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
The followers of the Samian philosophy (for I may use this epithet to
designate the philosophy originated by the Samians, Pythagoras and
Aristarchus) have a strong argument against the apparent immobility
of the earth provided in the phenomena of the moon. For we are taught
by optics that if any one of us was in the moon, to him the moon, his
abode, would seem quite immovable, but our earth and sun and all the
rest of the heavenly bodies movable; for the conclusions of sight are
thus related.
Pena has noticed how astronomers, using the principles of optics, have
by most laborious reasoning removed the Milky Way from the elementary
universe, where Aristotle had placed it, into the highest region of the
ether; but now, by the aid of the telescope lately invented, the very
eyes of astronomers are conducted straight to a thorough survey of the
substance of the Milky Way; and whoever enjoys this sight is compelled
to confess that the Milky Way is nothing else but a mass of extremely
small stars.
Again, up to this time the nature of nebulous stars had been entirely
unknown; but if the telescope be directed to one of such nebulous
balls, as Ptolemy calls them, it again shows, as in the case of the
Milky Way, three or four very bright stars clustered very close
together.
Again, who without this instrument would have believed that the number
of the fixed stars was ten times, or perhaps twenty times, more than
that which is given in Ptolemy’s description of the fixed stars? And
whence, pray, should we seek for conclusive evidence about the end or
boundary of this visible universe, proving that it is actually the
sphere of the fixed stars, and that there is nothing beyond, except
from this very discovery by the telescope of this multitude of fixed
stars, which is, as it were, the vaulting of the mobile universe?
Again, how greatly an astronomer would go wrong in determining the
magnitude of the fixed stars, except he should survey the stars all
over again with a telescope, also may be seen in Galileo’s treatise,
and we will also hereafter produce in proof a letter from a German
astronomer.
Public-domain text, read in full here on John Shaqi.
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