## Astronomy C

Smithy0013
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### Re: Astrology C

nomynameisnotkevin wrote:
Smithy0013 wrote:I can't seem to find a mathematical relationship between period and luminosity. Is it necessary just to use graphs and estimate the point on the x and y axis? Or is there an actual equation floating around there somewhere? I derived one myself using a couple known Cepheids but I'd much rather use one from the science community.

I ran into the statement that Period is directly related to luminosity as well, but have no idea if there's a specific equation for everything. Maybe just for certain types. Also, kinda curious what you got for those Cepheids.

Well I only used classical cepheids since its different for every type. But soon after posting this i finally found a relationship (on wikipedia of course I wouldnt look there....). So I compared them for a few and my equation was pretty close so I just deleted it unfortunately. It was the same basic constract with a coefficiant multiplied by a log (I used a natural log as opposed to the base 10 on wikipedia) subtracted by another constant. It really wasnt that impressive since all i did was plug values in excel and make a trend line. Anyway, on wikipedia there is the equation (-2.43)(LOG(P)-1)-4.05 equals your absolute magnitude. Then either use distance modulus or convert to luminosity (another thing I had difficulty finding) and use inverse square law.

JCicc
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### Re: Astronomy C

Watch the test exchange for this year's PA State exam and the SE PA Regional exam. They should be up shortly. Feedback as always is appreciated. I'm going to need a ruling on this year's clever meme, as well. I will admit that "coruscate" is a bit obscure, but "trifling stellar remnant of luminosity class VII" should have easily translated as "little star," silly people.

syo_astro
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### Re: Astronomy C

JCicc wrote:Watch the test exchange for this year's PA State exam and the SE PA Regional exam. They should be up shortly. Feedback as always is appreciated. I'm going to need a ruling on this year's clever meme, as well. I will admit that "coruscate" is a bit obscure, but "trifling stellar remnant of luminosity class VII" should have easily translated as "little star," silly people.

I think I must've found your meme (yay google), and I can already say I'm gonna like this test .
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Kyaanon
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### Re: Astronomy C

There was a question I ran into that didn't quite make sense to my partner or I. The question went something like this: "You locate a visual binary in the night sky that is too far for the distance to be determined with parallax. How do you determine the distance?"

No other details were provided, which game my partner and I a bit of a headache :/
Do you have to assume other things in order to solve it? It was an essay question
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zyzzyva980
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### Re: Astronomy C

In this case, it looks like you'd just describe the method you would use to determine the distance if you weren't able to use parallax. You wouldn't actually need to determine the numerical distance.
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syo_astro
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### Re: Astronomy C

Kyaanon wrote:There was a question I ran into that didn't quite make sense to my partner or I. The question went something like this: "You locate a visual binary in the night sky that is too far for the distance to be determined with parallax. How do you determine the distance?"

No other details were provided, which game my partner and I a bit of a headache :/
Do you have to assume other things in order to solve it? It was an essay question

Ughhhh I hate essay questions...they're not good for the test taker or the grader >.> (well, I guess that depends on the person). I would imagine there's a few ways to do this? I would very much ask the grader if you can. I think you kind of have to make some observations here to actually get it. Of course, you have to make it under the constraints given (that is it's a visual binary and decently far away). Unfortunately or fortunately you could use a lot of ways to figure this out then? I question also whether I should assume that they meant trigonometric parallax, spectroscopic parallax...I'll try to use a method without just in case.

You could find the angular size of the system by observation. Using spectroscopy you could maybe derive a velocity graph. You could also find the temperature of each star and probably the luminosity of each star dependinggggg on the system. You could maybe use some sort of mass-luminosity relation and then find the mass of each star (I know I'm being cheap there, but they do exist and you just need to figure out the spectral class and luminosity class of the objects...if it can't be applied I could list other ways of doing this, whatever). With that, you can find the mass of the system, then I would hope you can find the period of orbit either by observation or from your velocity graph. With period and mass you can find the physical semi-major axis. With that and the observed angular size of the system, you can then use the small-angle formula to I believe get the distance to the system.

