Finding south

Since moving to New Zealand, I have come to the firm opinion that the night sky in this part of the world is far superior to that seen in the northern hemisphere.

Ian Griffin
Ian Griffin

The sight of the centre of our galaxy overhead in the middle of winter, or this time of year gazing at the Magellanic Clouds high above the southern horizon as darkness falls, really does fill my heart with joy.

Despite my passion for all things australe, I have to confess that there is one advantage that stargazers in the northern hemisphere have over us. There is a bright star, called Polaris, close to the north celestial pole that makes it easy to find north on any clear night.

The north and south celestial poles are two imaginary points in the sky where the earth's rotation axis, projected outwards, meets the celestial sphere.

The Southern Cross constellation. Photo: Wikimedia Commons
The Southern Cross constellation. Photo: Wikimedia Commons

As Earth rotates, the two celestial poles remain fixed in the sky, and the entire celestial sphere appears to rotate around them, completing one circuit per day.

Here in the south, there isn't a bright star near the south celestial pole. So how can you find it?

As a service to curious pole sleuths, this week's chart shows two ways you can track down the south celestial pole for yourself.

The first method uses the so-called ''pointer stars'' Alpha and Beta Centauri, and the constellation Crux (the Southern Cross), both of which are low in the sky at sunset this week.

To find the pole you need to draw two imaginary lines in the sky. The first line extends up through the long axis of the Southern Cross, while the second line starts from a point halfway along and perpendicular to the line between the pointers. Where these lines cross is very close to the south celestial pole.

If clouds obscure the lower part of the sky, a second way to find the south celestial pole is to use the Magellanic Clouds, which are both high in the sky as darkness falls. Make an equilateral triangle, the third point of which is the south celestial pole.

 

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