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Astronomy 161 – Introduction to Solar System Astronomy
Winter Quarter 2008 – Prof. Martini
Math and Units Review
Scientific Notation
Scientific notation is a compact way of expressing very large and very small numbers and there are
plenty of such numbers in Astronomy. A number in scientific notation consists of two parts: the
mantissa
and the exponent
. The mantissa is simply a decimal number with some number of significant
digits, while the exponent contains the power of ten that the mantissa is multiplied by.
One area where we will use scientific notation is to describe distances. For example, the average
distance between the Earth and Sun is 149,600,000 kilometers (km). In scientific notation this number
is more briefly written as 1.496 x 10
8
km. That is,
1.496 x 10
8
= 149,600,000.
In this number “1.496” is the mantissa and “8” is the exponent.
Very small numbers can similarly be expressed with scientific notation by using a negative exponent.
For example, the size of a Hydrogen atom is 0.0000000000106 meters (m). In scientific notation this
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 Winter '08
 MARTINI
 Solar System

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