In modern times with the power of technology we are finally starting to grasp the immense size of the Universe, and it is much bigger than anyone could have ever imagined. Scientists use something called Parallax . Parallax means simply that they look at how much the stars move in the sky back and forth throughout the year as the Earth circles the Sun. This is not something unfamiliar to you. In fact if you stretch out your hand in front of you and look at your thumb, while covering one eye, and than the other, your thumb will appear to move back and forth.
Stars do the same thing, but our eyes are much to close to see the difference.
However If we take a picture while on one side of Earths orbit, and than take another when we get to the opposite side of the orbit, than we have a large enough distance that we can see the stars parallax, and determine how far away they really are. In this picture you can see a man taking a nap after enjoying a nice lunch. Now we zoom out so that we can see 100 times as much. Before we could only see the man and a few things around him, but now you can see every thing on his blanket, and much of the grass. As we zoom out again, this time 10,000 times bigger than the first picture we notice that the man is lying near a busy road and a boating dock.