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
Feb. 15 (for on the 14th the sky was covered with clouds), at the
first hour, the position of the satellites was thus (Fig. 47); that
is, there were three satellites on the east, but none were visible
on the west. The satellite on the east nearest to Jupiter was at a
distance of 0´ 50´´ from the planet; the next in order was 0´ 20´´
from this satellite, and the furthest to the east was 2´ from the
second satellite, and it was larger than the others, for those nearer
to Jupiter were very small. But about the fifth hour only one of the
satellites which had been near to Jupiter was to be seen; its distance
from Jupiter was 0´ 30´´. The distance of the satellite furthest to the
east from Jupiter had increased, for it was then 4´ (Fig. 48). But at
the sixth hour, besides the two situated as just described on the east,
one satellite was visible towards the west, very small, at a distance
of 2´ from Jupiter (Fig. 49).
Feb. 16: 6 h.—Their places were arranged as follows (Fig. 50); that is,
the satellite on the east was 7´ from Jupiter, Jupiter 5´ from the next
satellite on the west, and this 3´ from the remaining satellite still
further to the west. They were all of the same magnitude nearly, rather
bright, and in the same straight line, corresponding accurately to the
direction of the Zodiac.
Feb. 17: 1 h.—Two satellites were in view, one on the east, distant 3´
from Jupiter; the other on the west, distant 10´ (Fig. 51). The latter
was somewhat less than the satellite on the east; but at the sixth
hour the eastern satellite was nearer to Jupiter, being at a distance
of 0´ 50´´, and the western satellite was further off, namely 12´. At
both observations they were in the same straight line with Jupiter, and
were both rather small, especially the eastern satellite in the second
observation.
Feb. 18: 1 h.—Three satellites were in view, of which two were on
the west and one on the east; the distance of the eastern satellite
from Jupiter was 3´, and of the nearest satellite on the west 2´; the
remaining satellite, still further to the west, was 8´ from the middle
satellite (Fig. 52). They were all in the same straight line exactly,
and of about the same magnitude. But at the second hour the satellites
nearest to the planet were at equal distances from Jupiter, for the
western satellite was now also 3´ from the planet. But at the sixth
hour the fourth satellite was visible between the satellite on the east
and Jupiter, in the following configuration (Fig. 53). The satellite
furthest to the east was at a distance of 3´ from the next in order;
this one was at a distance of 1´ 50´´ from Jupiter; Jupiter was at a
distance of 3´ from the next satellite on the west, and this 7´ from
the satellite still further to the west. These were nearly equal in
magnitude, only the satellite on the east nearest to Jupiter was a
little smaller than the rest, and they were all in the same straight
line parallel to the ecliptic.
Public-domain text, read in full here on John Shaqi.
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