The light from stars can tell us what type of star it is (our Sun is a G type), the stars spectrum can tell us what elements are in the star, and its intristic brightness can help us determine how...
Well it's pretty simple, you know what a parallax is, as you experience it all the time. Like your in the car, and your moving... you can see the stationary objects closer to you seem to be moving...
Almost everything.
The main thing is that the size dictates the rate of fuel consumption (larger stars using more fuel). So a larger star will burn hydrogen faster (and hence it will be brighter and...
You need a stronger telescope than ordinary telescopes to see if one is a binary star. Like, you can't get these kind in shops… you have to make them, probably:-)
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