Astronomy C

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astroblue
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Re: Astronomy C

Post by astroblue » January 16th, 2013, 4:57 pm

Ohhhhh, gotcha! Thank you very much!

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Re: Astronomy C

Post by SimplyNeedLogic » January 16th, 2013, 11:01 pm

This may sound like a very stupid question, but how do you ID DSO's? Like based on the color/shape? Because pictures can be taken at different angles using X-Ray, Optical, Infared, and Radio telescopes. Thanks so much in advance. c:

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Re: Astronomy C

Post by EastStroudsburg13 » January 17th, 2013, 7:57 am

Well, the pictures can't exactly be taken at different angles, since we're at a fixed point in the sky. Changes in the telescope's location due to Earth's orbit around the Sun aren't going to have much bearing on the perspective at which we'll see DSO's. So shape is definitely a big one. They will also give images that will be taken at different wavelengths, so you have to be prepared for that. This is what will make certain pictures look different than others, because a relatively dark area in infrared might be brighter in X-ray.

Assuming you don't have an array of very strong space telescopes at different wavelengths home, you just have to search for as many images from as many wavelengths as possible. You may not hit every single wavelength, but remember that most test supervisors are going to be finding images the same way you are, so frequently they'll use the most common image, which is usually taken by a major satellite like Chandra.

Of course, images are only one way they can have you identify DSO's. They can use light curves, H-R Diagrams, you name it. Astronomy is incredibly broad, so you have to be prepared for everything they could possibly throw at you.
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Re: Astronomy C

Post by Orange714 » January 24th, 2013, 11:54 am

If they asked you to identify a DSOs based on a light curve or a spectra is there any way to identify it, without having like a picture of it? Like what we've been doing is just finding the spectra/light curve then matching it up...But I'm interested in learning how to identify without having a picture present...is that possible? For some of the DSOs I can't find the light curves/spectra. Kinda rambling sorry XD
Thanks in advance

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Re: Astronomy C

Post by syo_astro » January 24th, 2013, 1:47 pm

Orange714 wrote:If they asked you to identify a DSOs based on a light curve or a spectra is there any way to identify it, without having like a picture of it? Like what we've been doing is just finding the spectra/light curve then matching it up...But I'm interested in learning how to identify without having a picture present...is that possible? For some of the DSOs I can't find the light curves/spectra. Kinda rambling sorry XD
Thanks in advance
Certain ones I don't think you could do without the specific light curve...but there are certain characteristic features. For example, a supernova you would know have a peak followed by a descending luminosity. Other variable stars have a generally applicable light curve, cepheids as a major example ;). Supernova you also know have certain elements in their spectra. But aside from that I guess I can't say much more. Anyone else?
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Re: Astronomy C

Post by Orange714 » January 24th, 2013, 3:56 pm

I guess that helps at least narrow it down.
Can anyone help me with a couple math probs?

If Cassiopeia A started expanding in AD 1667 and now has an angular diameter of 3.06' (3.06 arc-minutes), what average velocity has it been expanding at (in km/s)? (Hint: What distance is it to Cassiopeia A?)

A Type I Cepheid is observed to have an average apparent magnitude of 12.7 and a parallax of 0.03296 milli-arc-seconds. What is its period (of varying luminosity) in days?

I don't even know where to start T.T

Thanks!

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Re: Astronomy C

Post by syo_astro » January 24th, 2013, 4:22 pm

Orange714 wrote:I guess that helps at least narrow it down.
Can anyone help me with a couple math probs?

If Cassiopeia A started expanding in AD 1667 and now has an angular diameter of 3.06' (3.06 arc-minutes), what average velocity has it been expanding at (in km/s)? (Hint: What distance is it to Cassiopeia A?)

A Type I Cepheid is observed to have an average apparent magnitude of 12.7 and a parallax of 0.03296 milli-arc-seconds. What is its period (of varying luminosity) in days?

I don't even know where to start T.T

Thanks!
Well, if you want exact work ask, but in the mean time I'll hint you at what I think you should do. For the first one you should probably use the small angle formula to find the size of Cassiopeia and then find the time elapsed from the date they give. Then you just do speed = distance over time. Make sure to keep units right! For the next one you kind of have to work backwards a bit. You should probably use the parallax in d=1/p, use that with the apparent magnitude in the distance modulus, and then take the absolute magnitude from that and put that into the period-luminosity relationship for type I cepheids, while solving for period. Hope that helps!
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Re: Astronomy C

Post by EastStroudsburg13 » January 24th, 2013, 5:51 pm

Darn, syo got there first. :P

Questions like your second one are very typical of Astronomy. You'll get two or three values that aren't directly related, but through using formulae like parallax, the distance modulus, Hubble's Law, what have you, you'll be able to work your way to the answer. Good tests will often have anywhere from 3-10 questions like this, so when looking at formulas try to also see how they go together, so when you encounter these types of problems you'll be able to form a strategy and then dive right in!
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Re: Astronomy C

Post by Orange714 » January 27th, 2013, 7:42 pm

I'm wondering how in depth my knowledge should be of stellar evolution, as I'm studying I'm stumbling across things like electroweak stars or black stars (not dwarf) and Soft X-ray Transients....Does it really just depend on your event supervisors? Thanks!

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Re: Astronomy C

Post by manutd94 » January 27th, 2013, 11:31 pm

Orange714 wrote:I'm wondering how in depth my knowledge should be of stellar evolution, as I'm studying I'm stumbling across things like electroweak stars or black stars (not dwarf) and Soft X-ray Transients....Does it really just depend on your event supervisors? Thanks!
I'd say note the terms down and once you're good on the basics, focus on the more obscure stuff so you can see how they fit in the bigger picture. In-depth stellar evolution info is a necessity if you're aiming to medal. Also, if you don't have time to learn the details, it can't hurt to throw a bit of info about the topics into your binder or on your laptop. You never know what sort of random info you may be asked on astro exams. That's what makes the event so great :D
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