leap second 復習

世界の標準時を地球の自転に合わせるために、1日を1秒だけ長くする「うるう秒」が昨日の午前9時に行われました。

Last day of June was one second longer

Many people didn’t notice, but the last day in June was just a little bit longer than in years past.
A “leap” second was added Tuesday to compensate for the slowing speed of the Earth’s rotation around the Sun.
“Earth’s rotation is gradually slowing down a bit, so leap seconds are a way to account for that,” said Daniel MacMillan from NASA.
A typical day lasts 86,400 seconds, but June 30 got a little extension because of a gravitational brake being applied by the moon onto the Earth’s orbit, scientists said.

http://www.japantoday.com/smartphone/view/world/last-day-of-june-was-one-second-longer

今回取り上げるのは、“leap second”という表現です。The Free Dictionary by FARLEXで調べてみると、“A second of time, as measured by an atomic clock, added to or omitted from official timekeeping systems periodically to compensate for small changes in the rotation of the earth and therefore the length of a solar day”と載っており、「うるう秒」を表していることが分かります。
また、「うるう年」などの「うるう」に“leap”が用いられている理由は、うるう年でない年では1年ずつ曜日が1つだけずれていきますが、うるう年では曜日が2つずれてしまい、曜日を1つ「飛び越してしまう」というところにあるようです。(ninetails)