Total solar eclipses have struck awe or fear into hearts for millennia, but scientists are more interested in the unusual mathematics behind the gold-and-indigo lightshow.

長達數千年時間，日全蝕讓人們心生敬畏或感到恐懼，不過科學家更有興趣知道，由金色轉為靛藍色的日蝕燈光秀背後，有什麼奇特的數學原理。 

Superstition has always haunted the moment when Earth, Moon and Sun are perfectly aligned. The daytime extinction of the Sun, the source of all life, is associated with war, famine, flood and the death or birth of rulers.

當地球、月亮和太陽完全排成一直線的時刻，總是充斥各種迷信。明明是大白天，萬物的根源「太陽」卻消失不見，人類因而將之與戰爭、飢荒、水災、死亡或統治者的誕生聯想在一起。 

 Desperate for an explanation, the ancient Chinese blamed a Sun-eating dog. The Vikings believed the culprits were two giant wolves, Skoll and Hati, which chased the Sun around the sky. Among Indians in South America, an eclipse was simply, terrifyingly, "the Eye of God."

古代的中國人亟欲解釋這種異象，因此將此歸咎於「天狗食日」。維京人相信，造成這種天象的元兇，是兩隻在空中追逐太陽的巨狼「史庫爾」和「哈提」。印地安人和南美人則認為日蝕根本就是可怕的「神之眼」。 

But a remarkable act of celestial geometry explains it all.

不過，天體力學中一種重要的活動可以解釋這一切。 

When the Moon glides between Earth and the Sun, it casts a cone-shaped shadow, called an umbra, that races from West to East.

當月球運行至地球和太陽的中間，會形成圓錐狀的陰影，稱之為「本影」，移動路線由西向東。 

The Sun is 400 times wider than the Moon, but it is also 400 times farther away. Because of the symmetry, the umbra, for those on the planetary surface, is exactly wide enough to cover the face of the Sun.

太陽的寬度是月球的400倍，但太陽和地球的距離也是月球的400倍。由於對稱的關係，對面日地表上的觀測者而言，「本影」的寬度恰好足以蓋住太陽。 

At an eclipse's height, a halo of gold, called a corona, flares around the darkened lunar disc, while the sky turns an eerie dark blue, disorienting birds and causing bats to emerge from their roosts in the belief that night has fallen.

「蝕甚」發生時，稱之為「日冕」的金色光圈，會在陰暗的月球外圍散發光芒，此時天空變成陰森的深藍色，動物誤以為黑夜降臨，鳥類因此無法分辨日夜，蝙蝠也傾巢而出。  

Total solar eclipses are exceptional events, and the one that crosses Asia today is especially so. 全日蝕是非常罕見的天象，今天在亞洲地區出現的日全蝕現象更是如此。 

If the clouds hold back, it could be the most-watched eclipse in history, for its path of totality traverses the world's two most populous countries, China and India. 如果沒有雲層遮蔽，這次日蝕可能會是有史以來最多人看得到的日蝕，因為這次的日全蝕帶橫跨世界上人口最多的兩個國家：中國和印度。 

People living outside totality, from Japan in the north to parts of Indonesia in the south, will be in the penumbra, or partial shadow, which means a "bite" seems to have been taken out of the Sun.

從北邊的日本到南邊的印尼部份地區，居住在日全蝕帶外側的人將受到「半影」遮蔽，看見太陽好像被「吃」掉了一角。  

Until now, the most-watched eclipse occurred on August 11, 1999, when the umbra raced from Britain, across Western Europe, part of the Middle East and India.

目前為止，最多人看見的日蝕發生在1999年8月11日，當時本影跨過英國、西歐，通過中東及印度部分地區。