The Essential Galileo (15 page)

On 9 February at thirty minutes, there were two stars on the east side of Jupiter and one on the west, in an arrangement like this:

The star furthest to the east, which was a rather small one, was four minutes from the next star. The star in the middle was larger and seven minutes from Jupiter. And Jupiter was four minutes from the western star, which was a small one.

On 10 February at one hour and thirty minutes, a pair of stars, very small, and both on the east side of the planet, were visible, in the following configuration:

The further star was ten minutes from Jupiter; the nearer, twenty seconds; and they were in the same straight line. But at the fourth hour the star 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; it was further from Jupiter than before, since its distance was now twelve minutes.

On 11 February at the first hour, there were two stars on the east and one on the west:

The western star was four minutes from Jupiter; the star on the east nearest to the planet was likewise four minutes from Jupiter; and the star further to the east was eight minutes from this one. They were fairly clear to view and in the same straight line. But at the third hour, the fourth star was visible near to Jupiter on the east, less in magnitude than the rest, separated from Jupiter by a distance of thirty seconds, and slightly to the north out of the straight line drawn through the rest:

They were all very bright and extremely distinct. At the fifth hour and a half, the star on the east nearest to Jupiter had moved further away from the planet, [90] and was occupying a position midway between the planet and the neighboring star further to the east. They were all in the same straight line exactly, and of the same magnitude, as may be seen in the following diagram:

On 12 February at forty minutes, a pair of stars on the east and likewise a pair on the west were near the planet:

The star on the east further removed from Jupiter was at a distance of ten minutes, and the further of the stars on the west was eight minutes off. They were both fairly distinct. The other two were very near to Jupiter and very small, especially the star to the east, which was forty seconds from Jupiter; the distance of the western star was one minute. But at the fourth hour, the star that was nearest to Jupiter on the east was no longer visible.

On 13 February at thirty minutes, two stars were visible in the east and two also in the west:

The star on the east near Jupiter was fairly distinct; its distance from the planet was two minutes. The star further to the east was less noticeable; it was four minutes from the other. Of the stars on the west, the one furthest from Jupiter, which was very distinct, was parted from the planet by four minutes. Between this star and Jupiter intervened a small star close to the most westerly star, being not more than thirty seconds off. They were all in the same straight line, corresponding exactly to the direction of the ecliptic.

On 15 February (for on the 14th the sky was covered with clouds) at the first hour, the position of the stars was thus:

That is, there were three stars on the east, but none were visible on the west. The star on the east nearest to Jupiter was fifty seconds from the planet; the next was twenty seconds from this star; and the furthest to the east was two minutes from the second star. The third star was larger than the others, and those nearer to Jupiter were very small. Then about the fifth hour, only one of the stars that had been near to Jupiter was to be seen; its distance from Jupiter was thirty seconds. The distance of the star furthest to the east from Jupiter had increased, for it was then four minutes:

But at the sixth hour, besides the two [91] situated as just described on the east, one star was visible towards the west, very small, at a distance of two minutes from Jupiter:

On February 16, at the sixth hour, their places were arranged as follows: