## Astronomy C

pjgscioisamazing
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### Re: Astronomy C

astro124 wrote:
Schrodingerscat wrote:
Smithy0013 wrote:So why use B-V index to find temperature of a star when you can use Wien's law? What is the point of B-V index besides finding Temp?
For one, from an observational standpoint, one can measure B-V index with just two magnitude measurements with a B and a V filter, as opposed to needing a full spectrometer to use Wien's law. Otherwise, it is just another way to measure temperature/color of a star to my knowledge.
Isn't Wien's law more common to use (at least on Scioly tests)? On my state test a few weeks ago I remember seeing two maximum wavelength to temperature problems but zero B-V color index questions. That being said, you'll regularly see B-V color on the X-axis of H-R diagrams.
Wien's Law is more common on Scio tests as it is a simple relation that is easy to understand and use. B-V and temperature relations are much more complicated, depending on terms of B-V to different powers with differing coefficients that are affected by things such as metallicity and the life stage of a star.

Wien's Law is for blackbodies, and stars are only approximated as black bodies. Wien's Law gives the temperature of a blackbody that would emit the same total amount of light as the star, called the effective temperature.

Also, as said above, in observational astronomy you will be working with magnitudes of stars in some sort of filter system, commonly UBVRI. A common goal, especially in studies of star clusters, is to generate an H-R Diagram to determine things like the age and distance of the cluster. It is easiest to use the B-V value as a temperature indicator. This is why most H-R Diagrams of star clusters will be Color-Magnitude Diagrams (ie. V magnitude versus B-V Index).
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Smithy0013
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### Re: Astronomy C

So where is the best reliable source for info on DSOs? Like for distance im getting a lot of variance (for example, wikipedia says Mira is 300 ly away and this wiki says 420). Id rather not get points off from a strict test proctor because i have a 20 percent error

astro124
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### Re: Astronomy C

Smithy0013 wrote:So where is the best reliable source for info on DSOs? Like for distance im getting a lot of variance (for example, wikipedia says Mira is 300 ly away and this wiki says 420). Id rather not get points off from a strict test proctor because i have a 20 percent error
If you can you should use the Chandra X-ray Observatory Website. This is the most reliable for DSO info, but unfortunately not all DSOs are listed there. However, for a good majority of the list I would spend some time looking around at different websites (wiki, NASA, Chandra, university websites, etc., academic papers, etc.). As with anything in astro you might get similar but not exact info from these different sources. The test proctor should understand.

Mira (Chandra): http://chandra.harvard.edu/photo/2005/mira
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darkwinters
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### Re: Astronomy C

I remember something came up on last year's state test about observing elliptical motion when the orbital plane was tilted with respect to us.

I don't remember much of that question at this point, but has anyone come across something similar?

BipolarEconomist
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### Re: Astronomy C

Do you guys recommend memorizing DSOs?
I know that a lot of our competition this year is going to be centered around the DSOs, but I'm bringing a laptop and binder with the SciOly wiki's charts with the information on DSOs with me, so I think I should be OK.

Also, I noticed that a lot of questions this year ask you about declination, flux, density, distance, etc. of DSOs. Some info. is on Wikipedia pages, some is not. Where do you guys find all the information? If you have any links, share pls? =D

Thanks!
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Smithy0013
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### Re: Astronomy C

BipolarEconomist wrote:Do you guys recommend memorizing DSOs?
I know that a lot of our competition this year is going to be centered around the DSOs, but I'm bringing a laptop and binder with the SciOly wiki's charts with the information on DSOs with me, so I think I should be OK.

Also, I noticed that a lot of questions this year ask you about declination, flux, density, distance, etc. of DSOs. Some info. is on Wikipedia pages, some is not. Where do you guys find all the information? If you have any links, share pls? =D

Thanks!
Yes I would memorize what each DSO basically looks like (It can make the difference on ID sections on a long test) but also keep a substantial photo library somewhere (I use MS OneNote for all my astro stuff). Don't use wikipedia. A lot of the info is decent but sometimes you find things that just arent right. Go to Chandra's website for information (shoutout to astro124 for recommending it to me so i can give it to you). Its an actual observatory so they tend to know what they're talking about. They will give you Right acenstion and declination, distance but not luminosity and density in most situaitons. Usually you can know that stuff from knowning what type of DSO it is and knowing the characteristics of it. The wiki chart's are a great first look quick info and I can answer probably 70 percent of DSO questions with it

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### Re: Astronomy C

Smithy0013 wrote:
BipolarEconomist wrote:Do you guys recommend memorizing DSOs?
I know that a lot of our competition this year is going to be centered around the DSOs, but I'm bringing a laptop and binder with the SciOly wiki's charts with the information on DSOs with me, so I think I should be OK.

Also, I noticed that a lot of questions this year ask you about declination, flux, density, distance, etc. of DSOs. Some info. is on Wikipedia pages, some is not. Where do you guys find all the information? If you have any links, share pls? =D

Thanks!
Yes I would memorize what each DSO basically looks like (It can make the difference on ID sections on a long test) but also keep a substantial photo library somewhere (I use MS OneNote for all my astro stuff). Don't use wikipedia. A lot of the info is decent but sometimes you find things that just arent right. Go to Chandra's website for information (shoutout to astro124 for recommending it to me so i can give it to you). Its an actual observatory so they tend to know what they're talking about. They will give you Right acenstion and declination, distance but not luminosity and density in most situaitons. Usually you can know that stuff from knowning what type of DSO it is and knowing the characteristics of it. The wiki chart's are a great first look quick info and I can answer probably 70 percent of DSO questions with it
Definitely memorize what each DSO looks like IN MULTIPLE WAVELENGTHS, as well as some basic information about it -- i.e. T Pyx is a recurrent nova of a white dwarf and low-mass main sequence star surrounded by shells of gas from previous detonations, and there was an exceedingly long wait between the two most recent outbursts with the last one being in 2011. Doing so will help you get through the DSO/ID section of a test that much faster. Hell, depending on how much you know and how easy the test is, you might even be able to get through the whole section without consulting your notes at all!

Wikipedia is actually a very good starting point for several DSOs, but yeah, some are obscure enough they don't have pages at all (mostly the ones that look like alphabet soup). Chandra is also good, as are any NASA/ESA press releases or any sites associated with a college/university or astronomical organization, such as AAVSO, and of course, APOD. Also advised are ANY observatories or space missions (Hubble, Spitzer, ROSAT, Fermi, to name a few). Basically, a good amount of information will come up on the first page or two of google search results for the DSO.

If you're really into astro, you can also read the research papers that come up, but going to that level isn't usually necessary for astro... unless you or your testwriter (or both) are insane :P

Edit: Of course, this is only a starting point. As you become more comfortable with the astro event and what's expected of you, you'll want to search more specifically and read more in-depth things, such as the aforementioned research papers, and perhaps an astrophysics textbook (the general consensus around here is that Carroll and Ostlie is very very good, though also rather dense and very heavy on the math).

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darkwinters
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### Re: Astronomy C

What would you reckon are the most likely math/orbital questions to come up on a state test?

Smithy0013
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### Re: Astrology C

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.

nomynameisnotkevin
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### Re: Astrology C

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.

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