卷五·第 253–263 问　两弦、法西萨特、月食、日食与视差

§253. What is the nīmbarīn?

第二百五十三问　何谓“宁巴林”？

It is the Moon's being in the fourth sign from the sign of the Sun, at the same number of degrees as the Sun, and it is called the first quarter; that is on about the seventh night of the month. If the Moon is in the tenth sign from the sign of the Sun, at the same number of degrees as the Sun, which is on about the twenty-second night of the month, it is the second quarter. In Persian both are called nīmbarīn, because the light of the Moon in them is on half of its body that is seen, so that it is as if cut in two. The part and the ascendant are worked out for them as they are worked out for the conjunction and the opposition.

它是月亮在从太阳所在星座数起的第四个星座中，度数与太阳相同，称为上弦；那大约在一个月的第七夜。若月亮在从太阳所在星座数起的第十个星座中，度数与太阳相同，那大约在一个月的第二十二夜，就是下弦。在波斯语里两者都称为“宁巴林”，因为此时月亮的光在它可见之体的一半上，好像它被切成两半一样。为它们求度与上升点，同为合与望求的一样。

§254. What are the fāsīsāt?

第二百五十四问　何谓“法西萨特”？

They are distances of the Moon from the Sun that the astrologers watch for, claiming that they are the places of change in the weather, as the seamen keep them in mind; and the angles of illness, I mean the distances taken from the place of the Moon at the onset of the illness at intervals of a sign and a half, which run thus: 45, 90, 135, 180, 225, 270, 315, 360. The fāsīsāt taken from the Sun are the conjunction and the opposition, 12 degrees before and after each of them, 45 degrees before and after each of them, and the first and second quarters. Taken in the order of the signs they are 0, 12, 45, 90, 135, 168, 180, 192, 225, 270, 315, 348.

它们是月亮离太阳的若干距离，占星家留意观察，声称那是天气变化之处，航海的人也把它们记在心里；还有疾病之角，我是指从得病之时月亮所在之处起、每隔一个半星座所取的距离，依次为：四十五、九十、一百三十五、一百八十、二百二十五、二百七十、三百一十五、三百六十。从太阳取的法西萨特是：合与望，各自前后十二度，各自前后四十五度，以及上弦与下弦。按星座次序排列，它们是：零、十二、四十五、九十、一百三十五、一百六十八、一百八十、一百九十二、二百二十五、二百七十、三百一十五、三百四十八。

§255. What is an eclipse of the Moon?

第二百五十五问　何谓月食？

Because the globe of the earth is dark and not transparent, and the rays of the Sun fall on it from one side, its shadow extends to a distance on the side opposite the Sun, after the pattern of what we see of the shadows of dense bodies when they come between a lamp and the walls on which its rays fall. But the earth is a sphere, so its shadow is round; it lies on the zodiac opposite the Sun. So whenever the Moon has no latitude at the time of opposition, it passes through the centre of the circle of the shadow, the earth comes between it and the Sun and cuts off the Sun's light from it, and it is seen in its own colour, devoid of light. If it has latitude, the eclipse or its absence depends on that.

因为地球是暗的、不透光的，而太阳的光线从一侧照到它上面，它的影子便向背着太阳的一侧伸展到一段距离，就像我们所见的浓密物体挡在灯与灯光所照的墙壁之间时投下的影子那样。而地球是球形的，所以它的影子是圆的；它落在黄道上与太阳相对之处。所以，每当望时月亮没有纬度，它就穿过影圈的中心，地球隔在它与太阳之间，切断了太阳照向它的光，它就以自身的颜色、无光地被人看见。若它有纬度，食或不食就取决于纬度。

§256. What effect have the Head and the Tail on it?

第二百五十六问　龙头与龙尾对月食有什么作用？

The latitude of the Moon depends on its distance from the Head or the Tail. If one of them is at the place of the opposition, or near it by less than 12 degrees, the Moon at the time of opposition has no latitude or little, and is near the zodiac; so it enters the shadow wholly or in part. For this reason there is no eclipse of the Moon unless the Head or the Tail is near the Sun.

月亮的纬度取决于它离龙头或龙尾的距离。若两者之一就在望之处，或离它不到十二度，月亮在望时就没有纬度或纬度很小，靠近黄道；于是它全部或部分进入影中。因此，若龙头或龙尾不靠近太阳，就没有月食。

§257. How many kinds of lunar eclipse are there?

第二百五十七问　月食有几种？

An eclipse of the Moon is either of part of its body or of all of it. That which is of all of it either has a stay for some time in that state, or has no stay, but the beginning of the clearing comes with the completion of the eclipse.

月食或是食其本体的一部分，或是食其全体。食其全体的，或在那种状态下停留一段时间，或没有停留，而是食尽之时就是复明之始。

§258. From which side does the eclipse begin?

第二百五十八问　月食从哪一侧开始？

The motion of the earth's shadow along the zodiac is equal to the motion of the Sun, and the Moon, following it, overtakes the circle of the shadow that eclipses it. It is known that the first part of the Moon to reach the shadow is its eastern edge; so the beginning of the eclipse in it is from the side of the east, though not absolutely, for it then deviates a little from due east towards the north or the south. Whoever pictures this knows that the completion of the eclipse in the Moon is on the side of the west, the beginning of the clearing on the side of the east, and the completion of the clearing on the side of the west.

