Kōrero: Southern Cross

Whārangi 2. Orientation and navigation

Ngā whakaahua

The Pointers

Lying in the Milky Way – the streak of white light that spans the night sky – the Southern Cross can be easily located from its proximity to two very bright stars called the Pointers. They are so named because if you extend an imaginary line connecting the two stars (Alpha and Beta Centauri) it reaches the Southern Cross.

Orientation

The orientation and position of the cross in the sky are constantly changing. It appears to rotate around a point in space known as the South Celestial Pole (it is in fact the earth that is rotating). During the night the orientation of the constellation changes in a regular manner from upright, to lying sideways, to upside-down. Both its position and orientation change over the course of a year. At midnight on 1 April it is upright and high in the sky, but three months later it is lying on its side in the south-west. It will be found upside-down and low in the sky at midnight on 1 October, and at midnight on 1 January it will be lying on its side in the south-east.

Finding south

There is no bright pole star in the southern hemisphere sky that can be used to locate due south in the same way that Polaris indicates north in the northern hemisphere. Instead, there are various ways of locating south by the Southern Cross.

First use the Southern Cross to locate the South Celestial Pole, then drop a vertical line from the South Celestial Pole to the horizon – this marks due south.

Me pēnei te tohu i te whārangi:

Maggy Wassilieff, 'Southern Cross - Orientation and navigation', Te Ara - the Encyclopedia of New Zealand, http://www.TeAra.govt.nz/mi/southern-cross/page-2 (accessed 20 April 2019)

Story by Maggy Wassilieff, published 12 Jun 2006