How to Spot the Southern Cross
This page contains a summary of a chapter from Richard Hall’s excellent How to gaze at the southern stars, which is referenced below.
The Southern Cross was the key for sailors who wished to navigate the oceans of the southern hemisphere, because the North Star, which marks true north, can’t be seen from the waters down under.
To spot the Southern Cross, Te Punga (the anchor), you must first look towards the two pointer stars, which line up in such a way as to point towards the left hand of the cross (if you were to see it as a cross: but remember, the long end will usually be pointing south, so it won’t be oriented like you might expect).
The Acrux, the brightest star of the cross, forms the tip of an arrow pointing south from Te Punga. In that direction, past true south, lies the brightest star in the southern sky: Achernar. The location of the south celestial pole just so happens to be half way between these markers. Throughout the year, these markers will move in the sky; but have no fear! They faithfully circle true south in a clockwise fashion: “like hands on a great clock”.
The last trick is to judge how far north your ship is from the south pole, a measurement known as the latitude. To discern that, all you have to do is measure how far up (angular distance) the south celestial pole is above the horizon. Although European sailors used sextants to measure this, Polynesian sailors knew how to use their hands to judge latitude!
Richard Hall, How to gaze at the southern stars, Awa Press, Wellington, 2004.