Who said it was only measured as an integer? Seconds are a decimal value and many timekeeping applications require higher precision than to the millisecond. Referencing an epoch closer to our current time allows greater precision with a single double-precision floating point number.
Want to reference something before J2000? Use a negative number.
It’s independent of earth rotation, so no need to consider leap second updates either unless you are converting to UTC. It’s an absolute measure of time elapsed.
Simplicity and precision.
Who said it was only measured as an integer? Seconds are a decimal value and many timekeeping applications require higher precision than to the millisecond. Referencing an epoch closer to our current time allows greater precision with a single double-precision floating point number.
Want to reference something before J2000? Use a negative number.
It’s independent of earth rotation, so no need to consider leap second updates either unless you are converting to UTC. It’s an absolute measure of time elapsed.