Question

Why do astronomers use scientific notation to describe sizes?

Answer 1

Please see below.

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

`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.