Growing up in Skibbereen

John Clerke, a man of profound all-round learning, was to his children a painstaking teacher, competent to instruct them in Latin, Greek, mathematics and the sciences. On the practical side, he had a chemistry laboratory in the house where he performed experiments, and a telescope mounted in the garden through which the children were sometimes treated to views of Saturn's rings or Jupiter's satellites.

Astronomy for him was more than a hobby. The four-inch telescope, probably a portable transit instrument, was equipped with a chronograph for timing the transits of stars across the meridian. With this arrangement Clerke was able to provide a time service for the town of Skibbereen, which was as yet unconnected to the outer world by either railway or telegraph.

The principle of timekeeping by the stars is that the astronomer, by referring to a catalogue of star positions, knows the exact instants when these stars cross the southern meridian in the sky each day or night. The time thus recorded is sidereal time, which the astronomer, again by use of the almanac, is able to convert to local mean solar time, in this case Skibbereen time. This in turn could be converted to Dublin time (the standard Irish time, itself 25 minutes behind Greenwich mean time) by allowing for the difference in longitude between the two places.