The sidereal messenger of Galileo Galilei

by Galileo Galilei; Johannes Kepler

Feb. 1.—At the second hour of the night the arrangement was similar ([Fig. 31]). The satellite furthest to the east was at a distance of 6´ from Jupiter, and the western satellite 8´. On the east side there was a very small satellite, at a distance of 20´´ from Jupiter. They made a perfectly straight line.

Feb. 2.—The satellites were seen arranged thus ([Fig. 32]). There was one only on the east, at a distance of 6´ from Jupiter. Jupiter was 4´ from the nearest satellite on the west; between this satellite and the satellite further to the west there was an interval of 8´; they were in the same straight line exactly, and were nearly of the same magnitude. But at the seventh hour four satellites were there—two on each side of Jupiter ([Fig. 33]). Of these satellites, the most easterly was at a distance of 4´ from the next; this satellite was 1´ 40´´ from Jupiter; Jupiter was 6´ from the nearest satellite on the west, and this one from the satellite further to the west, 8´; and they were all alike in the same straight line, drawn in the direction of the Zodiac.

Feb. 3: 7 h.—The satellites were arranged in the following way ([Fig. 34]):—The satellite on the east was at a distance of 1´ 30´´ from Jupiter; the nearest satellite on the west, 2´, and there was a long distance, 10´, from this satellite to the satellite further to the west. They were exactly in the same straight line, and of equal magnitude.

Feb. 4: 2 h.—Four satellites attended Jupiter, two on the east and two on the west, arranged in one perfectly straight line, as in the adjoining figure ([Fig. 35]). The satellite furthest to the east was at a distance of 3´ from the next satellite. This one was 0´ 40´´ from Jupiter; Jupiter 4´ from the nearest satellite on the west; and this one from the satellite further to the west 6´. In magnitude they were nearly equal; the satellite nearest to Jupiter was rather smaller in appearance than the rest. But at the seventh hour ([Fig. 36]) the eastern satellites were at a distance of only 0´ 30´´ apart. Jupiter was 2´ from the nearest satellite on the east; and from the satellite on the west, next in order, 4´; this one was distant 3´ from the satellite further to the west. They were all equal in magnitude, and in a straight line, drawn in the direction of the ecliptic.

Feb. 5.—The sky was cloudy.

Feb. 6.—Two satellites only appeared, with Jupiter between them, as is seen in the accompanying figure ([Fig. 37]). The satellite on the east was 2´ from Jupiter, and that on the west 3´. They were in the same straight line with Jupiter, and were equal in magnitude.

Feb. 7.—There were two satellites by the side of Jupiter, and both of them on the east of the planet, arranged in this manner ([Fig. 38]). The intervals between the satellites and Jupiter were equal, and of 1´ each; and a straight line would go through them and the centre of Jupiter.

Feb. 8: 1 h.—Three satellites were there, all on the east side of Jupiter, as in the diagram ([Fig. 39]). The nearest to Jupiter, a rather small one, was distant from the planet 1´ 20´´; the middle one was 4´ from this satellite, and was rather large; the satellite furthest to the east, a very small one, was at a distance of 0´ 20´´ from this satellite. It was doubtful whether there was one satellite near to Jupiter or two, for sometimes it seemed that there was another satellite by its side towards the east, wonderfully small, and only 10´´ from it. They were all situated at points in a straight line drawn in the direction of the Zodiac. At the third hour the satellite nearest to Jupiter was almost touching the planet, for it was only distant 10´´ from it; but the others had become further off, for the middle one was 6´ from Jupiter. At length, at the fourth hour, the satellite which was previously the nearest to Jupiter joined with the planet and disappeared.

Feb. 9: 0 h. 30 m.—There were two satellites on the east side of Jupiter, and one on the west, in an arrangement such as this ([Fig. 40]). The satellite furthest to the east, which was a rather small one, was distant 4´ from the next satellite; the satellite in the middle was larger, and at a distance of 7´ from Jupiter. Jupiter was distant 4´ from the western satellite, which was a small one.

Feb. 10: 1 h. 30 m.—A pair of satellites, very small, and both on the east of the planet, were visible, in the following position ([Fig. 41]). The further satellite was distant from Jupiter 10´, the nearer 0´ 20´´, and they were in the same straight line; but at the fourth hour the satellite nearest to Jupiter no longer appeared, and the other seemed so diminished that it could scarcely be kept in sight, although the atmosphere was quite clear, and the satellite was further from Jupiter than before, since its distance was now 12´.