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Astronomy C

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Re: Astronomy C

Posted: March 18th, 2019, 8:49 pm
by Name
SciolyHarsh wrote:On the golden gate test, how would you do 17 c, d, and f?
17a use keplers third law- 9.965 solar mass
17b mass times distance = mass times distance- 5.97 solar mass
17c You know the distance of star b is 20 au. Convert to km, multiply by 2pi (it's a circular orbit). The period is 112 years, convert to seconds, and divide the circumference of the circle by the period in seconds. I got 5.98 km/s
17d Same thing except distance is now 30 au. I got 8.41 km/s
17e. Use the mass-lumo-radius relationship for lumo in solar lumo. Convert to absolute magnitude, use distance modulus
17f. In 17e you find the distance to be 7.9389 parsecs. 50 au divided by 7.9389 = 6.3. For an explanation- distance is 7.9 parsec. Convert to au is 1637521 au. This can be the radius- convert this to a circumference, which is 10288848 au. divide 50 by this to get 4.86E-6. This is in degrees. Convert to arc sec by muliplying by 360, 60, and 60 to get 6.3. I'm not sure about the if the seperation is visable or not, that's probably just some random piece of trivia. (Wiki says yes if seperation > 1 arc sec for telescopes, less for professional telescopes, interferometry, or space-based equipment.)
Edit: added in explanations for other parts of the question as well
17. Star B and Star C orbit one another in a binary system with a separation of 50 AU. Assume
that the two stars have circular orbits. Star B has a radius that is twice that of the Sun and
an effective temperature of 3,500 K.
(a) The period of Star B’s orbit around their common barycenter is 112 years. What is the
combined mass of Star B and Star C, in Solar Masses?
(b) Star B lies 20 AU from the barycenter of the two orbits. What is the mass of Star B,
in Solar masses?
(c) What is the orbital velocity of Star B, in kilometers per second?
(d) What is the orbital velocity of Star C, in kilometers per second?
(e) The apparent magnitude of Star B is 5. How far away is this system, in parsecs?
(f) What is the maximum apparent separation of Star B and Star C, in arcseconds? Is this
separation visible to current telescopes (i.e., would this be a visual binary)?
I think this is right? I don't usually do the math stuff and im kinda rusty on astro math.

Re: Astronomy C

Posted: March 18th, 2019, 9:45 pm
by SciolyHarsh
Name wrote:
SciolyHarsh wrote:On the golden gate test, how would you do 17 c, d, and f?
17a use keplers third law- 9.965 solar mass
17b mass times distance = mass times distance- 5.97 solar mass
17c You know the distance of star b is 20 au. Convert to km, multiply by 2pi (it's a circular orbit). The period is 112 years, convert to seconds, and divide the circumference of the circle by the period in seconds. I got 5.98 km/s
17d Same thing except distance is now 30 au. I got 8.41 km/s
17e. Use the mass-lumo-radius relationship for lumo in solar lumo. Convert to absolute magnitude, use distance modulus
17f. In 17e you find the distance to be 7.9389 parsecs. 50 au divided by 7.9389 = 6.3. For an explanation- distance is 7.9 parsec. Convert to au is 1637521 au. This can be the radius- convert this to a circumference, which is 10288848 au. divide 50 by this to get 4.86E-6. This is in degrees. Convert to arc sec by muliplying by 360, 60, and 60 to get 6.3. I'm not sure about the if the seperation is visable or not, that's probably just some random piece of trivia. (Wiki says yes if seperation > 1 arc sec for telescopes, less for professional telescopes, interferometry, or space-based equipment.)
Edit: added in explanations for other parts of the question as well
17. Star B and Star C orbit one another in a binary system with a separation of 50 AU. Assume
that the two stars have circular orbits. Star B has a radius that is twice that of the Sun and
an effective temperature of 3,500 K.
(a) The period of Star B’s orbit around their common barycenter is 112 years. What is the
combined mass of Star B and Star C, in Solar Masses?
(b) Star B lies 20 AU from the barycenter of the two orbits. What is the mass of Star B,
in Solar masses?
(c) What is the orbital velocity of Star B, in kilometers per second?
(d) What is the orbital velocity of Star C, in kilometers per second?
(e) The apparent magnitude of Star B is 5. How far away is this system, in parsecs?
(f) What is the maximum apparent separation of Star B and Star C, in arcseconds? Is this
separation visible to current telescopes (i.e., would this be a visual binary)?
I think this is right? I don't usually do the math stuff and im kinda rusty on astro math.
Sorry i don't really understand what you did for 17f. But thanks for the rest

