Papers of John Guy Porter

A copy of Porter's script for 'The Night Sky in April' on Jupiter at opposition on 17 April near Spica in Virgo, south of the equator; the moons of Jupiter (the four Galilean moons and the eight discovered since Galileo's time), grouped into three parts: the first group comprised of five regular inner satellites (like Saturn's), the second group containing three moons orbiting in eccentric paths, and the final group orbiting in a retrograde fashion; Melotte's discovery of one of these moons from Greenwich, the large perturbations in its orbit, the likelihood of the capture of these moons by Jupiter and the possibility that there was once a break-up of two captures giving two groups; the different types of satellite found in the solar system, the case of Neptune (in opposition this month near Jupiter), Triton's retrograde orbit and Nereid's eccentric orbit; and the new interest in orbital work aroused by artificial satellites leading to attempts to produce an orbital theory for the outer moons of Jupiter, this made possible by modern electronic calculating machines.

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