地球白天時間越來越長 670萬年增加1分鐘

Earth's days are getting longer but you're not likely to notice any time soon — it would take about 6.7 million years to gain just one minute, according to a study published last Wednesday.

據上週三公佈的一份報告顯示，地球的白天時間正在變得越來越長，不過人類很難感覺到--因爲大約要等670年才增加1分鐘。

Over the past 27 centuries, the average day has lengthened at a rate of about +1.8 milliseconds (ms) per century, a British research team concluded in the journal Proceedings of the Royal Society A.

據英國一研究團隊在《英國皇家學會學報》上發佈的報告稱，在最近的27個世紀裏，每個世紀的白晝平均延長了大約1.8毫秒。

This was "significantly less", they said, than the rate of 2.3 ms per century previously estimated — requiring a mere 5.2 million years to add one minute.

該小組的研究人員明確指出，這“大大少於”之前被認爲的每個世紀增加2.3毫秒。人們當時認爲“只”需520萬年就會增加一分鐘。

"It's a very slow process," study lead co-author Leslie Morrison, a retired astronomer with Royal Greenwich Observatory, told AFP.

報告的作者之一、皇家格林尼治天文臺退休天文學家萊斯.莫里森向法新社透露："這是一個非常緩慢的過程"。

"These estimates are approximate, because the geophysical forces operating on the earth's rotation will not necessarily be constant over such a long period of time," he specified. "Intervening Ice Ages etcetera will disrupt these simple extrapolations."

他解釋說，"這個預估只是相近的，因爲推動地球自轉的力量在如此長的一段時間內並非一成不變。冰河時代的干預等其他因素會打破這些簡單的推理。"

The previous 2.3 ms estimate had been based on calculations of the moon's known earth-braking forces, causing the ocean tides.

之前估算的2.3秒的結果就是基於已知的月球引力引起海洋潮汐來預估的。

Factors which influence the earth's rotation include the moon's braking effect, earth's altering shape due to shrinking polar ice caps since the last Ice Age, electro-magnetic interactions between the mantle and core, and changes in the mean sea level, said the team.

該團隊表示，影響地球轉動的因素包括月球的制動力，自冰河世紀以來極地冰川消融造成的地球形狀的改變，地幔和地核的電磁相互作用以及海平面的變化等。