources, try to reason things out if you get IDs. My brother and I use laptops, and during our test, half of the images wouldn't show up, but we still figured out the answers using reasoning. Make sure you know the Deep Sky Objects, especially Epsilon Aurigae.

Hope that helps!

I can't really find any good pictures for epsilon aurigae though. And you know how typically the images that show up on google are the colorized ones where things aren't really the color that they are in the picture but they add the color to kind of make it easier to see things? Will they ever use that on a test or only the plain, black and white images? It can be pretty hard to identify a lot of these things without the color.

dreaminghigh
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### Re: Astronomy C

crazy77 wrote:
crazy77, I haven't taken a NY state test, but a lot of things are fair game in this event. Just try to make sure you touch on everything, especially identifications. If you don't have pictures in your resources, try to reason things out if you get IDs. My brother and I use laptops, and during our test, half of the images wouldn't show up, but we still figured out the answers using reasoning. Make sure you know the Deep Sky Objects, especially Epsilon Aurigae.

Hope that helps!

I can't really find any good pictures for epsilon aurigae though. And you know how typically the images that show up on google are the colorized ones where things aren't really the color that they are in the picture but they add the color to kind of make it easier to see things? Will they ever use that on a test or only the plain, black and white images? It can be pretty hard to identify a lot of these things without the color.
I'm thinking that the people wouldn't use black and white images because they are hard to distinguish. And for the test, the images vary as they could show the colored ones or have the normal colored ones. I would suggesr that instead of using google images, that you just look through the links of what google came up with to find some more pictures. Or go to Epsilon Aurigae's wikipedia page and go to the bottom for the links and click them and see if they come up with any more pictures.
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FullMetalMaple
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### Re: Astronomy C

I can't really find any good pictures for epsilon aurigae though. And you know how typically the images that show up on google are the colorized ones where things aren't really the color that they are in the picture but they add the color to kind of make it easier to see things? Will they ever use that on a test or only the plain, black and white images? It can be pretty hard to identify a lot of these things without the color.
That's because there really aren't any. Truthfully, I don't think I've ever seen an ID for Epsilon Aurigae, if that makes you feel any better. I've seen black and white images only once before, but they're usually in color. I think the images I have in my notes are from Google images (my brother actually found all the images we have in our notes), and it's usually fairly easy to identify things with just those images. Now that I think about it, NASA's image gallery is an excellent source. I just looked at it, and all the images on my regional test were from there.
Ahh, thank you. Thank you. That kind of helps, but my head is going to hurt now with all the extra cramming I'm about to do.
You're very welcome! Ha, I wouldn't worry much about it beyond knowing distance equations and how great of a distance you can determine with parallax. Are you competing soon? If so, good luck!

crazy77
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### Re: Astronomy C

FullMetalMaple wrote:
I can't really find any good pictures for epsilon aurigae though. And you know how typically the images that show up on google are the colorized ones where things aren't really the color that they are in the picture but they add the color to kind of make it easier to see things? Will they ever use that on a test or only the plain, black and white images? It can be pretty hard to identify a lot of these things without the color.
That's because there really aren't any. Truthfully, I don't think I've ever seen an ID for Epsilon Aurigae, if that makes you feel any better. I've seen black and white images only once before, but they're usually in color. I think the images I have in my notes are from Google images (my brother actually found all the images we have in our notes), and it's usually fairly easy to identify things with just those images. Now that I think about it, NASA's image gallery is an excellent source. I just looked at it, and all the images on my regional test were from there.
Ahh, thank you. Thank you. That kind of helps, but my head is going to hurt now with all the extra cramming I'm about to do.
You're very welcome! Ha, I wouldn't worry much about it beyond knowing distance equations and how great of a distance you can determine with parallax. Are you competing soon? If so, good luck!

So, just as an example, if you had to ID the bullet cluster they might give this picture: ??? or more like this ???? (these are both from NASA) I'm just asking because on the only test I've taken for astronomy the pictures were black and white. There wasn't a whole lot of IDing to do anyway but still

FullMetalMaple
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### Re: Astronomy C

That first image of the bullet cluster is the exact image I had on my test. I've seen the second before, too. I wish I would have thought of looking at NASA images earlier - this is actually going to help me a lot in the future, too, lol.

smartkid222
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### Re: Astronomy C

They can give you any image of a DSO. Last year at regionals and states the pictures were in color. This year at regionals they were black and white. There are many pictures of epsilon aurigue.
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