Phew, hope that helped!
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Kyaanon
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### Re: Astronomy C

Thanks bunches! It definitely sounds more legitimate than my solution Mine involved waiting several billion years for one of the stars to become a white dwarf and then waiting a bit longer for it to go type 1a supernova, assuming everything ends up going my way.
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syo_astro
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### Re: Astronomy C

Kyaanon wrote:Thanks bunches! It definitely sounds more legitimate than my solution Mine involved waiting several billion years for one of the stars to become a white dwarf and then waiting a bit longer for it to go type 1a supernova, assuming everything ends up going my way.

Haha, yeah a lot of this depends on how you approach the question...creative still XD. But considering there's lots of work to be done, I think you kinda wanna get your answer now .
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hipparcos
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### Re: Astronomy C

Kyaanon wrote:There was a question I ran into that didn't quite make sense to my partner or I. The question went something like this: "You locate a visual binary in the night sky that is too far for the distance to be determined with parallax. How do you determine the distance?"

No other details were provided, which game my partner and I a bit of a headache :/
Do you have to assume other things in order to solve it? It was an essay question

Hm... they might be looking for "dynamical parallax": http://en.wikipedia.org/wiki/Dynamical_parallax.
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syo_astro
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### Re: Astronomy C

hipparcos wrote:
Kyaanon wrote:There was a question I ran into that didn't quite make sense to my partner or I. The question went something like this: "You locate a visual binary in the night sky that is too far for the distance to be determined with parallax. How do you determine the distance?"

No other details were provided, which game my partner and I a bit of a headache :/
Do you have to assume other things in order to solve it? It was an essay question

Hm... they might be looking for "dynamical parallax": http://en.wikipedia.org/wiki/Dynamical_parallax.

Funny, doesn't that look familiar . Either way Kyaanon, I assume you're going to nats (because I know things...like hey, hipparcos I may have talked to you before, heh), so I don't think there will be essay questions. Either way, better study up! Nationals certainly won't have an easy astro test.
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### Re: Astronomy C

The 2014 Nationals Exam is up: http://www.aavso.org/science-olympiad-2014.

I hope everyone enjoyed it!
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syo_astro
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### Re: Astronomy C

HEY PEOPLE. The user above me (Tad!) has told me a hint that I can post here for the topic next year!!!!! Excitement aside, the hint is along the lines of this. The topic will be "Stellar Evolution and __", people shouldn't bother studying RR Lyrae, Cepheids, and guess I could list other things but that's the gist. Basically it's not 100% variable stars, but variable stars still can play a role. I'd personally study them (including RR Lyrae and Cepheids, why not) for fun anyway...but beside the point. Good luck, I hope everyone enjoys the summer and remember to move onward to the edge . Also, I hope some of the tests I'm making pop up somewhere, hope whoever gets those enjoys. Right now all I'm doing is making a test for SSSS on It's About Time, but I'll get back to astro eventually.
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Unome
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### Re: Astronomy C

syo_astro wrote:
Kyaanon wrote:There was a question I ran into that didn't quite make sense to my partner or I. The question went something like this: "You locate a visual binary in the night sky that is too far for the distance to be determined with parallax. How do you determine the distance?"

No other details were provided, which game my partner and I a bit of a headache :/
Do you have to assume other things in order to solve it? It was an essay question

Ughhhh I hate essay questions...they're not good for the test taker or the grader >.> (well, I guess that depends on the person). I would imagine there's a few ways to do this? I would very much ask the grader if you can. I think you kind of have to make some observations here to actually get it. Of course, you have to make it under the constraints given (that is it's a visual binary and decently far away). Unfortunately or fortunately you could use a lot of ways to figure this out then? I question also whether I should assume that they meant trigonometric parallax, spectroscopic parallax...I'll try to use a method without just in case.

You could find the angular size of the system by observation. Using spectroscopy you could maybe derive a velocity graph. You could also find the temperature of each star and probably the luminosity of each star dependinggggg on the system. You could maybe use some sort of mass-luminosity relation and then find the mass of each star (I know I'm being cheap there, but they do exist and you just need to figure out the spectral class and luminosity class of the objects...if it can't be applied I could list other ways of doing this, whatever). With that, you can find the mass of the system, then I would hope you can find the period of orbit either by observation or from your velocity graph. With period and mass you can find the physical semi-major axis. With that and the observed angular size of the system, you can then use the small-angle formula to I believe get the distance to the system.

Phew, hope that helped!