[time-nuts] GPS/UTC time

[Brian Inglis]

On 2015-07-04 07:36, Jim Lux wrote:
> On 7/3/15 9:45 PM, Brek Martin wrote:
>> I feel like I missed “The Big Thing” in time keeping land. I should have watched my Ublox LEA-5T.
>> What is the difference if it is in the reporting mode for GPS or UTC time?
>> If they skip a second UTC, surely the GPS time isn’t run incorrectly forever.

> Who's to say which is "correct", UTC or GPS?
> GPS time is derived from TAI; both are monotonically increasing, continuous, and constant rate.  These are nice attributes for something you're going to use for time stamping, or controlling.  No gaps, no jumps, etc.
> UTC (and local civil time, and GMT, etc.) have leap seconds, to adjust the time scale to the motion of the Earth;  so that the sun is highest at noon (after accounting for the equation of time).
> While that's somewhat convenient, I doubt anyone would really object to noon being a few tens of seconds away from the zenith crossing when standing on the line. TAI is ahead of UTC by 36 seconds.  They add a leap second every year and a half, so I guess in 100 years, we'll have drifted some minute or so away.  (the earth has slowed down in the last 200 years.. a day is now 86400.0015 seconds long, although it's faster now than it was in the 70s, when it was 86400.003 seconds)
> http://tycho.usno.navy.mil/leapsec.html
> (the Japan earthquake in 2011 sped the earth up by 1.8 microseconds/day.  The Sumatra quake on 26 Dec 2004 had a bigger effect: 6.8 microseconds)

By my calculations, that should mean the earth rotated 3mm farther/day at the equator after Sumatra.
Anyone know if, or how much, these perturbations affect the orbit of the earth or other planets, or where to find out?

-- 
Take care. Thanks, Brian Inglis