April 3, 2020

Astro Event of the Week: December 29th, 2008-January 4th, 2009: The Leap Second Strikes!

Revelers this New Years’ Eve can party a bit longer, thanks to the timely (bad pun) addition of a leap second on Dec 31st. The addition of a leap second is due to anomalies in the rotation of the Earth, such as the gravitational drag of the Sun and Moon, the motion of the oceans and tectonic plates, and other complex wackiness.

This will be the first leap second inserted by the International Earth Rotation & Reference System Service (…and they know how to party!) since 2005. The actual leap second occurs on 23:59:60 Universal Time…cheers!

This week’s astro-phrase of the week is Delta-T. Seen in equations as “?”, this represents the cumulative deference between Universal Time and Terrestrial time, and is usually expressed as a value of about 2.3 milliseconds/per day/per century. Folks that do work that involve precession timing, such as computer engineers, may grumble that such occasional changes are necessary to keep our calendar in sync with reality, but hey, the universe is a complex place!

If you can pick up the AM time transmission out of fort Collins, Colorado, you can “observe” the leap second by counting the 61 successive clicks! They transmit on AM frequencies 2.5, 5, 10, 15, 20 MHz. don’t forget the universal time off-set!



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