Why do astronomers use scientific notation to describe sizes?
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Astronomers use scientific notation to describe sizes as sizes very a lot. For example, distance to moon is #385,000# kilometers, but distance to Sun is about #150,000,000# kilometers (this is known as AU - Astronomic Unit of distance) and average distance of Neptune, farthest planet is #30# AU or #4,500,000,000# kilometers and it may take just around #4# hours for light to reach Neptune.
Now compare it with the nearest star Proxima Centauri, which is at a distance of four light-years and as in one year there are about #8766# hours, the distance to Proxima Centauri is about #8766# times the one to Neptune or in kilometers it will be
#150000000xx30xx8766=39447000000000# kilometers.
This is still very small as compared to size of universe. For example, the bulge at the center of milky way is about #12000# light years or #3000# times distance to Proxima Centauri.
Further the observable universe spans some #93# billion light-years in diameter, as it is still expanding i.e.
about #93,000,000,000xx9861750000000#
= #917142750000000000000000# kilometers
A similar scale may apply to volumes, mass and number of stellar objects. It is for these reasons that astronomers use scientific notation to describe sizes.
