The Sidereal Messenger: the Moons of Jupiter
星际信使：木星的卫星
原题：Sidereus Nuncius（拉丁语）
伽利略·伽利莱 Galileo Galilei（1564–1642）
译者：Edward Stafford Carlos（1842–1927），1880 年
1610 年

冷冻图书馆 · 开架书库 · S-006006 · https://coldlibrary.com/s/006006
权利：拉丁文原著 1610 年出版，伽利略卒于 1642 年。译者卡洛斯是基督公学的教师，卒于 1927 年（维基数据 Q26156392）；译本出版于 1880 年。已按澳大利亚、欧盟、英国、中国大陆和美国的规则核对（截至 2026 年 10 月 11 日）。仅供参考，不是法律意见。
来源：Project Gutenberg，https://www.gutenberg.org/cache/epub/46036/pg46036.txt（取于 2026-10-11）
中文译文：Claude（AI），2026 · CC0 1.0
生成于 2026-10-14，来自 https://coldlibrary.com/open-stacks/galileo-sidereal-messenger-jupiter

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The discovery

There remains the matter, which seems to me to deserve to be considered the most important in this work, namely, that I should disclose and publish to the world the occasion of discovering and observing four PLANETS, never seen from the very beginning of the world up to our own times, their positions, and the observations made during the last two months about their movements and their changes of magnitude; and I summon all astronomers to apply themselves to examine and determine their periodic times, which it has not been permitted me to achieve up to this day, owing to the restriction of my time. I give them warning however again, so that they may not approach such an inquiry to no purpose, that they will want a very accurate telescope, and such as I have described in the beginning of this account.

On the 7th day of January in the present year, 1610, in the first hour of the following night, when I was viewing the constellations of the heavens through a telescope, the planet Jupiter presented itself to my view, and as I had prepared for myself a very excellent instrument, I noticed a circumstance which I had never been able to notice before, owing to want of power in my other telescope, namely, that three little stars, small but very bright, were near the planet; and although I believed them to belong to the number of the fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line, parallel to the ecliptic, and to be brighter than the rest of the stars, equal to them in magnitude. The position of them with reference to one another and to Jupiter was as follows.

On the east side there were two stars, and a single one towards the west. The star which was furthest towards the east, and the western star, appeared rather larger than the third.

I scarcely troubled at all about the distance between them and Jupiter, for, as I have already said, at first I believed them to be fixed stars; but when on January 8th, led by some fatality, I turned again to look at the same part of the heavens, I found a very different state of things, for there were three little stars all west of Jupiter, and nearer together than on the previous night, and they were separated from one another by equal intervals, as the accompanying illustration shows.

At this point, although I had not turned my thoughts at all upon the approximation of the stars to one another, yet my surprise began to be excited, how Jupiter could one day be found to the east of all the aforesaid fixed stars when the day before it had been west of two of them; and forthwith I became afraid lest the planet might have moved differently from the calculation of astronomers, and so had passed those stars by its own proper motion. I therefore waited for the next night with the most intense longing, but I was disappointed of my hope, for the sky was covered with clouds in every direction.

But on January 10th the stars appeared in the following position with regard to Jupiter; there were two only, and both on the east side of Jupiter, the third, as I thought, being hidden by the planet. They were situated just as before, exactly in the same straight line with Jupiter, and along the Zodiac.

When I had seen these phenomena, as I knew that corresponding changes of position could not by any means belong to Jupiter, and as, moreover, I perceived that the stars which I saw had been always the same, for there were no others either in front or behind, within a great distance, along the Zodiac,—at length, changing from doubt into surprise, I discovered that the interchange of position which I saw belonged not to Jupiter, but to the stars to which my attention had been drawn, and I thought therefore that they ought to be observed henceforward with more attention and precision.

Accordingly, on January 11th I saw an arrangement of the following kind, namely, only two stars to the east of Jupiter, the nearer of which was distant from Jupiter three times as far as from the star further to the east; and the star furthest to the east was nearly twice as large as the other one; whereas on the previous night they had appeared nearly of equal magnitude. I therefore concluded, and decided unhesitatingly, that there are three stars in the heavens moving about Jupiter, as Venus and Mercury round the Sun; which at length was established as clear as daylight by numerous other subsequent observations. These observations also established that there are not only three, but four, erratic sidereal bodies performing their revolutions round Jupiter, observations of whose changes of position made with more exactness on succeeding nights the following account will supply. I have measured also the intervals between them with the telescope in the manner already explained. Besides this, I have given the times of observation, especially when several were made in the same night, for the revolutions of these planets are so swift that an observer may generally get differences of position every hour.

