Sidereus Nuncius
Galileo's First Jupiter Observations (4 of 4)
February 15, at the first hour
Galileo is able to separate Io and Europa, but Callisto is lost in Jupiter's glare.
February 15, at about the fifth hour
Galileo loses Io and still can't detect Callisto.
February 15, at the sixth hour
Galileo finally sees Callisto, one little star, exceedingly small,
...toward the west, 2 minutes removed from Jupiter.
February 16, at the sixth hour
February 17, at the first hour
February 18, at the first hour
February 18, at the sixth hour
February 19, at 40 minutes
February 21, at 1 hour 30 minutes
February 25, at 1 hour 30 minutes
February 26, at 30 minutes
A shadow transit of Io, to be followed in short order by transits of Europa and its shadow.
February 26, at the fifth hour
Galileo assumes that Io earlier had been hidden behind Jupiter,
although it and its shadow were actually passing in front of Jupiter during the
first hour after sunset.
Galileo plots a fixed star (not shown here) in order to track Jupiter's
motion. I decided for the first time to observe the progress of Jupiter and
his adjacent planets along the length of the zodiac by reference to some fixed
star, for a fixed star was observed to the east, 11 minutes from the easternmost
planet and displaced somewhat to the south...
This is
HD 32811,
a 7th magnitude star in Taurus located within the triangle formed by 13, 15, and
iota Tauri.
Edmund Halley correctly identified this star in 1720 (On the Method of
determining the Places of the Planets by observing their near Appulses to the
Fixed Stars,
Philosophical Transactions vol. 31, pp. 209-211).
He settled its place in ♊ 13° 24ʹ ½ to the time of the British Catalogue
with 0° 25ʹ south latitude.
In other words, for the 1690.0 epoch and equinox
of the catalog he used, 13° of ecliptic longitude past the zodiac boundary for
Gemini (60°) and 25ʹ south ecliptic latitude, a position within 2 arcminutes of
the modern value for HD 32811.
February 27, at 1 hour 4[0] minutes
February 28, at the first hour
Europa is eclipsed by Jupiter's shadow.
February 28, at the fifth hour
March 1, at 40 minutes
March 2, at 40 minutes
