Exponental notation
Astronomy concerns itself both with the very large and very small. In
order to describe very large and very small quantities, it is
necessary to use exponental notation.
The distance for earth to Proxima Centuri is 43,000,000,000,000 km.
It is far easier to write this in the form 4.3 x 10^13 km. Similarly
0.0000004 is more easily written 5 x 10^-7.