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 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 seconds). This should help when thinking about periods of time that have different orders of magnitude.