卷五·第 264–267 问　日食的时刻与方位、为何不每月皆食、掩星

§264. How many times has an eclipse of the Sun?

第二百六十四问　日食有几个时刻？

They are three, since it has no perceptible stay, nor anything at all besides the beginning of the eclipse, its middle, and the completion of the clearing.

有三个，因为它没有可感知的停留，除了食始、食中与复明完毕之外，别的一概没有。

§265. From which side does it begin?

第二百六十五问　日食从哪一侧开始？

Because the body that eclipses the Sun is the Moon, and its course is faster, it overtakes the Sun from the side of the west, and its first contact with it is from that side. So the beginning of an eclipse of the Sun is from the side of the west and the completion of the clearing from the side of the east, which is the opposite of the case of an eclipse of the Moon. Then, if it deviates a little from due east and west, it does not leave those sides.

因为遮食太阳的天体是月亮，而月亮的行程较快，它从西侧追上太阳，它与太阳的最初接触就在那一侧。所以日食从西侧开始，复明完毕在东侧，与月食的情形相反。再者，即使它从正东正西稍有偏离，也不会离开这两侧。

§266. Why is the Sun not eclipsed at every conjunction, and the Moon at every opposition?

第二百六十六问　为什么太阳不在每次合时都食，月亮不在每次望时都食？

Because an eclipse of the Sun is accomplished only when the Moon has no latitude or little, so that it can thereby come between the Sun and the sight. For this reason the condition laid down for the conjunction is that the Head or the Tail be near it, stated loosely and without a fixed limit, so that the Moon's latitude comes out as we have said. For when the two nodes are far from the conjunction, the amount of the Moon's latitude becomes great, and it moves away from the middle that brings about the covering of the Sun, towards the north or the south. The case is the same with the opposition: the Moon is not always eclipsed in it, because it moves away from the circle of the shadow through the greatness of its latitude.

因为日食只有当月亮没有纬度或纬度很小、因而能挡在太阳与视线之间时才会成就。因此为合所定的条件是龙头或龙尾靠近它——这只是笼统地说，没有定下确定的界限——好让月亮的纬度如我们所说的那样。因为当两个交点离合很远时，月亮纬度的量就变大，它便离开造成遮掩太阳的那条中线，偏向北或南。望的情形也一样：月亮在望时并不总是被食，因为它由于纬度大而离开了影圈。

§267. Does eclipse befall anything other than the two luminaries?

第二百六十七问　除两颗发光体以外，还有别的星被食吗？

The Moon eclipses the wandering planets and some of the fixed stars when its passage happens to be over them. It covers them on its eastern side, and then they appear from its western side as if coming out of it; and how often that is seen! The wandering planets also eclipse one another and eclipse some of the fixed stars, so that the two stars become one star. The Sun covers them with its rays, so that no distinction is made in it between what is eclipsed and what is not. But that a planet should be seen beneath the Sun, having an effect on it, does not happen.

月亮在行经游星与某些恒星之上时，就会遮食它们。它在自己的东侧遮住它们，然后它们从它的西侧出现，好像从它里面出来一样；这种情形是多么常见啊！游星也彼此遮食，并遮食某些恒星，于是两颗星变成一颗星。太阳则用它的光线遮住它们，所以在太阳那里，被食的与未被食的无从区分。至于看见一颗行星在太阳之下、对太阳有所作用，那是不会发生的。