Astronomy C

[Magikarpmaster629]

Do Type II Cepheids have a longer period than Type I?

I don't think they can, although this graph may not show everything.

[bhavjain]

Here's my question:



(a) What do the colored lines represent?
(b) Rank A, B, C, and D in terms of mass
(c) What is the x-coordinate of the point labeled 2015, in Kelvin?

Going to move my question to this thread: what is this?
(...)

This is a plot of surface gravity (on the y axis) vs. temperature (on the x axis) of post AGB stars on their way to becoming the central star of a planetary nebula. The lines show different evolutionary tracks over time for post AGB stars of different masses.

More massive stars are (in general) hotter, which is why the more massive stars are on the left, and vice versa

By knowing the surface gravity, it also gives us properties like the radius (size) and luminosity.

You might be wondering what the g/(cm/s^2) stuff is. Initially, it may look like grams/(cm/s^2), but the argument of a logarithm should be dimensionless - that is, the units should cancel out in order for the logarithm to make sense. When it says "g", they don't mean g for "gram", they mean "g" for surface gravity, like g = -9.8 m/s^2 for Earth. It's hard to know that they're talking about that type of "g" though, but you can still figure it out. Since the argument of the logarithm has to be dimensionless, you know that whatever "g" is must have the same dimensions as "cm/s^2", which is just acceleration. Personally, when I see "g" and the units for acceleration, it's clear as to what it's trying to say. Additionally, log(g) is a common term in astronomy (I think, at least; Wikipedia says surface gravity is often expressed as log(g): https://www.wikiwand.com/en/Surface_gravity). You'l notice that's why plots have things like log(T_effective/K); the K is to get rid of the unit on the temperature.

Magikarpmaster asked about this in the question marathon thread too; I'll post some more stuff there too

How do you get the temperature of the x-coordinate? Sorry, new to Astro

[Adi1008]

How do you get the temperature of the x-coordinate? Sorry, new to Astro

The x coordinate shows what log(T/K)* is equal to. For example, if the x coordinate is 10, then that means that log(T/K) = 10, so T = 10^10 Kelvin (that's really hot!).

Applying this to the plot... the point has an x coordinate of around 4.7, so that means log(T/K) = 4.7. Recall that just saying "log" means the base is 10, so that means the temperature is 10^4.7 Kelvin. Plugging this into a calculator gives you about 50118 Kelvin, which is the answer.

*Remember that the T/K business just means the natural log of the temperature, in Kelvin. The "/K" is to get rid of the unit (Kelvin), but I've seen it written without the "/K" as well. If it makes it easier to think about, just think of it as taking the natural log of a number (so it would have no units)

Hope this helps!

[EastStroudsburg13]

Generally, I don't see it written all within the same paretheses like that, because of the confusion it causes, but in this case at least the variable is italicized and the units are not. Remember when writing T/K, it's not actually a fraction. It's more like T {K}.

[bhavjain]

Is it possible to derive the distance modulus formula from the inverse square law and other laws?

[Adi1008]

Is it possible to derive the distance modulus formula from the inverse square law and other laws?

It's derived here: https://somewhatoverwhelmed.wordpress.c ... e-modulus/

Forgive me for using my own post, but I feel as if it's explained well in it

[gryphaea1635]

Is there a good textbook to use for studying for this event?

[Magikarpmaster629]

Is there a good textbook to use for studying for this event?

Not really.

There's Carrol and Ostlie's Introduction to Modern Astrophysics, which is good if you're generally interested in astronomy, but doesn't have a whole lot on the topics for the Astronomy event. Also it's very expensive.

A Student's Guide to the Mathematics of Astronomy here is a good introduction to the math portion of the event, but definitely does not include all of the math needed for the event.

There could be more textbooks I'm not aware of, but I mostly use online resources.

[eris_joseph]

new to this event. if anyone has site recommendations or tips that would be great.

[lumosityfan]

new to this event. if anyone has site recommendations or tips that would be great.

Hello eris_joseph! And welcome to Astronomy! Hope you have fun with this event; I know I have! First, some sites I like to use for the Deep Sky Objects are the NASA Astronomy Picture of the Day, the Chandra Telescope website, and the Hubble website. On those websites, you can search up each DSO and find articles about them that'll tell you lots about what the objects are, their characteristics, and why they're important. In addition, you can get the pictures of the objects as well as find out in what wavelength they're taken in. Sometimes a question might ask you in what wavelength the picture was taken in and why that's important and those websites can help you out in that regard. In addition, I would recommend just practice practice practice! Use flashcards to make sure you understand the formulas and why they're important, including (and probably most importantly) in what situations you would use them. For instance, I might write a flashcard on the Stefan-Boltzmann Law, say that it's important for analyzing blackbody radiation and write down the formula so that I don't have to dig through my formula sheet the day of. (As much as that sheet's helpful, it can also be painful if you don't know what you're looking for!) In addition, I would recommend categorizing a lot of the material depending on what they're about, so for instance one category could be mathematical calculations on distances and binary orbits, one category could be about the deep sky objects, and one category could be about stellar evolution and its characteristics. Hope that helps and good luck with all your Astronomy endeavours! And if you need any more, I and a bunch of the other astro/physics people (syo, Alpha, Karp, foreverphysics, East, etc. I'm sure I'm missing some) would be glad to help; just give us a notice and we'll do our best to help!