To compare numbers written in scientific notation we must first follow the rules given to us in the following lessons:

Scientific Notation for Large Numbers and 
Scientific Notation for Small Numbers

Example 1:

Earth is  km from the sun and Neptune is km from the sun.  Which planet is closest to the sun?

Solution:

The first step is to write the numbers is standard form.

We can now compare the numbers.  Since 57, 910, 000 km is a smaller number than 108, 200, 000 km Neptune is closer to the sun than Earth.

Example 2:

The surface area of the Earth is square miles.  The volume of all the water on Earth is cubic miles.  Which is the larger number?

Solution:

We must first write the numbers in standard form:

We can now compare the numbers and since 340, 000, 000 is larger than 196, 000, 000 so  is the greater number.

Example 3:

What comparison symbol would we use:

Solution:

Write the numbers in standard form.

Since 0.0045 is larger than 0.00027 the appropriate comparison symbol to use is the "greater than" symbol (>).

For review on comparing decimal numbers go to Ordering Decimals.

Remember:
To compare numbers written in scientific notation, first write the numbers in standard form, then compare.