Astronomy C

[UTF-8 U+6211 U+662F]

Hello! I'm thinking of doing Astro next year, is there anything I can do to start preparing now even though we don't know the topics will be?

[Unome]

Hello! I'm thinking of doing Astro next year, is there anything I can do to start preparing now even though we don't know the topics will be?

The 2017 and 2018 topics sort of form the baseline for other years, you could probably study that info in slightly less depth to get a good sense of the basics.

[Selundar]

Hello! I'm thinking of doing Astro next year, is there anything I can do to start preparing now even though we don't know the topics will be?

A good chunk of Astronomy stays the same every year. The main parts that change are the DSOs and the sub-topic, but stellar evolution and the math portions are pretty consistent. So for stellar evolution, you should probably look into HR diagrams and spectral classes, low mass vs high mass evolution, supernovae, and stellar remnants (white dwarfs, neutron stars, and black holes). For the math, it would probably be best to look up all the terms listed in the rules to get the equations for them and you can use any test you have access to within the last several years to get practice. Hope this helps!

[Zxcvbnm123]

How do you do question 16 and 17 on the Golden Gate Invitational Test? https://drive.google.com/drive/folders/ ... MRmlHdJc2u

Also, how do you calculate distances to Cepheid and RR Lyrae Stars?

[syo_astro]

How do you do question 16 and 17 on the Golden Gate Invitational Test? https://drive.google.com/drive/folders/ ... MRmlHdJc2u

Also, how do you calculate distances to Cepheid and RR Lyrae Stars?

Have you given those questions a start or have work you can share to check over? That usually makes the checking/explaining go faster.

In the mean time, I'll start things off with 16a. RR Lyrae stars have a period-luminosity relationship that indicates they have an ~constant absolute magnitude (or luminosity) across a range of periods. IF for whatever reason you know you have an RR Lyrae star, you therefore know its absolute magnitude.

Rant about finding this RR Lyrae abs mag (Click to Show Hidden Text)

You can google for the value, but keep in mind usually the numbers listed will vary. Also, there are some finer details and different types that add a bit of an error bar on the value you'll find anyway. Practically for the test, some writers have answer ranges anyway, so just pick a value and go with it (unless someone has studied this very deeply..). You can also ask the proctor / explain the range of values...I haven't really run into issues with this, but usually others ask or worry more about that, so others can feel free to chime in.

Anyway, once you get your absolute magnitude, we remember that we need distance (in pc). We are also given apparent magnitude of the star. If you have apparent magnitude and the absolute magnitude of a star, you can use the distance modulus to find the distance in pc.

Does this help?

[Zxcvbnm123]

How do you do question 16 and 17 on the Golden Gate Invitational Test? https://drive.google.com/drive/folders/ ... MRmlHdJc2u

Also, how do you calculate distances to Cepheid and RR Lyrae Stars?

Have you given those questions a start or have work you can share to check over? That usually makes the checking/explaining go faster.

In the mean time, I'll start things off with 16a. RR Lyrae stars have a period-luminosity relationship that indicates they have an ~constant absolute magnitude (or luminosity) across a range of periods. IF for whatever reason you know you have an RR Lyrae star, you therefore know its absolute magnitude.

Rant about finding this RR Lyrae abs mag (Click to Show Hidden Text)

You can google for the value, but keep in mind usually the numbers listed will vary. Also, there are some finer details and different types that add a bit of an error bar on the value you'll find anyway. Practically for the test, some writers have answer ranges anyway, so just pick a value and go with it (unless someone has studied this very deeply..). You can also ask the proctor / explain the range of values...I haven't really run into issues with this, but usually others ask or worry more about that, so others can feel free to chime in.

Anyway, once you get your absolute magnitude, we remember that we need distance (in pc). We are also given apparent magnitude of the star. If you have apparent magnitude and the absolute magnitude of a star, you can use the distance modulus to find the distance in pc.

Does this help?

I tried doing that, but the answer I am getting (around 70,000) is no where near close to the actual answer.

[Unome]

How do you do question 16 and 17 on the Golden Gate Invitational Test? https://drive.google.com/drive/folders/ ... MRmlHdJc2u

Also, how do you calculate distances to Cepheid and RR Lyrae Stars?

Have you given those questions a start or have work you can share to check over? That usually makes the checking/explaining go faster.

In the mean time, I'll start things off with 16a. RR Lyrae stars have a period-luminosity relationship that indicates they have an ~constant absolute magnitude (or luminosity) across a range of periods. IF for whatever reason you know you have an RR Lyrae star, you therefore know its absolute magnitude.

Rant about finding this RR Lyrae abs mag (Click to Show Hidden Text)

You can google for the value, but keep in mind usually the numbers listed will vary. Also, there are some finer details and different types that add a bit of an error bar on the value you'll find anyway. Practically for the test, some writers have answer ranges anyway, so just pick a value and go with it (unless someone has studied this very deeply..). You can also ask the proctor / explain the range of values...I haven't really run into issues with this, but usually others ask or worry more about that, so others can feel free to chime in.

Anyway, once you get your absolute magnitude, we remember that we need distance (in pc). We are also given apparent magnitude of the star. If you have apparent magnitude and the absolute magnitude of a star, you can use the distance modulus to find the distance in pc.

Does this help?

I tried doing that, but the answer I am getting (around 70,000) is no where near close to the actual answer.

Try an absolute magnitude in the range of 0.55. That said, I took a look at the problem and the answer key seems a bit off to me - it would imply that an RR Lyrae star has an absolute magnitude in the range of 11 to 12.

[antoine_ego]

Have you given those questions a start or have work you can share to check over? That usually makes the checking/explaining go faster.

In the mean time, I'll start things off with 16a. RR Lyrae stars have a period-luminosity relationship that indicates they have an ~constant absolute magnitude (or luminosity) across a range of periods. IF for whatever reason you know you have an RR Lyrae star, you therefore know its absolute magnitude.

Rant about finding this RR Lyrae abs mag (Click to Show Hidden Text)

You can google for the value, but keep in mind usually the numbers listed will vary. Also, there are some finer details and different types that add a bit of an error bar on the value you'll find anyway. Practically for the test, some writers have answer ranges anyway, so just pick a value and go with it (unless someone has studied this very deeply..). You can also ask the proctor / explain the range of values...I haven't really run into issues with this, but usually others ask or worry more about that, so others can feel free to chime in.

Anyway, once you get your absolute magnitude, we remember that we need distance (in pc). We are also given apparent magnitude of the star. If you have apparent magnitude and the absolute magnitude of a star, you can use the distance modulus to find the distance in pc.

Does this help?

I tried doing that, but the answer I am getting (around 70,000) is no where near close to the actual answer.

Try an absolute magnitude in the range of 0.55. That said, I took a look at the problem and the answer key seems a bit off to me - it would imply that an RR Lyrae star has an absolute magnitude in the range of 11 to 12.

In general, I use an average absolute magnitude of +0.75 for RR Lyrae variables based off of Wikipedia. I agree with Unome though, the answer key is wrong on this, since reverse engineering their answer gives me +11.58 as their absolute magnitude, which is less than even the Sun.

[syo_astro]

Sent some emails, double checked myself, indeed the key has a mistake. The answers should be about
(a) 70,795 pc
(b) 0.014 mas

So the 70,000 pc is basically correct...the previous two posts also agree with my point about not just assuming "the wiki value is right" and searching around a little or asking. Besides, the citation for the wiki value still works, and it's important to note there is an errorbar even on that average value...statistics are tricky!

Hope that helps.

[SciolyHarsh]

On the golden gate test, how would you do 17 c, d, and f?