Re: Astronomy C

Posted: March 19th, 2019, 3:49 am
by Name
SciolyHarsh wrote:
Name wrote:
SciolyHarsh wrote:On the golden gate test, how would you do 17 c, d, and f?
17a use keplers third law- 9.965 solar mass
17b mass times distance = mass times distance- 5.97 solar mass
17c You know the distance of star b is 20 au. Convert to km, multiply by 2pi (it's a circular orbit). The period is 112 years, convert to seconds, and divide the circumference of the circle by the period in seconds. I got 5.98 km/s
17d Same thing except distance is now 30 au. I got 8.41 km/s
17e. Use the mass-lumo-radius relationship for lumo in solar lumo. Convert to absolute magnitude, use distance modulus
17f. In 17e you find the distance to be 7.9389 parsecs. 50 au divided by 7.9389 = 6.3. For an explanation- distance is 7.9 parsec. Convert to au is 1637521 au. This can be the radius- convert this to a circumference, which is 10288848 au. divide 50 by this to get 4.86E-6. This is in degrees. Convert to arc sec by muliplying by 360, 60, and 60 to get 6.3. I'm not sure about the if the seperation is visable or not, that's probably just some random piece of trivia. (Wiki says yes if seperation > 1 arc sec for telescopes, less for professional telescopes, interferometry, or space-based equipment.)
Edit: added in explanations for other parts of the question as well
17. Star B and Star C orbit one another in a binary system with a separation of 50 AU. Assume
that the two stars have circular orbits. Star B has a radius that is twice that of the Sun and
an effective temperature of 3,500 K.
(a) The period of Star B’s orbit around their common barycenter is 112 years. What is the
combined mass of Star B and Star C, in Solar Masses?
(b) Star B lies 20 AU from the barycenter of the two orbits. What is the mass of Star B,
in Solar masses?
(c) What is the orbital velocity of Star B, in kilometers per second?
(d) What is the orbital velocity of Star C, in kilometers per second?
(e) The apparent magnitude of Star B is 5. How far away is this system, in parsecs?
(f) What is the maximum apparent separation of Star B and Star C, in arcseconds? Is this
separation visible to current telescopes (i.e., would this be a visual binary)?
I think this is right? I don't usually do the math stuff and im kinda rusty on astro math.
Sorry i don't really understand what you did for 17f. But thanks for the rest
Basically apparent separation (arc sec)= separation in au/distance in parsecs. The other part was just how you can calculate it without knowing this equation.

Re: Astronomy C

Posted: March 19th, 2019, 7:59 am
by PM2017
Name wrote:
SciolyHarsh wrote:
Sorry i don't really understand what you did for 17f. But thanks for the rest
Basically apparent separation (arc sec)= separation in au/distance in parsecs. The other part was just how you can calculate it without knowing this equation.
For further explanation, here's why this is the case:

There's a thing called small angle approximation, that says that theta ~ tan(theta) for small angles, because as the angle gets smaller, sin theta is approximately the same as the arc length created by that angle, and cos theta approaches 1. (.: sin(theta) = theta; cos(theta) = 1). Since tan(theta) = sin(theta)/cos(theta), tan(theta) = theta/1.

Then, you know that you have a right triangle (assuming the object is face on), with the adjacent side being the distance to the object (let's call this "D"), and the opposite side being the diameter/length/whatnot of the object (let's call this "L" ). So, you get tan(theta) = L/D, and since we said earlier that tan(theta) = theta, you get your final equation as theta=L/D. Remember, of course, that this is in radians. You almost certainly have to convert to degrees, arcminutes, arcseconds, or milliarcseconds.

Since 1 rad = 206,625 arcseconds, you could just set your equation to theta = 206,625L/D. Make sure L and D are the same. I made the mistake of thinking that the 206625 was to convert from pc to AU (by definition, the conversion from AU to pc is the same as radians to arcseconds.), and that's why I had to make the edit below.

EDIT: I removed the other paragraph since it was wrong.

Re: Astronomy C

Posted: April 17th, 2019, 8:52 am
by Rossyspsce
getting thrown on this event for next year(2019-2020 season), because our astro people will all be graduating. What should I do to study for this event/where should I start?

Re: Astronomy C

Posted: April 17th, 2019, 10:06 pm
by PM2017
Rossyspsce wrote:getting thrown on this event for next year(2019-2020 season), because our astro people will all be graduating. What should I do to study for this event/where should I start?
I would get familiar with HR Diagrams, Stellar evolution, and binary stars to start with. I listed some of the necessary calculations in a post earlier in this thread (I might have shared the link with you already, I don't entirely recall). After you get familiar with stellar evolution, I would try learning about supernovae (in general, and then specifically about the individual types. Type Ia SN are super important.) After that, I would just reserach topics in general, take tests to see what topics get tested often, and repeat.

For DSOs, which you can't really do anything about until rules come out, I would first try to gather images and basic info from Wikipedia, Chandra, APOD, and other similar sources and make profiles for each DSO. Then, what we did was we went and read a bunch of abstracts from academic papers on each of the DSOs. (I'm convinced that this is what made us such a strong team for astro last year at state -- unfortunately, this year's test had a much, much smaller focus on DSOs :( It is what it is, I guess...).Really if you can ID images, and have some info to ctrl+f through, you should be able to get at least 70% of DSO questions no problem.

I can provide more specific advice if you have certain topics you need help with specifically, as can others on this forum, I'm sure.

Re: Astronomy C

Posted: April 17th, 2019, 11:50 pm
by Name
Rossyspsce wrote:getting thrown on this event for next year(2019-2020 season), because our astro people will all be graduating. What should I do to study for this event/where should I start?
Not sure if this is the best way but here's how I learned astro.

