# Why do astronomers use scientific notation to describe sizes?

Mar 10, 2018

#### Explanation:

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

$150000000 \times 30 \times 8766 = 39447000000000$ 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 $93 , 000 , 000 , 000 \times 9861750000000$

= $917142750000000000000000$ 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.