地影沿黄道的运动等于太阳的运动，月亮跟在它后面，追上遮食它的影圈。已知月亮最先到达影子的部分是它的东缘；所以它的食从东侧开始，但不是绝对的，因为那时它会从正东稍偏向北或南。凡能想象此事的人都知道：月亮的食既在西侧，复明之始在东侧，复明完毕在西侧。

§259. How many times has an eclipse of the Moon?

第二百五十九问　月食有几个时刻？

If the eclipse has no stay, or is not total, it has three times: the first is the beginning of the eclipse and the appearance of a notch in the light of the full moon; the second is the middle of the eclipse and the darkness reaching its greatest amount, which is truly the time of the opposition; and the third is the completion of the clearing and the full moon's coming out of the darkness. If the eclipse has a stay, it has five times: the first is the beginning of the eclipse; the second is the completion of the eclipse and the stripping of the light from the full moon, which is the beginning of the time of the stay; the third is the middle of the eclipse, which is also the middle of the time of the stay; the fourth is the end of the stay and the beginning of the clearing; and the fifth is the completion of the clearing. This figure helps in picturing that.

若食没有停留，或不是全食，它有三个时刻：第一是食始，满月的光上出现一个缺口；第二是食中，黑暗达到最大，这才真正是望的时刻；第三是复明完毕，满月从黑暗中出来。若食有停留，它有五个时刻：第一是食始；第二是食既，满月的光被剥尽，这是停留之时的开始；第三是食中，也是停留之时的中间；第四是停留之末，复明之始；第五是复明完毕。这张图有助于想象此事。

§260. Do eclipses of the Moon differ in different towns?

第二百六十问　各城所见的月食是否不同？

Because what befalls the Moon in its eclipse is something that affects its body, its amount is seen in one and the same state, since it takes place at one instant of time. But the hours of the night differ in different towns according to the difference of the rising in them for the Moon's daily orbit, so that in some of them the eclipse is found at a smaller hour and in others at a greater; and it is seen in some towns and not seen in others, because the beginning of the night is not one and the same for them, except by coincidence.

因为月亮在食中所遭的，是影响它本体的事，所以它的食分在各处看去都是同一个样子，因为它发生在同一时刻。但各城的夜间时辰，因月亮周日圈在各地升起的不同而不同，所以在有些城里食落在较早的时辰，在另一些城里落在较晚的时辰；而且有些城看得见，有些城看不见，因为各城的夜晚开始的时刻并不相同，除非碰巧。

§261. What is an eclipse of the Sun?

第二百六十一问　何谓日食？

The Moon is seen at the end of the month in the mornings as a crescent, west of the Sun; then it is seen again as a crescent at the beginning of the next month in the evenings, east of the Sun. In passing from its west to its east it crosses over it, comes between it and our sight, and covers either all of it or part of it. The blackness that is seen on the Sun is the body of the Moon covering it, plainly seen, and that is its own colour.

月亮在月末的清晨被看见是一弯新月，在太阳之西；然后在下个月初的傍晚，又被看见是一弯新月，在太阳之东。它从太阳之西移到太阳之东时，就越过太阳，挡在太阳与我们的视线之间，遮住它的全部或一部分。在太阳上所见的黑色，就是遮住它的月亮本体，清清楚楚，那是月亮自身的颜色。

§262. Does this differ in different towns?

第二百六十二问　日食是否因城而异？

Two differences attach to it there. One is what we mentioned in the eclipse of the Moon, arising from the difference of the rising and of the beginning of the daytime. The second arises from parallax, because the covering body is near us and the hidden body far off, and what overcomes it is nothing in the Sun itself, but only something that befalls our sight. So its times in different towns do not fall at the very same moments of time, but at times that also differ; and the amount of the eclipse differs likewise, so that perhaps in one town half of it is eclipsed, in another a third, in a third the whole, and in some none at all.

这里有两种差异。一种是我们在月食中提到的，出于升起的不同和白昼开始的不同。第二种出于视差，因为遮者离我们近，被遮者离我们远，而遮住太阳的并不是太阳本身的什么变化，只是发生在我们视线上的事。所以它在各城的时刻并不落在同一些时刻，而是落在也各不相同的时刻；食分也同样不同，或许在一城食去一半，在另一城食去三分之一，在第三城全食，在有些城则完全不食。

§263. What is parallax?

第二百六十三问　何谓视差？

Parallax is the seeing of the same thing at the same time in two different places when the place from which it is looked at differs. So the Moon, with respect to the centre of the earth, is seen on the orb at a place other than that in which it is seen from the surface of the earth. For this reason its conjunction with the Sun, when reckoned from the centre of the earth, is called the computed conjunction, and when taken with respect to its surface, the visible conjunction. Their times differ: sometimes the visible precedes the computed, and sometimes it comes after it. In the same way the state of those who look at it from different places differs: the Moon covers the whole of the Sun in one place, part of it in another place, and none of it in yet another. This figure helps in picturing that.

视差是：同一时刻的同一事物，因观看之处不同，而被看在两个不同的地方。所以月亮相对于地心而言，在天球上被看见的位置，不同于从地面上被看见的位置。因此，它与太阳的合，从地心推算时称为推算之合，就地面而言时称为可见之合。两者的时刻不同：可见之合有时先于推算之合，有时在其后。同样，从不同地方看它的人，情形也不同：月亮在一处遮住太阳的全部，在另一处遮住一部分，在又一处一点也不遮。这张图有助于想象此事。