Commonly used units
Units commonly used for Earth orientation:
1 mas = 1 milliarcsecond = 1 thousandth of a second of arc (for polar
motion & nutation);
1 ms = 1 millisecond = 1 thousandth of a second of time (for
UT1);
1 mas equals an equatorial shift at the Earth's surface of 3.1 cm;
1 ms equals the time it takes for the Earth to spin 15 mas (46.5 cm at the
equator)
