Scientific notation is used to make large numbers easier to write. For example, the distance from the earth to the the sun is

150000000 km or 1.5 x 10 8 km

This is a very important distance in astronomy and it has a special name, the Astronomical Unit (AU). Distances in the Solar System are usually measured in terms of AU.

Scientific notation can also be used to write very small numbers. The mass of one hydrogen atom is

0.00000000000000000000000000167 kg or 1.67 x 10 -27 kg

Such huge and small numbers occur in astronomy all the time.
In counting all those zeroes above, you might make a mistake, so it is also more reliable to use scientific notation. We know just by looking at the exponent how big, or small, the number is without counting the zeroes. The exponent is called the order of magnitude of the number. The distance to the sun is on the order of 108 km, and the mass of the hydrogen atom is on the order of 10-27 kg. When we look at the order of magnitude of a number, we are just looking at the exponent above the ten, and not at the numbers in front.
Use the following demonstration to become familiar with scientific notation. You can pick up the decimal place and move it through the large number. As you move the decimal point the exponent on the 10 will correct itself so that you will always have the correct abbreviated number in scientific notation. Pay attention to the exponent!
The equality above is always correct because as you lose a power of ten by moving the decimal point to the left you gain that power in the exponent on the ten. Even though all of the different places for the decimal point give you a correct answer the accepted way to do it right is to have the number to the left of the "x 10something" be between 1 and 10. So

14.959787 x 10 7 = 149,597,870

could be better and

0.14959787 x 10 9 = 149,597,870

could be better, too, but

1.4959787 x 10 8 = 149,597,870

is just right.

By making the number to the left of the "x 10something" between 1 and 10 you put all of the powers of ten into the exponent on the 10. That makes is very easy to see the order of magnitude of the number.

A useful abbreviation is to substitute " E " or " e " for " x 10 " as shown below

2.35 x 10 5 = 2.35e5 = 2.35E5

You can use this abbreviation to avoid writing a superscript exponent. Calculators will usually express scientific notation in this way. Every calculator does scientific notation a little differently. If you have a fancy graphing calculator like a TI89 or HP48gII, then you will most likely have to set it to use scientific notation using a menu or mode option. For more simple calculators, there is often a button that switches modes. To enter numbers in scientific notation, look for a button marked EE or Exp. These buttons tell the calculator what the power of ten is.

EXAMPLE: To enter the number 9.989 x 1033 in your calculator, type the following:  "9.989 EE 33" or "9.989 EXP 33".

Be very careful not to confuse EE and Exp with the ex button. The ex button is for Euler's number (which is about 2.718) and tells the calculator that you want to raise 2.718 to some power. Typing "9.989 ex 33" means "9.989 x 2.71833."

Note that 100 is just 1. In fact, any number raised to the power zero is 1.

 

Multiplying and Dividing Numbers in Scientific Notation

To multiply numbers written in scientific notation, consider

10 x 10 x 10 = 10 1 x 10 1 x 10 1 = 1000 = 10 3

The exponents just add.  Likewise,

2 x 10 3 x 4 x 10 -3 = 2000 x 0.004 = 8 = 8 x10 0

which is found by multiplying 2 by 4 and adding the exponents 3 and -3.

Division works the same way, except you subtract the exponents, so

6 x 10 3 / 3 x 10 3 = 6000 / 3000 = 2 = 2 x10 0

which is found by dividing 6 by 3 and subtracting the exponents.

Taking the Tour

Clicking on the "Tour" button above will open a new window with an interactive exercise. You will see an image in the center and a scale bar to the right. Start by clicking the number 1. This will show you an old image of the Astronomy 101 Lab classroom.  Clicking larger numbers will take you further away from the classroom. Below the image you will see some numbers.  For images 0 through 6, these numbers are the distance from the classroom. For the rest of the images, these numbers are the size of the objects shown.  To the right of the image are the words "scientific notation" in green letters. If you click on this link, you will get the number under the image to scientific notation. Notice that the exponent on the ten and the scale number do not always match!