Attosecond
An attosecond (as) is a very short period of time. It is equal to one quintillionth of a second (or 0.000000000000000001 seconds). It can also be written as 10−18 seconds. Because it can be hard to think about how short this period of time is, on this page is a list of descriptions of periods of time longer than 1 attosecond, but shorter than one femtosecond (which is 10−15 seconds). This should help when thinking about periods of time that have different orders of magnitude.