Year
In astronomy, the Julian year is a unit of time; it is defined as 365.25 days of exactly 86,400 seconds (SI base unit), totalling exactly 31,557,600 seconds in the Julian astronomical year.
Atomic clock
For context, a femtosecond () is to a second what a second is to about 31.71 million () years and an attosecond () is to a second what a second is to about 31.71 billion () years.