Sky and Telescope - June 2018 - 66
Charles Messier was born. Astronomers had been using telescopes for
more than a century, but reﬂecting
telescopes and achromatic refractors were
still decades away from being widespread.
Serious observers used aerial telescopes, tubeless designs in which the objective lens and eyepiece were
separated by dozens or hundreds of feet to reduce chromatic
aberration. Aerial telescopes look cumbersome, but they
were good enough to allow Giovanni Cassini to discover four
moons of Saturn in the late 1600s and the ring gap that bears
his name, the Cassini Division.
Far to the east of Coma, the brilliant double star Albireo
sits at the head of Cygnus, the cosmic Swan, 430 light-years
away. The light we see now left the stars in the late 1500s.
In the last great age of pre-telescopic astronomy, the world
wrestled with the heliocentric cosmology proposed by Copernicus. To challenge the Earth-centered views of Ptolemy was
not only intellectually daring, but also mortally dangerous,
given prevailing religious views. To resolve the question,
Danish astronomer Tycho Brahe measured the courses of the
planets with unprecedented accuracy - data that would allow
J U N E 2 018 * SK Y & TELESCOPE
laws of planCluster
etary motion in
the early 1600s.
the skies more accurately than any before him,
but people all over the world had
been making similar observations for millennia - as our next
few steps will demonstrate. The Antikythera mechanism was
a Greek mechanical computer used to predict astronomical phenomena, from the ﬁrst or second century BC. That's
about the time that the Olmecs, Mayans, and other Meso-