POSTED: 9:39 p.m. HST, Jun 30, 2012
A 61-second minute happened between 2 and 2:01 p.m. Saturday in Hawaii.
The addition of a “leap second” to the other 86,400 seconds that made up the day was prompted in part by observations from the Kokee Park Geophysical Observatory on Kauai.
Kokee’s sophisticated antenna takes space measurements as part of system conducting what is called very long baseline interferometry.
Interferometry is essentially the same phenomenon that lends depth perception to creatures with multiple eyes: Each eye has a slightly different perspective.
In this case, it tracks how fast the Earth is rotating.
The answer: not fast enough to keep up with atomic clocks.
Kokee and the other stations around the world conduct observations at the same time every day of a selected object called a quasar, short for quasi-stellar radio source. Quasars are essentially motionless as viewed from Earth because they are typically several billion light-years away.
The quasar signal reaches each “eye” or station at a slightly different time.
NASA officials say the miniscule differences in arrival times allow scientists to figure out the positions of the stations and Earth’s orientation in space, as well as calculating Earth’s rotation speed relative to the quasar.
The rotational time can then be compared to atomic clocks, which are far more reliable.
“The solar day is gradually getting longer because Earth’s rotation is slowing down ever so slightly,” Daniel MacMillan of NASA’s Goddard Space Flight Center said in a statement Friday. “At the time of the dinosaurs, Earth completed one rotation in about 23 hours.”
The culprit: the tidal forces of the moon.
About every 100 years, the day gets about 1.4 thousandths of a second longer.
In fact, a day hasn’t been precisely 24 hours long since 1820.
Leap seconds are added to keep the rotational time standard, called Universal Time 1, close to the atomic clocks’ standard, called Coordinated Universal Time (UTC).
Proposals have been made to abolish the leap second and let the two time standards drift apart, but that won’t happen before 2015 because it needs approval from a U.N. agency.