[LEAPSECS] Cost: getting rid of GMT & discontinuing leap seconds

Rob Seaman seaman at noao.edu
Sun Oct 24 19:53:54 EDT 2010

Poul-Henning Kamp wrote:

> Why did astronomers use UTC as timescale in their systems, where UT1 should have been used?

Astronomers "since time immemorial" have used mean solar time. GMT, a standard international zero-point, was codified in 1884 (Steve will correct me). Universal Time (UT) is a term of art that arose at some later point (but well before leap seconds). UTC (and UT1) are realizations of UT. As the original UTC standard (predating the ITU-R) stated: "GMT may be regarded as the general equivalent of UT."

Astronomers use both UTC and the general notion of UT. Sometimes they use UT1. We use numerous other timescales that aren't based on mean solar time, too.

The heart of my argument remains that civil timekeeping is mean solar time. Astronomers are just caught in the crossfire.


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