Leap Year - and - Leap Seconds

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From: SFPhysics@aol.com
Date: Fri Nov 21 2003 - 11:29:16 PST 

From: SFPhysics@aol.com
Message-ID: <19e.1d26150e.2cefc18c@aol.com>
Date: Fri, 21 Nov 2003 14:29:16 EST
Subject: Leap Year - and - Leap Seconds

<< did I already ask this? I can't recall...
>In one text it reads that the Earth makes 365.26 rotations in one year. We
>discussed that that the .25 of a rotation adds up every four years to make
>one full day which adds a day to those calendar years named, "Leap Year."
>The hanging question is what do we do with the .01 of a day? After
>centuries upon centuries those hundredths add up to full days too. Hmmmmm.
>Thanks for your thoughts (possibly again) Becca
>>

Hello Rebecca:

The National Bureau of Standards and other nations on the Coordinated
Universal Time Standard (UTC, the old Greenwich Mean Time replacement) adjust the
year by adding leap seconds. The figure quoted in the text was the decimal
equivalent of a complete rotation and was inaccurately rounded up. The 0.01
rotation of 360 degrees gives a figure of 3.6 degrees. The earth turns 15 degrees
in one hour; so, this would mean each year would have a 14.4 minute difference
from the previous year which is clearly not the case.

However, due to tidal forces slowing the earth's rotation there is one on
going time adjustment besides the leap year. It is the leap second. The actual
time discrepancy per year is only about 0.73 second (roughly 2 milliseconds
per day) and leap seconds are added about every 500 days either on Jan 1st or
June 1st. This is to keep astronomical time in line with the UTC time for the
purposes of accurate navigation.

Best wishes to all on the Pinhole List - Have a Happy Thanksgiving -

Al Sefl
Who is also slowing down...

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