Name: 為什麼不是每月都有日食？ (Why Aren't There Eclipses Every Month?)
Uploaded: 2025-06-18T17:45:41.000Z
Duration: 2 min 23 s

The moon orbits the earth once per month, which means the moon is on the sun's side of the earth every month.

月球每月繞地球運行一圈，這意味著月球每月都在地球的太陽一側。

情態副詞

So why aren't there eclipses every month is a question answered eloquently in a 1757 astronomy book by James Ferguson.

那麼，為什麼不是每個月都有日食呢？這個問題在 1757 年詹姆斯-弗格森（James Ferguson）的一本天文學書中得到了很好的回答。

It's kind of the 18th century equivalent of astronomy for dummies, complete with amazing illustrations.

這本書相當於 18 世紀的《天文學入門》，配有精彩的插圖。

Here's Ferguson's surprisingly good 250 year old explanation for why there aren't eclipses every month, illustrated by me.

下面是弗格森 250 年前對為什麼不是每月都有日食的驚人解釋，由我繪製插圖。

Every planet and satellite is illuminated by the sun, and casts a shadow towards that point of the heavens which is opposite to the sun.

每顆行星和衛星都受到太陽的照射，並向天空中與太陽相對的那一點投下陰影。

When the sun's light is so intercepted by the moon that to any place of the earth the sun appears partly or wholly covered, he is said to undergo an eclipse, though properly speaking, tis only an eclipse of that part of the earth where the moon's shadow falls.

當太陽光被月亮攔截，以至於地球上任何地方的太陽看起來都被部分或全部遮住時，太陽就被稱為 "日食"，儘管正確地說，這只是月影落在地球上的那一部分的日食。

When the sun is eclipsed to us, the moon's inhabitants on the side next to the earth – if any such there be – see her shadow like a dark spot traveling over the earth, about twice as fast as its equatorial parts move, and the same way as they move.

當太陽對我們來說黯然失色時，在地球旁邊的月球居民--如果有的話--會看到她的影子像一個黑點在地球上移動，速度大約是地球赤道部分移動速度的兩倍，而且與它們移動的方式相同。

If the moon's orbit were coincident with the plane of the ecliptic, in which the earth always moves, the moon's shadow would fall upon the earth at every new moon, and eclipse the sun to some parts of the earth.

如果月球的軌道與黃道面重合，而地球總是在黃道面上運動，那麼每逢新月，月球的影子就會落在地球上，地球上的某些地方就會日食。

But one half of the moon's orbit is elevated 5 degrees above the ecliptic, and the other half is much depressed below it.

但是，月球軌道的一半高出黃道 5 度，而另一半則遠遠低於黃道。

Consequently, the moon's orbit intersects the ecliptic in two opposite points, called the moon's nodes.

是以，月球軌道與黃道相交於兩個相對的點，稱為月球交點。

When these points are in a line with the sun at new or full moon, the sun, moon, and earth are all in a line, and if the moon be then new, her shadow falls upon the earth.

當這些點與新月或滿月時的太陽在一條直線上時，太陽、月亮和地球都在一條直線上，如果當時是新月，她的影子就會落在地球上。

If full, the earth's shadow falls upon her.

如果滿了，地球的影子就會落在她身上。

When the moon is more than 17 degrees from either of the nodes at a new moon, the moon is then too high or too low in her orbit to cast any part of her shadow upon the earth.

在新月時，如果月亮與任何一個交點的距離超過 17 度，那麼月亮在其軌道上就會過高或過低，無法向地球投下任何部分的影子。

But when the moon is less than 17 degrees from either node at the time of conjunction, her shadow falls upon the earth.

但是，當合相時，月亮與任一交點的距離小於 17 度時，她的影子就會落在地球上。

The moon's orbit contains 360 degrees, of which 17 degrees – the limit of solar eclipses on either side of the nodes – is but a small portion, and as the sun passes by the nodes but twice in a year, it is no wonder that we have so many new moons without eclipses.

月球的軌道有 360 度，其中 17 度--交點兩側日食的極限--只是一小部分，由於太陽一年中只經過交點兩次，難怪我們有那麼多沒有日食的新月。

This video was supported in part by NASA's Heliophysics Education Activation Team, which loves solar eclipses.

這段視頻得到了美國國家航空航天局太陽物理學教育激活小組的部分支持，該小組非常喜歡日食。

NASA HEAT's mission is to engage with learners of all ages like you and me, and to deepen our understanding of our closest star and its effects on earth and the solar system.

NASA HEAT 的使命是讓像你我這樣的各年齡段的學習者參與進來，加深我們對離我們最近的恆星及其對地球和太陽系的影響的瞭解。

Solar eclipses are a great way to experience a different side of the sun than we normally do, like literally the corona extending out from its sides.

日食是體驗太陽不同於我們通常所見的另一面的絕佳方式，比如從太陽兩側延伸出來的日冕。

If you ever have the opportunity to see a total eclipse, I highly recommend it.

如果你有機會看到日全食，我強烈推薦你去看。

美國國家航空航天局也是如此。