Scientific notation is used to express very large or small numbers. It involves moving the decimal point in a number to the right or left by a power of 10. Positive powers of 10 move the decimal point right to express large numbers, like distances between planets. Negative powers of 10 move the decimal point left to express small decimal numbers, like distances between atoms. To convert a number to scientific notation, the decimal is moved to create a number between 1 and 10, and the power of 10 indicates how many places the decimal was moved.