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. 20: 1 h. 15 m.—A similar arrangement was seen (Fig. 15). There
were three satellites, so small as scarcely to be distinguishable;
their distances from Jupiter, and from one another, were not more
than 1´. I was doubtful whether on the western side there were two
satellites or three. About the sixth hour they were grouped in this way
(Fig. 16). The eastern satellite was twice as far away from Jupiter as
before, that is 2´; on the western side, the satellite in the middle
was distant from Jupiter 0´ 40´´, and from the satellite still further
to the west 0´ 20´´; at length, at the seventh hour, three satellites
were seen on the western side (Fig. 17). The satellite nearest to
Jupiter was distant from the planet 0´ 20´´; between this one and the
satellite furthest to the west there was an interval of 40´´, but
between these another satellite was in view slightly southward of them,
and not more than 10´´ off the most westerly satellite.
Jan. 21: 0 h. 30 m.—There were three satellites on the east side; the
satellites and Jupiter were at equal distances apart (Fig. 18). The
intervals were by estimation 50´´ each. There was also one satellite
on the west, distant 4´ from Jupiter. The satellite on the east side
nearest to Jupiter was the least of all.
Jan. 22: 2 h.—The grouping of the satellites was similar (Fig. 19).
There was an interval of 5´ from the satellite on the east to Jupiter;
from Jupiter to the satellite furthest to the west 7´. The two interior
satellites on the western side were 0´ 40´´ apart, and the satellite
nearer to Jupiter was 1´ from the planet. The inner satellites were
smaller than the outer ones, but they were situated all in the same
straight line, along the ecliptic, except that the middle of the
three western satellites was slightly to the south of it, but at the
sixth hour of the night they appeared in this position (Fig. 20). The
satellite on the east was very small, at a distance from Jupiter of 5´
as before; but the three satellites on the west were separated by equal
distances from Jupiter and from each other; and the intervals were
nearly 1´ 20´´ each. The satellite nearest Jupiter appeared smaller
than the other two on the same side, but they all appeared arranged
exactly in the same straight line.
Jan. 23, at 0 h. 40 m. after sunset, the grouping of the satellites
was nearly after this fashion (Fig. 21). There were three satellites
with Jupiter in a straight line along the ecliptic, as they always
have been; two were on the east of the planet, one on the west; the
satellite furthest to the east was 7´ from the next one, and this
satellite 2´ 40´´ from Jupiter; Jupiter was 3´ 20´´ from the satellite
on the west; and they were all of nearly the same size. But at the
fifth hour the two satellites which had been previously near Jupiter
were no longer visible, being, as I suppose, hidden behind Jupiter, and
the appearance presented was such as this (Fig. 22).
Public-domain text, read in full here on John Shaqi.
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