I started off with the math stuff- you don't really need new rules for that. There's a formula sheet on the wiki page, it's a good start, but make your own math sheet (as well as everything else). Take tests- they can even be old tests because math stuff doesn't change much, and make sure you understand the equations you do have, while finding more equations that are useful. Once you get a good basis of math and a little bit of practice, it becomes pretty easy to do, very rarely are there extremely obscure equations used, you should have all the information needed to solve any problem in your sheet. The only really hard thing I find about math is usually when some graph is involved (lol I literally can't read graphs).

Make your notes for the general knowledge stuff covered in the rules. I would dedicate at least a page of information to each specified topic they have in the rules, and research them in depth, and out anything relevant or interesting in your notes. I find that I don't use these notes very much in competition, but the background knowledge gained from doing this is extremely valuable. Understanding concepts of astro allows you to quickly answer questions, while if you don't understand the concept you waste time trying to find it in your notes, with the possibility it might not even be in your notes. It also allows you to make a educated guess for questions you may be unsure of.

Finally, the DSOs. Because my partner usually takes the math portion, these notes are by far my most used in competition (once I almost exclusively just used this document alone at one comp) so you wanna make these good. Make detailed notes for each, include as many pictures as you can. Make sure you can ID them basically to 100% accuracy. As a general guideline for researching these, I entire first page of google results after searching the DSOs and sift through those. I also compiled the websites together by saving them as a PDF and combining them, which is useful if you finish the test early and you're missing one very specific detail about a DSO or something. (I also did this for some general topics, tbh it's not that useful unless the writer just copied everything from wikipedia). I never found the need to study for DSOs specifically (I personally feel reading papers and such is a bit overkill), the priority should be just understanding and digging deeper into the general concepts, which carries over into your understanding of DSOs.

Take a few practice tests to see what your missing, and improve on that. Also practice tests are extremely useful for the math portion, although not as much so for everything else.

Re: Astronomy C

Posted: April 19th, 2019, 4:02 pm
by OrigamiPlanet
This problem set from this particular PA finals is really confusing me, problems 80-83. Could someone help me understand what formula or formulas I need to be using for this?

Test link:
https://scioly.org/wiki/images/7/73/Pen ... stions.pdf

Key link:
https://scioly.org/wiki/images/1/12/Ans ... states.pdf

Thanks!

Re: Astronomy C

Posted: April 21st, 2019, 6:27 pm
by flembo17
Rossyspsce wrote:getting thrown on this event for next year(2019-2020 season), because our astro people will all be graduating. What should I do to study for this event/where should I start?
I do the DSOs and concepts sections. For DSOs, be sure to start working on collecting information once they get released, especially if your school goes to invitationals early in the year as it can take a good chunk of time even if split between you and your partner. Be sure to go through wikipedia, NASA, Chandra, research papers, etc for each one. It is very crucial to have as much information as possible for each one because the DSO sections can range from very basic to very in depth. My partner and I find it helpful to keep all the DSO notes we take on one document, and I would definitely recommend that. Definitely be able to identify all of them with ease. I would also suggest keeping a separate document just for every picture you can find of each DSO (different wavelengths, their constellations, etc) and add to it as you take practice tests.

For the concepts, don't be afraid to start from the very basics- it is best to work yourself up. Start with HR diagram and stellar evolution and make sure to know it very well. Skipping to more complex topics without having a strong foundation can really hurt you on tests that are heavier on the conceptual stuff. A big part of stellar evolution is to be able to locate regions and pathways on the HR diagram and to be able to explain the life of different mass stars in detail. Once you are solid on these topics, begin to explore the more niche stuff and take tests to find information you are weaker on. Also, don't be afraid to download a million wikipedia documents. Although a wikipedia document will never be able to replace you knowing something solid from hours of studying, it can be very helpful on occasion.

I don't do math but just know most tests go beyond the equations and formulas on the rules. Take old math sections and build your own formula document. One thing to watch out for on the math is units- those can get tricky.

Re: Astronomy C

Posted: April 21st, 2019, 7:03 pm
by syo_astro
flembo17 wrote: For the concepts, don't be afraid to start from the very basics- it is best to work yourself up. Start with HR diagram and stellar evolution and make sure to know it very well. Skipping to more complex topics without having a strong foundation can really hurt you ...
All fair advice (though, see earlier for Name's opinion on papers too I guess). I'll add that HR diagrams and stellar evo. aren't even only basics. There's a lot of complicated bits you can stumble upon while reading. Even ignoring that, stellar evolution contains a tremendous amount of material. Lots of people lose plenty of points on these questions too. The main thing is to not get intimidated and to ask questions!

I think learning style can vary some, and I personally liked to move between lots of topics and get a rough view on things with examples. Then I'd come back and refine this knowledge. That way I would get good at mixing my DSO ID / info. studies with my stellar evo. studies (and it was fun pretty pictures then!). Obviously harder to do without the upcoming DSOs, but you can just use past ones to get the same idea. Probably everyone agrees, though, that the basic "tools" of astronomy like HR diagrams, imaging, and spectra, are essential to master regardless of the year's focus.
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