By Donna Vanzetti and Carol Redford
A Bit About the Southern Cross
First, before we discover how to find south using the Southern Cross, let’s learn a bit about this well-known constellation.
When you look up into the night sky, what do you see? Most people simply see an ocean of glittering stars, but with just a small amount of knowledge, you will be able to learn the star patterns of the constellations which reveal a world of ancient stories, spread out across the night sky.
One of the easiest and well-known constellations to find is the Southern Cross. This is the smallest of the 88 constellations and throughout autumn and winter you can find it lying high in the southern sky. And you can even find south using the Southern Cross!
When you head outside to stargaze in the early autumn evenings, you will first notice two bright stars on a diagonal. The brighter of the two and closer to the horizon, has been commonly known as Alpha Centauri, but the International Astronomical Union officially refer to it Rigel Kentaurus from its old Arabic name “foot of the centaur”.
Together, the two stars are commonly known as the “Pointers”, because they seem to point towards the Southern Cross. In early autumn evenings, the Southern Cross itself is above the Pointers. It looks like a diamond lying on its side and is actually made up of five stars.
The Southern Cross is officially what’s known as an asterism, a collection of stars that belong to the constellation of Crux. The International Astronomical Union website is a great place to take a look at all 88 constellations. See if you can find Crux in the list.
How to Find South Using the Southern Cross
Now let’s find south using the Southern Cross.
First, imagine a line extended out from the long axis of the Southern Cross. At the same time imagine another perpendicular line extending from between the Pointers. Roughly, where these two lines intersect, marks our South Celestial Pole. Drop a line straight down to the horizon to find due south!
Major Stars in Crux
All constellations have bright stars that are listed using the Greek Alphabet. Alpha always designates the brightest star in a constellation.
Alpha Crucis or Acrux is the brightest star in the the Southern Cross (or Crux). It’s the 12th brightest star we see in the night sky and is 321 light-years away.
Beta Crucis, also known as Mimosa, is the second brightest star of the Crux constellation and is approximately 350 light years from Earth.
Gamma Crucis or Gacrux is a red giant star and approximately 88 light years from Earth.
Delta Crucis is known as a subgiant star and is about 360 light years away.
Epsilon Crucis – Epsilon is an orange giant and is approximately 228 light years away.
The brighter of the two pointer stars, Rigel Kentaurus, may look like one star with the naked eye, but when you look at it through a medium to large telescope, you’ll see there are two stars. These are called Rigel Kentaurus A & B.
But that not all! Rigel Kentaurus is actually a three-star system with the third star, not visible to the eye, called Proxima Centauri. But it is a notable star as it is our next closest star to Earth after the Sun, at a mere 4.2 light years away.
Significance of the Southern Cross
The Southern Cross is easily visible in the Southern Hemisphere and not visible at all, north of +20° in the northern hemisphere.
It holds special meaning in Australia and New Zealand, where it is circumpolar (continually visible above the horizon) and can be seen throughout the year. Although it does get very low on the horizon depending where you are in. The Southern Cross is represented on the national flags of Australia, New Zealand, Papua New Guinea, Samoa and Brazil.
Crux means “the cross” in Latin and carries cultural significance in many countries in the southern hemisphere.
A stone image of Crux constellation has been found in Machu Picchu in Peru. The Maori called it Te Punga, or “the anchor”. In Australian Aboriginal astronomy, the Coalsack Nebula which is the dark area underneath the Southern Cross in early autumn and winter evenings, represents the head of the Emu in the Sky.
So, enjoy this beautiful constellation, shining so brilliantly overhead in our southern night sky.
Are you inspired by the stars?
Every month, there’s something new to see in WA’s amazing night sky. Head over to Astrotourism WA for a preview of what’s coming up this month.