How can they tell how far away are things like stars, galaxys, quasars, and gamma rays.?
This is very difficult. Stars first. You observe a star, noting it’s position with respect to other stars. You repeat the observation 6 months later. In 6 months, the Earth has moved nearly 200 million miles. If the star has moved, you can figure out what angle it has moved, and figure out how far away it is. It’s a little more complicated than this. The angles are really small. If you know how bright a star should be, and you observe how bright it actually is, you can work out how far away it is. There is a class of stars called Cepheid Variable Stars. These brighten and dim in a way that tells you how bright they are intrinsically. There are a few nearby examples whose distance has been worked out by parallax. Some of these stars are bright enough that they can be picked out in nearby galaxies. This gives you the distance to the galaxy. Some nova and supernova can also give you distance via brightness. With the distance to a number of galaxies known, the relationship of red shift to
This is a very good question, and there’s no one answer for each phenomena Close stars can be determined by parallax. Parallax is the process by which you judge distance. Basically, when you look at a sign, you can “move” the object by closing one eye at a time. It works the same, but instead of eyes, we use telescopes, and instead of winking, we simply wait six months to be on the other side of the planet. Using Geometry, we can figure out the distance to near-by stars. Galaxies and Quasars are different, and I’ll review one of these methods. Gamma Rays are light particles, so they aren’t objects we look at, but rather what we detect from something else. Spectroscopy is the most common method. You basically identify the absorption lines of some element or another, (calcium or hydrogen are the one’s I’ve seen in school) and you can tell how much the lightwave has been shifted from normal. There are three others, but I can’t remember them in detail enough. Hopefully this answers some of
