The Crab Nebula is located about 6 x 10¹⁹ meters away. (This is a very difficult quantity to determine, and may well be off by a factor of 2).

Light travels at 3 x 10⁸ m/sec (or about 7 times around the world in one second!) Thus, the length of time it takes light to get here from the Crab Nebula is:

6 x 10¹⁹m/3 x 10⁸ m/sec
or about 2 x 10¹¹ seconds.

This is about 7000 years. Since distances are so vast in the cosmos, astronomers frequently use a unit called the "light year" which is the distance light would travel, in one year. Since the speed of light, c, is about 3 x 10⁸ m/sec and there are about 3 x 10⁷ seconds/year.

1 l y = 10¹⁶ meters. = 6 trillion miles!

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