What is an HR diagram and what does it mean to the stars?

Answer 1

A HR diagram(abbreviation of Hertzsprung Russel diagram) is a graph of stars' surface temperatures(x axis) versus their luminosities(y axis). Basically, what we do is observe a lot of stars, find each star's temperature and luminosity and put them all there on the graph. This graph is important in understanding stellar evolution due to a theorem called ergodic theorem. Let us see how.

When a star is born, it has a particular luminosity and temperature. As it lives its life, it's luminosity and temperature keeps changing, and finally it finishes it life. Basically, what I mean is that you take a star when it's born, find its temperature and luminosity, put that on a graph that reads luminosity versus temperature for y and x axis respectively, wait a few million years, see the star again, find it's then temperature and luminosity, put that on that graph, and keep doing it till the star dies. What you get then is a graph that tells you how the star's luminosity and temperature changed as it lived it's life. With luminosity and temperature, you can calculate all other stuff about the star and write down it's biography! Do that with all stars, and you get loads of biographies of different stars, and you become a master of stellar evolution! But wait, there is an issue here...a star typically lives it's life in the order of a billion years. We humans evolved one million years back, we discovered telescopes four hundred years back, and a typical human lives a hundred years, how will we understand stars with such little time?! The answer is HR diagram!!

Now back to ergodic theorem, it says that seeing a thousand stars as they appear to us now and finding their temperature and luminosity and then putting it on HR graph is same as following a star all it's life! Essentially a shortcut to understanding stars! That's the big advantage of HR diagram in studying stars... of course, the focus of my answer was the importance of ergodicity in studying stars but not explaining in detail the concept of ergodicity. That you can find in any statistical mechanics text book or maybe I can explain that somewhere in answers.com soon! Cheers, hope my answer helped!:)

Answer 2

There isn't a lot of interpretation involved. It's basically brightness vs. color; you look at a bunch of stars and put a dot for each one, and when you're done you notice that they tend to fall into "clumps". You then give names to each of these clumps, and Bob's your uncle (bonus points if your names match the established ones, like "giants", "supergiants", "main sequence" et al.).

Answer 3

Luminosity, heat, and location.

Answer 4

by heat and temperature