Favorite Star Patterns

Use the Southern Cross to find due south

Very, very many short white concentric lines in the sky above 8 large radio telescope dishes.
The entire southern sky turns around the south celestial pole, a point in the sky captured here behind the antennas of the Atacama Large Millimeter/submillimeter Array in Chile. In the Northern Hemisphere, the moderately bright star Polaris marks the north celestial pole and direction north. But there’s no bright southern star to mark the south celestial pole. Babak Tafreshi, a Photo Ambassador for the European Southern Observatory, captured this photo in 2012. Read more about this image via ESO.

I didn’t know – and you might not realize if, like me, you live in the Northern Hemisphere – that you can use the constellation of the Southern Cross (which appears on both the Australian and New Zealand flags) to find the south celestial pole and the direction due south. An EarthSky community member, Steve Brown, pointed this sky trick out to us some years ago, and he also provided many links and references to finding south with the Southern Cross, many of which you’ll find in this post. Thank you, Steve!

Here we go … first, if you don’t know it already, meet the Southern Cross.

A man, seen from behind, looking outward over a city toward the labeled Southern Cross stars.
View at EarthSky Community Photos. | Prateek Pandey in Bhopal, India, caught the Southern Cross while at its highest point around midnight (its midnight culmination) on March 6, 2021. In April and May, the Southern Cross reaches its highest point in the sky earlier in the evening. Thank you, Prateek!

You might already know that the south celestial pole is the point in the sky directly above Earth’s southern axis. It’s the point around which the entire southern sky appears to turn.

Imaginary sphere around Earth with celestial poles marked above Earth's poles.
The north and south celestial poles lie above Earth’s north and south poles. Image via OneMinuteAstronomer.com.

The height of the south celestial pole in your sky depends on your latitude. The sky’s north pole has a moderately bright star – the North Star, aka Polaris – approximately marking its location. The sky’s south pole has no such bright star. But, if you’re in the Southern Hemisphere, you can indeed use the Southern Cross – also known as the constellation Crux – to find celestial south. Then you can draw a line downward from celestial south to find the direction due south.

The Australian Broadcasting Corporation (ABC) published the following two illustrations showing how to use the Southern Cross to find the south celestial pole and the direction south:

Diagram of line from Crux to south celestial pole and south on horizon.
Imagine a line joining the 2 stars at the ‘head’ and the ‘foot’ of the cross. Extend the line out another 4 lengths from the foot of the cross to the south celestial pole. Then look straight down from the south celestial pole to the horizon. You’ve found south! Illustration and caption via ABCScience.
Complicated diagram with lines between stars pointing to south celestial pole and south on horizon.
Another slighty trickier, but more accurate, way of finding south is to use the Southern Cross and the pointer stars from the neighboring constellation Centaurus. Draw a line through the 2 stars at the “head” and the “foot” of the cross and extend it to the dark patch of the sky the same way as in the first method (Line 1). Then join a line between the two pointers (Line 2). Find the middle of Line 2 then draw a perpendicular line down toward Line 1 until the lines meet. The point at which lines 1 and 3 intersect is the south celestial pole. From there just look straight down to the horizon and you’ve found south. Illustration and caption via ABCScience.

Prefer to get your information via video? Here are a couple of videos showing the same thing, how to use the Southern Cross to find the south celestial pole and due south:

The Southern Cross isn’t the one route to finding celestial south and the direction due south. There are several others way to find south. If you’re interested, try this Wikipedia page. The illustration below, which I found on Wikimedia Commons, shows how to use the Large and Small Magellanic Clouds to find celestial south.

Happy gazing, southern friends!

Diagram with dotted lines from star crossed near south celestial pole, and Magellanic clouds.
You can also find the South Celestial Pole, and due south, using the famous Large and Small Magellanic Clouds. These “clouds” are actually satellite galaxies orbiting our own larger Milky Way galaxy. If you spot them on a clear, moonless night in the Southern Hemisphere, make an equilateral triangle, the third point of which is the south celestial pole. Image via Michael Millthorn/ Wikimedia Commons.

Bottom line: Illustrations and videos showing how to use the Southern Cross to find the south celestial pole and the direction due south.

April 26, 2017
Favorite Star Patterns

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Deborah Byrd

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