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. 28: 1 h.—Only two satellites were visible, one on the east, at a
distance of 9´ from Jupiter, and another on the west, at a distance of
2´; they were both rather bright, and in the same straight line with
Jupiter, and a straight line drawn from the fixed star perpendicular
to this straight line fell upon the satellite on the east, as in the
figure (Fig. 61). At the fifth hour a third satellite was seen at a
distance of 2´ from Jupiter, on the east, in the position shown in the
figure (Fig. 62).
March 1: 0 h. 40 m.—Four satellites, all on the east of the planet,
were seen; the satellite nearest to Jupiter was 2´ from the planet;
the next 1´ from this; the third was 0´ 20´´ from the second, and was
brighter than the others; and the satellite still further to the east
was at a distance of 4´ from it, and was smaller than the others (Fig.
63). They made a straight line very nearly, only the satellite third
from Jupiter was slightly above the line. The fixed star formed with
Jupiter and the most easterly satellite an equilateral triangle, as in
the figure.
March 2: 0 h. 40 m.—Three satellites were in attendance, two on the
east and one on the west, in the configuration shown in the diagram
(Fig. 64). The satellite furthest to the east was 7´ from Jupiter; from
this satellite the next was distant 0´ 30´´, and the satellite on the
west was separated from Jupiter by an interval of 2´. The satellites
furthest off were brighter and larger than the remaining satellite,
which appeared very small. The satellite furthest to the east seemed to
be raised a little towards the north, out of the straight line drawn
through the other satellites and Jupiter.
The fixed star already noticed was at a distance of 8´ from the western
satellite, that is, from the perpendicular drawn from that satellite to
the straight line drawn through all the system, as shown in the figure
given.
These determinations of the motion of Jupiter and the adjacent planets
(his satellites) by reference to a fixed star, I have thought well
to present to the notice of astronomers, in order that any one may
be able to understand from them that the movements of these planets
(Jupiter’s satellites) both in longitude and in latitude agree exactly
with the motions [of Jupiter] which are extracted from tables.
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.
[Sidenote: Deductions from the previous observations concerning the
orbits and periods of Jupiter’s satellites.]
Public-domain text, read in full here on John Shaqi.
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