Astronomy C

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Re: Astronomy C

Post by Ashernoel » March 21st, 2017, 10:16 am

antoine_ego wrote:I wonder what the Nationals test will be like. Is it just me or is this topic a lot easier than last year in terms of math?
Yea that's what my partner the math guy told me too. So that's fun :D
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Re: Astronomy C

Post by syo_astro » March 21st, 2017, 10:43 am

Technically this is a science competition, so the math is never supposed to be particularly hard ;). At the same time, algebra, units, and graph reading surprisingly or not does result in many mistakes, so...
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Re: Astronomy C

Post by Avogadro » March 21st, 2017, 5:44 pm

syo_astro wrote:Technically this is a science competition, so the math is never supposed to be particularly hard ;). At the same time, algebra, units, and graph reading surprisingly or not does result in many mistakes, so...
Science = math

Or at least when literally every event you do has a lot of math, at least. I guess I might be speaking from a bit of a biased standpoint.

So once one has exhausted the first page of Google for every concept and object, what would you all recommend going towards? Any textbook recommendations?
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Re: Astronomy C

Post by syo_astro » March 21st, 2017, 7:06 pm

I am staunchly opposed to the idea that science = math. But then I am also biased, just in the opposite direction :P. I just figure when you can have a class mostly about observations and concepts that logically come from those observations, science isn't just math...of course I'm not saying math is unrelated to science, but science is certainly not *purely* math (as your equals sign might imply :P).

The 1st page of google for every *concept*? The concepts sometimes can have quite a bit of depth depending on what search terms you use! In fact, varying up search terms and looking at the first 3 - 5 links sometimes gets you more than just a basic search. One specific tip is you can look at research papers if you're looking for new concepts or ways of looking at objects (it takes practice, but mainly just read the abstract/intro/conclusion).
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Re: Astronomy C

Post by Unome » March 29th, 2017, 2:57 pm

Question: why do higher-mass stars have the radiative layer outside the convective layer while low(er) mass stars are the opposite?
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Re: Astronomy C

Post by Adi1008 » March 29th, 2017, 3:18 pm

Unome wrote:Question: why do higher-mass stars have the radiative layer outside the convective layer while low(er) mass stars are the opposite?
Greater mass means greater pressures and temperatures at the center of the star, creating a large temperature gradient between the core and the outer layers - this results in convection. Furthermore, the outer layers have a very low density, so energy flows through them more efficiently by radiation
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Re: Astronomy C

Post by Unome » March 30th, 2017, 8:47 am

Adi1008 wrote:
Unome wrote:Question: why do higher-mass stars have the radiative layer outside the convective layer while low(er) mass stars are the opposite?
Greater mass means greater pressures and temperatures at the center of the star, creating a large temperature gradient between the core and the outer layers - this results in convection. Furthermore, the outer layers have a very low density, so energy flows through them more efficiently by radiation
Ok; so do larger stars also contain an inner radiative section? (and why does this section exist in lower-mass stars)

Also, unrelated; does anyone know anything about the concept of the lifetime of an atomic transition? Apparently it's related to the spectral line width, but I can't really understand most of the documents that talk about it (too much math).
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Re: Astronomy C

Post by Magikarpmaster629 » April 3rd, 2017, 6:08 am

So I already talked about this with East and Lumosityfan on IRC earlier and got a good answer, but I'll ask it again because I think it's really interesting:

In a typical CO white dwarf, a type Ia supernova will occur after carbon burning begins due to the runoff nuclear reaction that follows it. But from what I found (Carrol and Ostlie's Introduction to Modern Astrophysics) carbon burning begins at 1.3 solar masses. The "vanilla" explanation (as someone on stackexchange put it) for the type Ia supernova is that it occurs after the Chandrasekhar limit is reached; the value of which is 1.4 solar masses. Comparing these, I suspected that this was a misconception- the type Ia supernova is (at least somewhat) unrelated to the Chandrasekhar limit, and does not need to reach it to explode, although white dwarfs cannot surpass that limit (except in special cases). East and Lumosityfan seemed to confirm this, and the white dwarf does not need to hit the limit; anyone else have input on this?
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Re: Astronomy C

Post by Unome » April 3rd, 2017, 6:41 am

Magikarpmaster629 wrote:So I already talked about this with East and Lumosityfan on IRC earlier and got a good answer, but I'll ask it again because I think it's really interesting:

In a typical CO white dwarf, a type Ia supernova will occur after carbon burning begins due to the runoff nuclear reaction that follows it. But from what I found (Carrol and Ostlie's Introduction to Modern Astrophysics) carbon burning begins at 1.3 solar masses. The "vanilla" explanation (as someone on stackexchange put it) for the type Ia supernova is that it occurs after the Chandrasekhar limit is reached; the value of which is 1.4 solar masses. Comparing these, I suspected that this was a misconception- the type Ia supernova is (at least somewhat) unrelated to the Chandrasekhar limit, and does not need to reach it to explode, although white dwarfs cannot surpass that limit (except in special cases). East and Lumosityfan seemed to confirm this, and the white dwarf does not need to hit the limit; anyone else have input on this?
I've also heard that the values were different and unrelated (though I tend to stick with 1.4 for most tests since that's what usually gets the points).
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Re: Astronomy C

Post by jonboyage » April 3rd, 2017, 7:32 am

Unome wrote:
Magikarpmaster629 wrote:So I already talked about this with East and Lumosityfan on IRC earlier and got a good answer, but I'll ask it again because I think it's really interesting:

In a typical CO white dwarf, a type Ia supernova will occur after carbon burning begins due to the runoff nuclear reaction that follows it. But from what I found (Carrol and Ostlie's Introduction to Modern Astrophysics) carbon burning begins at 1.3 solar masses. The "vanilla" explanation (as someone on stackexchange put it) for the type Ia supernova is that it occurs after the Chandrasekhar limit is reached; the value of which is 1.4 solar masses. Comparing these, I suspected that this was a misconception- the type Ia supernova is (at least somewhat) unrelated to the Chandrasekhar limit, and does not need to reach it to explode, although white dwarfs cannot surpass that limit (except in special cases). East and Lumosityfan seemed to confirm this, and the white dwarf does not need to hit the limit; anyone else have input on this?
I've also heard that the values were different and unrelated (though I tend to stick with 1.4 for most tests since that's what usually gets the points).
I wonder if the rotation of the object has anything to do with it? When a star is rotating rapidly, its centrifugal pseudo-force would have an effect on the pressure on the core, increasing the total mass that the white dwarf can accommodate. The conventional mass of 1.4 I believe is for non-rotating objects.

As for the 1.3, can you explain how fusion makes the white dwarf unstable? In my head, I imagine that fusion would have the effect of decreasing the "load" on the degenerate matter and help prevent collapse.
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