Jan. 12.—At the first hour of the next night I saw these heavenly bodies arranged in this manner. The satellite furthest to the east was greater than the satellite furthest to the west; but both were very conspicuous and bright; the distance of each one from Jupiter was two minutes. A third satellite, certainly not in view before, began to appear at the third hour; it nearly touched Jupiter on the east side, and was exceedingly small. They were all arranged in the same straight line, along the ecliptic.

Jan. 13.—For the first time four satellites were in view in the following position with regard to Jupiter.

There were three to the west, and one to the east; they made a straight line nearly, but the middle satellite of those to the west deviated a little from the straight line towards the north. The satellite furthest to the east was at a distance of 2´ from Jupiter; there were intervals of 1´ only between Jupiter and the nearest satellite, and between the satellites themselves, west of Jupiter. All the satellites appeared of the same size, and though small they were very brilliant, and far outshone the fixed stars of the same magnitude.


What the observations show

These are my observations upon the four Medicean planets, recently discovered for the first time by me; and although it is not yet permitted me to deduce by calculation from these observations the orbits of these bodies, yet I may be allowed to make some statements, based upon them, well worthy of attention.

And, in the first place, since they are sometimes behind, sometimes before Jupiter, at like distances, and withdraw from this planet towards the east and towards the west only within very narrow limits of divergence, and since they accompany this planet alike when its motion is retrograde and direct, it can be a matter of doubt to no one that they perform their revolutions about this planet, while at the same time they all accomplish together orbits of twelve years’ length about the centre of the world. Moreover, they revolve in unequal circles, which is evidently the conclusion to be drawn from the fact that I have never been permitted to see two satellites in conjunction when their distance from Jupiter was great, whereas near Jupiter two, three, and sometimes all (four), have been found closely packed together. Moreover, it may be detected that the revolutions of the satellites which describe the smallest circles round Jupiter are the most rapid, for the satellites nearest to Jupiter are often to be seen in the east, when the day before they have appeared in the west, and contrariwise. Also the satellite moving in the greatest orbit seems to me, after carefully weighing the occasions of its returning to positions previously noticed, to have a periodic time of half a month. Besides, we have a notable and splendid argument to remove the scruples of those who can tolerate the revolution of the planets round the Sun in the Copernican system, yet are so disturbed by the motion of one Moon about the Earth, while both accomplish an orbit of a year’s length about the Sun, that they consider that this theory of the constitution of the universe must be upset as impossible; for now we have not one planet only revolving about another, while both traverse a vast orbit about the Sun, but our sense of sight presents to us four satellites circling about Jupiter, like the Moon about the Earth, while the whole system travels over a mighty orbit about the Sun in the space of twelve years.

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中文译文 · Claude（AI）译

发现

还剩下一件事，我认为它应当被看作这部著作中最重要的事：那就是向世界公开宣布，我是在什么机缘下发现并观察到四颗从开天辟地直到我们这个时代都无人见过的行星的，并公布它们的位置，以及过去两个月里对它们的运动和亮度变化所作的观测。我还要请所有天文学家都来致力于考察、确定它们的周期，由于时间所限，直到今天我还没能做到这一点。不过我要再次提醒他们，以免他们徒劳地着手这项研究：他们需要一架非常精确的望远镜，就像我在这篇报告开头所描述的那样。

今年，即1610年的1月7日，夜里第一个钟头，我正用望远镜观看天上的星座，木星出现在我的视野中。由于我已为自己准备了一件非常出色的仪器，我注意到了一个从前因另一架望远镜倍率不够而始终没能注意到的情形：在这颗行星旁边有三颗小星，很小，但非常亮。我虽然相信它们属于恒星之列，它们却让我有些纳闷，因为它们似乎恰好排在一条直线上，与黄道平行，而且比同等星等的其他恒星更亮。它们彼此之间以及与木星的相对位置如下。

东边有两颗星，西边只有一颗。最东边的那颗和西边的那颗，看上去比第三颗稍大一些。

我几乎完全没有留意它们与木星之间的距离，因为正如我已经说过的，起初我相信它们是恒星；但到了1月8日，不知受了什么命运的牵引，我又去看天空的同一处，却发现情形大不相同：三颗小星都在木星的西边，彼此比前一夜靠得更近，而且相互间隔相等，如附图所示。

