Aristotle thought that the Sun was a fiery ball that moved around the Earth, and then about 100 years later Aristarchus came up with the theory that it wasn't the Sun that moved around us, but us moving around the sun. His idea was rejected at the time. How could we be moving and not feel it? It wasn't until about 400 years later that Ptolemy came up with the theory that the Sun, Stars and planets move around Earth in circles using "Epicycles- We now know that it is a combination of many things, such as that the Earth along with all the other planets orbit around the sun and that each of those planets have separate moons that orbit us all while we rotate ourselves.
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Only until recently we have been able to find out how to decipher distance in space. Because the universe is so big, it was difficult before. You can't really take a big measuring stick and touch the sun or a planet or a moon, or you couldn't drive to mars to find out, A because the distances we travel upon the surface of earth are nothing in comparison to the distances in space, and B there is so much space and so little time. Even if we could somehow drive our "floating car- throughout space, it would take many, many lifetimes to get there. Now however we have space shuttles that can exit our atmosphere and go on the very short journey to our moon. One way we calculate distance is to send out a radar beam and calculate how long it takes to return. However again this is nothing in comparison to the area we would need to cover. The distance to our moon from earth is not even a footstep in comparison to the amount of the universe we still need to see. The way we measure distance in space is in Astronomical Units (AU's) within relation to the sun. For example the distance from the Earth to the Sun is 150,000,000 kilometers (93,000,000 miles) so that is equal to 1 AU. Mars is approximately 1.5 AU's because it is 1 and ½ times the distance from the Earth to the sun.