一年中日出最早的那天不是夏至

The earliest sunrise of the year isn't on the summer solstice

一年中日出最早的那天不是夏至

The summer solstice, which falls on June 21 in the Northern Hemisphere, offers more total sunlight than any other day of the year. It would seem to make sense, then, for the summer solstice to also feature the year's earliest sunrise and latest sunset.

6月21日是北半球的夏至，這一天的日照總量超過了一年中的任何一天。因此，夏至也有可能是一年中日出最早和日落最晚的一天。

Many people are surprised, however, to learn that isn't quite how it works. While the solstice offers the greatest amount of daylight overall, the earliest sunrise occurs before the solstice and the latest sunset falls afterward. The exact dates vary by latitude, with the year's earliest sunrise and latest sunset occurring further from the solstice date the closer you are to the equator.

然而，許多人驚訝地發(fā)現(xiàn)，事實并非如此。雖然夏至提供了最多的日照，但最早的日出出現(xiàn)在夏至之前，最晚的日落在夏至之后。確切的日期因緯度而異，離赤道越近，一年中最早的日出和最晚的日落發(fā)生的時間就離夏至日越遠。

In Hawaii, for example, the earliest sunset is about two weeks before the summer solstice, and the latest sunset comes about two weeks after, as astronomy writer Bruce McClure explains for EarthSky. At the Northern Hemisphere's mid-northern latitudes, on the other hand, the earliest sunrise will take place June 14 and the latest sunset will follow on June 27.

例如，在夏威夷，最早的日落發(fā)生在夏至前兩周，而最晚的日落發(fā)生在夏至后兩周，天文學(xué)作家布魯斯·麥克盧爾在接受EarthSky采訪時解釋道。另一方面，在北半球的中緯度地區(qū)，最早的日出將在6月14日，最晚的日落將在6月27日。

If you're in the Southern Hemisphere, the June solstice is the shortest day of the year. A city at 40 degrees north latitude (like Philadelphia) will see its earliest sunrise at 5:31 a.m. on June 14, for instance, while a city at 40 degrees south latitude (like Valdivia, Chile) will see its latest sunrise at 8:12 a.m. on the same day.

如果你在南半球，6月至日是一年中白晝最短的一天。比如，北緯40度的城市(像費城)日出時間最早，是6月14日凌晨5點31分，而南緯40度的城市(比如智利瓦爾迪維亞)日出時間最晚，是當(dāng)天早上8點12分。

This is largely due to the tilt of Earth's rotational axis, as astronomer Ken Croswell explains in StarDate magazine, but it's also influenced by our elliptical orbit around the sun, which causes Earth to travel at different speeds throughout the year.

正如天文學(xué)家肯·克羅斯威爾在《StarDate》雜志上解釋的那樣，這在很大程度上是由于地球旋轉(zhuǎn)軸的傾斜，但它也受到我們圍繞太陽的橢圓軌道的影響，這導(dǎo)致地球全年以不同的速度運行。

For a more in-depth explanation, see this breakdown of the phenomenon from the U.S. Naval Observatory (USNO). And to find out when the sun will rise and set where you are, check out this calculator from the USNO's Astronomical Applications Department.

要了解更深入的解釋，請參見美國海軍天文臺(USNO)對這一現(xiàn)象的分析。如果想知道你所在的地方，太陽什么時候會升起，什么時候會落下，請查看美國國家天文臺天文應(yīng)用部的數(shù)據(jù)。