What Is the Summer Solstice?何為夏至？

史蒂芬·施耐德 陳棟

The summer solstice1 marks the official start of summer. It brings the longest day and shortest night of the year for the 88 percent of Earth’s people who live in the Northern Hemisphere2. People around the world observe3 the change of seasons with bonfires and festivals and Fête de la Musique4 celebrations.

Astronomers can calculate an exact moment for the solstice， when Earth reaches the point in its orbit where the North Pole is angled closest to the sun. That moment will be at 10：54 a.m. Eastern Time on June 21 this year. From Earth， the sun will appear farthest north relative to the stars. People living on the Tropic of Cancer5， 23.5 degrees north of the Equator6， will see the sun pass straight overhead at noon. Six months from now the sun will reach its southern extreme and pass overhead for people on the Tropic of Capricorn7， and northerners will experience their shortest days of the year， at the winter solstice.

The sun’s angle relative to Earth’s equator changes so gradually close to the solstices that， without instruments， the shift is difficult to perceive for about 10 days. This is the origin of the word solstice， which means “solar standstill8.”

This slow shift means that June 21 is only about 1 second longer than June 20 at mid-northern latitudes. It will be about a week before there’s more than a minute change to the calculated amount of daylight.

Monuments9 at Stonehenge in England， Karnak in Egypt， and Chankillo in Peru reveal that people around the world have taken note of the sun’s northern and southern travels for more than 5，000 years. From Stonehenge’s circle of standing stones， the sun will rise directly over an ancient avenue leading away to the northeast on the solstice. We know little about the people who built Stonehenge， or why they went to such great effort to construct it—moving multi-ton stones from rock outcrops10 as far as 140 miles away. All this to mark the spot on the horizon where the sun returns each year to rest for a while before moving south again. Perhaps they， like us， celebrated this signal of the coming change of seasons.

夏至標(biāo)志著夏天的正式開(kāi)始。地球上88%的人生活在北半球，這一天對(duì)他們而言是一年中白晝最長(zhǎng)、夜晚最短的一天。世界各地的人們會(huì)通過(guò)篝火、節(jié)慶和音樂(lè)節(jié)等方式慶祝這一季節(jié)變換。

天文學(xué)家可以計(jì)算出夏至點(diǎn)的精確時(shí)間，屆時(shí)地球?qū)⒀剀壍肋\(yùn)行至北極點(diǎn)和太陽(yáng)夾角最小的位置。今年的夏至點(diǎn)將發(fā)生在6月21日美國(guó)東部時(shí)間上午10點(diǎn)54分。從地球上看，相對(duì)于其他行星，這一刻太陽(yáng)將出現(xiàn)在最北的位置。生活在北回歸線（赤道以北23.5度）的人們?cè)谡鐣r(shí)將看到太陽(yáng)直射。再過(guò)6個(gè)月，太陽(yáng)將到達(dá)它的南部極點(diǎn)并從南回歸線上的人頭頂掠過(guò)，而北半球的居民將在冬至經(jīng)歷他們一年當(dāng)中最短的白天。

太陽(yáng)相對(duì)于地球赤道的夾角在至點(diǎn)附近變化十分緩慢，以至于如果沒(méi)有儀器，這種移動(dòng)大約10天之內(nèi)都難以察覺(jué)。這也是“至點(diǎn)”這個(gè)詞的由來(lái)——意思就是“太陽(yáng)停滯”。

這一緩慢的移動(dòng)意味著北半球中緯度地區(qū)6月21日白天只比6月20日長(zhǎng)出約一秒。約一周之后，白晝的計(jì)算量才會(huì)有一分鐘以上的變化。

英格蘭的巨石陣、埃及的卡納克神廟、秘魯?shù)牟榛逵^測(cè)臺(tái)，這些歷史遺跡揭示了5000多年前，世界各地的人們便已經(jīng)在記錄太陽(yáng)的南北向之旅。夏至這天，從巨石陣那佇立的石圈看去，太陽(yáng)會(huì)從一條通向東北方向的古道上方升起。我們對(duì)建造巨石陣的人知之甚少，也不了解為何他們要跋山涉水從140英里外的露頭區(qū)搬來(lái)這些數(shù)噸重的巨石來(lái)建造它。所有這一切都為了標(biāo)記出地平線上每年太陽(yáng)都會(huì)回歸并作短暫停留的那個(gè)位置，隨后太陽(yáng)便重又向南移動(dòng)。也許他們也像我們一樣，在慶祝這一季節(jié)變化的標(biāo)志。

（譯者 為“《英語(yǔ)世界》杯”翻譯大賽獲獎(jiǎng)選手）