The sidereal messenger of Galileo Galilei : $b and a part of the preface to Kepler's Dioptrics containing the original account of Galileo's astronomical discoveriesGalilei, Galileo
History
The sidereal messenger of Galileo Galilei : $b and a part of the preface to Kepler's Dioptrics containing the original account of Galileo's astronomical discoveries
Galilei, Galileo
Astronomy -- Early works to 1800; Jupiter (Planet) -- Satellites
Jan. 16.—At the first hour of the night I saw three satellites arranged
in this order (Fig. 9). Jupiter was between two of them, which were at
a distance of 0´ 40´´ from the planet on either side, and the third was
west of Jupiter at a distance of 8´. The satellites near to Jupiter
appeared brighter than the satellite further off, but not larger.
Jan. 17, after sunset 0 hours 30 minutes, the configuration was of
this kind (Fig. 10). There was one satellite only to the east, at a
distance of 3´ from Jupiter; to the west likewise there was only one
satellite, distant 11´ from Jupiter. The satellite on the east appeared
twice as large as the satellite to the west; and there were no more
than these two. But four hours after, that is, nearly at the fifth
hour, a third satellite began to emerge on the east side, which, before
its appearance, as I think, had been joined with the former of the two
other satellites, and the position was of this kind (Fig. 11). The
middle satellite was very near indeed to the satellite on the east,
and was only 20´´ from it; and was a little towards the south of the
straight line drawn through the two extreme satellites and Jupiter.
Jan. 18, at 0 h. 20 m. after sunset, the appearance was such as this
(Fig. 12). The satellite to the east was larger than the western one,
and was at a distance from Jupiter of 8´, the western one being at a
distance of 10´.
Jan. 19.—At the second hour of the night the relative position of
the satellites was such as this (Fig. 13); that is, there were three
satellites exactly in a straight line with Jupiter, one to the east, at
a distance of 6´ from Jupiter; between Jupiter and the first satellite
to the west in order, there was an interval of 5´; this satellite was
4´ off the other one more to the west. At that time I was doubtful
whether or no there was a satellite between the satellite to the east
and Jupiter, but so very close to Jupiter as almost to touch the
planet; but at the fifth hour I saw this satellite distinctly, by
that time occupying exactly the middle position between Jupiter and
the eastern satellite, so that the configuration was thus (Fig. 14).
Moreover, the satellite which had just come into view was very small;
yet at the sixth hour it was nearly as large as the rest.
Public-domain text, read in full here on John Shaqi.
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