Andrew Yee[_1_]
December 31st 08, 06:00 AM
U.S. Naval Observatory
Washington, D.C.
Information Contact:
Geoff Chester
USNO Public Affairs Office
(202) 762-1438
Dr. Dennis McCarthy
U.S. Naval Observatory
(202) 762-1837
For Immediate Release: December 8, 2008
U.S. Naval Observatory to Add Leap Second to Clocks
On December 31, 2008 a "leap second" will be added to the world's clocks at
23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC). This
corresponds to 6:59:59 pm Eastern Standard Time, when the extra second will
be inserted at the U.S. Naval Observatory's Master Clock Facility in
Washington, DC. This marks the 24th leap second to be added to UTC, a
uniform time-scale kept by atomic clocks around the world, since 1972.
Historically, time was based on the mean rotation of the earth relative to
celestial bodies and the second was defined in this reference frame.
However, the invention of atomic clocks defined a much more precise "atomic
time" scale and a second that is independent of the earth's rotation. In
1970, an international agreement established two timescales: one based on
the rotation of the earth and one based on atomic time. The problem is that
the earth's rotation is very gradually slowing down, which necessitates the
periodic insertion of a "leap second" into the atomic timescale to keep the
two within 1 second of each other. The International Earth Rotation and
Reference Systems Service (IERS) is the organization which monitors the
difference in the two timescales and calls for leap seconds to be inserted
or removed when necessary. Since 1972, leap seconds have been added at
intervals varying from six months to seven years, with the last being
inserted on December 31, 2005.
The U.S. Naval Observatory is charged with the responsibility for the
precise determination and dissemination of time for the Department of
Defense and maintains its Master Clock. The U.S. Naval Observatory,
together with the National Institute of Standards and Technology (NIST),
determines time for the United States. Modern electronic navigation and
communications systems depend increasingly on the dissemination of precise
time through such mechanisms as the Internet-based Network Time Protocol
(NTP) and the satellite-based Global Positioning System (GPS).
The U.S. Naval Observatory is the largest single contributor to the
international time scale (UTC), which is computed in Paris, France, at the
International Bureau of Weights and Measures. This international prominence
in atomic timekeeping is due to the sheer number of atomic clocks operated
by the Observatory and the fidelity to which they are maintained. Moreover,
the U.S. Naval Observatory's principal role in keeping track of changes in
the "Earth clock" (i.e., Earth rotation) and its dissemination of this
information as the Rapid Service/Prediction Center for the IERS attests to
the fact that globally, as well as nationally, the U.S. Naval Observatory
remains the leader in precise time.
Information concerning the U.S. Naval Observatory, its mission, history, and
programs is available from our World Wide Web site at
http://www.usno.navy.mil
Washington, D.C.
Information Contact:
Geoff Chester
USNO Public Affairs Office
(202) 762-1438
Dr. Dennis McCarthy
U.S. Naval Observatory
(202) 762-1837
For Immediate Release: December 8, 2008
U.S. Naval Observatory to Add Leap Second to Clocks
On December 31, 2008 a "leap second" will be added to the world's clocks at
23 hours, 59 minutes and 59 seconds Coordinated Universal Time (UTC). This
corresponds to 6:59:59 pm Eastern Standard Time, when the extra second will
be inserted at the U.S. Naval Observatory's Master Clock Facility in
Washington, DC. This marks the 24th leap second to be added to UTC, a
uniform time-scale kept by atomic clocks around the world, since 1972.
Historically, time was based on the mean rotation of the earth relative to
celestial bodies and the second was defined in this reference frame.
However, the invention of atomic clocks defined a much more precise "atomic
time" scale and a second that is independent of the earth's rotation. In
1970, an international agreement established two timescales: one based on
the rotation of the earth and one based on atomic time. The problem is that
the earth's rotation is very gradually slowing down, which necessitates the
periodic insertion of a "leap second" into the atomic timescale to keep the
two within 1 second of each other. The International Earth Rotation and
Reference Systems Service (IERS) is the organization which monitors the
difference in the two timescales and calls for leap seconds to be inserted
or removed when necessary. Since 1972, leap seconds have been added at
intervals varying from six months to seven years, with the last being
inserted on December 31, 2005.
The U.S. Naval Observatory is charged with the responsibility for the
precise determination and dissemination of time for the Department of
Defense and maintains its Master Clock. The U.S. Naval Observatory,
together with the National Institute of Standards and Technology (NIST),
determines time for the United States. Modern electronic navigation and
communications systems depend increasingly on the dissemination of precise
time through such mechanisms as the Internet-based Network Time Protocol
(NTP) and the satellite-based Global Positioning System (GPS).
The U.S. Naval Observatory is the largest single contributor to the
international time scale (UTC), which is computed in Paris, France, at the
International Bureau of Weights and Measures. This international prominence
in atomic timekeeping is due to the sheer number of atomic clocks operated
by the Observatory and the fidelity to which they are maintained. Moreover,
the U.S. Naval Observatory's principal role in keeping track of changes in
the "Earth clock" (i.e., Earth rotation) and its dissemination of this
information as the Rapid Service/Prediction Center for the IERS attests to
the fact that globally, as well as nationally, the U.S. Naval Observatory
remains the leader in precise time.
Information concerning the U.S. Naval Observatory, its mission, history, and
programs is available from our World Wide Web site at
http://www.usno.navy.mil