The southern cross
The outstanding star formation and the one simplest to find in our southern skies is, of course, the Southern Cross, known as Crux. Around this constellation will be built our entire study of the southern skies. The Southern Cross can be seen throughout the year from all places at and south of Sydney 's latitude. It is formed by four main stars (Fig. 1).
The Southern Cross has been marked by observers in the Northern Hemisphere in pre-Christian times, and the four main stars were said to represent the four pagan virtues—Justice, Fortitude, Temperance and Prudence. Early Christians naturally accorded it a religious significance, and some of the early emigrants to South America regarded it as a good omen planted before them in the sky as an emblem of their faith.
Like all constellations and other heavenly bodies, the Southern Cross also appears to alter its position in the skies; and observed at the s am e time-say 9 o'clock—each night, throughout the year, this change can be seen quite distinctly (See Fig. 3). In May it stands upright almost overhead to the south, in August it lies further to the west on its side pointing westwards, by November it stands on its head near the horizon and due south, and in February it lies on its side pointing to the east.
Next May it is back to its upright position again high overhead, thus completing a circle in the southern sky. Always the head of the cross points out-wards. Observed at intervals during one night it will be seen to be following the s am e path, describing a circle in the sky like the hour hand of a clock travelling at half speed; but all the stars appear to complete a revolution in about four minutes less than a day. Considered as a twenty-four-Dour clock, then, the Cross gains about four minutes daily, which accounts for its being a little farther on each night round its clockwise circle. With this in mind, it is not difficult to tell the time by the Southern Cross.