这时，虽然我还完全没有去想这些星彼此靠近的事，我的惊讶却开始被激起：木星怎么会前一天还在其中两颗星的西边，这一天却到了所有这些“恒星”的东边？我立刻担心起来，怕这颗行星的运动与天文学家的推算不同，是凭它自己的运动越过了那些星。于是我怀着最强烈的渴望等待下一夜，但我的希望落空了，因为天空四面八方都布满了云。

到了1月10日，这些星相对于木星出现在这样的位置：只有两颗，都在木星东边；我想，第三颗是被这颗行星挡住了。它们的位置和以前一样，恰好与木星在同一条直线上，沿着黄道。

看到这些现象之后，我知道这样相应的位置变化绝不可能属于木星；而且我察觉到，我所看到的始终是同样那几颗星，因为沿着黄道，在很远的范围之内，前后都没有别的星。于是，我终于由怀疑转为惊奇，发现我所看到的位置交换不属于木星，而属于引起我注意的那几颗星；因此我认为，从此以后应当更加用心、更加精确地观察它们。

于是，在1月11日，我看到了这样的排列：木星东边只有两颗星，较近的那颗与木星的距离，是它与更东边那颗星之距离的三倍；最东边的那颗星差不多比另一颗大一倍，而前一夜它们看上去大小几乎相等。于是我断定，并毫不犹豫地确认：天上有三颗星在绕着木星运动，就像金星和水星绕着太阳运动一样。后来又经过许多次观测，这一点终于像白昼一样清楚地确立了。这些观测还确立了：绕木星运转的游移星体不是三颗，而是四颗。随后几夜对它们位置变化所作的更精确的观测，见下文的记录。我还用前面说明过的方法，以望远镜测量了它们之间的间隔。此外，我给出了观测的时刻，尤其是同一夜作了几次观测的时候，因为这些行星运转得极快，观测者通常每个小时都能看到位置的不同。

1月12日。——次夜第一个钟头，我看到这些天体是这样排列的。最东边的卫星比最西边的卫星大，但两颗都非常显眼、明亮；每一颗与木星的距离都是两分。第三颗卫星此前肯定看不见，到第三个钟头才开始出现；它在东侧几乎贴着木星，极其微小。它们全都排在同一条直线上，沿着黄道。

1月13日。——第一次同时看到了四颗卫星，它们相对于木星的位置如下。

西边三颗，东边一颗；它们几乎排成一条直线，只是西边三颗中居中的那一颗稍稍偏离直线，偏向北方。最东边的卫星距木星2´；木星与最近的那颗卫星之间，以及木星西边各卫星彼此之间，间隔都只有1´。所有卫星看上去大小相同，虽然很小，却非常明亮，远比同等星等的恒星耀眼。


观测所揭示的

以上就是我对四颗美第奇行星的观测，它们是最近才由我第一次发现的。虽然我还不能根据这些观测推算出这些天体的轨道，但或许可以容我依据它们，说几点很值得注意的话。

首先，它们时而在木星之后，时而在木星之前，距离相仿，向东、向西离开这颗行星都只在很窄的范围之内；而且无论木星逆行还是顺行，它们都同样伴随着它。因此谁也不会怀疑，它们是在绕着这颗行星运转，同时又一起以十二年的周期绕宇宙的中心运行。其次，它们沿着大小不等的圆周运转；这显然可以从下面的事实推出：在离木星很远的地方，我从来没能看到两颗卫星相合，而在木星附近，却曾见到两颗、三颗，有时是全部（四颗）紧紧挤在一起。还可以看出，绕木星画出最小圆周的卫星运转得最快，因为最靠近木星的卫星常常前一天还在西边，第二天就出现在东边，反之亦然。至于在最大轨道上运行的那一颗，我仔细权衡了它回到先前所见位置的各个时机之后，觉得它的周期约为半个月。此外，我们还有一个出色而辉煌的论据，可以打消一些人的疑虑：他们能够接受哥白尼体系中行星绕太阳运转，却因为一个月亮绕着地球运动、而两者又一起以一年为期绕太阳运行，便大感困扰，以致认为这种宇宙构造的学说必须作为不可能之事予以推翻。如今我们看到的，已不只是一颗行星绕着另一颗运转、而两者一起绕太阳走过一条巨大的轨道；我们的眼睛亲自向我们展示了四颗卫星绕着木星转，如同月亮绕着地球，而整个系统又在十二年间绕太阳走过一条宏大的轨道。