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Important Time Change Notice for Astronomers

Our past president Mike sent us an important notice regarding a time change that will affect everyone’s telescope mounts. Don’t forget because if you don’t, your GoTos will be less accurate (or maybe more accurate?) than usual!!!
USNO Series 14
Date: Mon, 5 Jan 2015 18:52:26 +0000
From: Earth Orientation Dept. USNO

U.S. NAVAL OBSERVATORY
WASHINGTON, D.C. 20392-5420

January 05, 2015
No. 72

TIME SERVICE ANNOUNCEMENT SERIES 14

UTC TIME STEP

1. The International Earth Rotation and Reference Systems Service (IERS) has
announced the introduction of a time step to occur at the end of June, 2015.

2. Coordinated Universal Time (UTC) will be retarded by 1.0s so that the
sequence of dates of the UTC markers will be:

2015 June 30 23h 59m 59s
2015 June 30 23h 59m 60s
2015 July 01 0h 0m 0s

3. The difference between UTC and International Atomic Time (TAI) is:

from 2012 01 Jul, UTC to 2015 01 Jul, UTC: TAI-UTC= +35s
from 2015 01 Jul, UTC until further notice: TAI-UTC= +36s

4. Information regarding current and predicted values of UT1-UTC is provided
in IERS Bulletin A.

5. UTC and all time scales based on UTC will be affected by this adjustment.
However, GPS will not be adjusted physically. For GPS, the leap second
correction contained within the UTC data of subframe 4, page 18 of the
navigation message transmitted by satellites will change.

Before the leap second
GPS-UTC = +16s (i.e., GPS is ahead of UTC by sixteen seconds)

After the leap second
GPS-UTC = +17s (i.e., GPS will be ahead by seventeen seconds)

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