Transcript: Astronomers have to deal with very large and very small numbers. As we deal with things as low density as the vastness of space and as high density as the center of a black hole, as hot as the first instant after the big band and as cold as intergalactic space, we are dealing with very large and very small numbers. Scientific notation is a short hand for writing very big and very small numbers. For instance, the nearest stars are about 4 or 5 trillion miles or kilometers away. 4 or 5 trillion is 4 or 5 followed by twelve zeros. So scientists use a shorthand form of writing this large number, 4*1012 or 4 times 10 with 12 as an exponent. If the number is very small the exponent has a negative sign in front of it. In science in general and in astronomy in particular we need scientific notation as a quick and efficient way of writing and manipulating large and small numbers.