The Southern Cross constellation is one of the striking features of the southern hemisphere sky. It is one of the first star patterns that New Zealand children learn to recognise. The 16th-century European navigators who sailed into southern seas perceived it as a symbol of their Christian faith. The Southern Cross is evocative of place or origin to many peoples, appearing on national flags, company logos and memorials in New Zealand and elsewhere in the southern hemisphere.
Depicted either as four or five stars, the Southern Cross features on the national flags of New Zealand, Australia, Brazil, Papua New Guinea and Samoa. It also appears on the Australian flags of Victoria, Australian Capital Territory and Northern Territory, and on the flag of Chile’s Magallanes region. The flag of the Southern Common Market, the South American trading bloc of Argentina, Brazil, Paraguay and Uruguay, also depicts the constellation.
When New Zealand soldiers sailed off to to fight in South Africa at the beginning of the 20th century, they were singing: ‘We are the boys of the Southern Cross, our stars shine on our flags’. Over a century later the constellation continues to be relevant to nationhood and national honour. It is depicted on the New Zealand Tomb of the Unknown Warrior, unveiled in 2004. Featured on the lid of the tomb, the stars are seen to have guided the warrior back to New Zealand from distant battlefields.
It pays to be specific when using the term Southern Cross in New Zealand, for apart from its astronomical association, the name has been used for planes, boats, newspapers, and numerous commercial ventures.
The first aeroplane to cross the Tasman Sea, in September 1928, was the Southern Cross, a three-engine Fokker, flown by Charles Kingsford Smith and C. T. P. Ulm.
A number of ships have been named Southern Cross, but perhaps the most famous was the Shaw Savill passenger liner that brought assisted immigrants from Great Britain to New Zealand in the mid-1950s and 1960s.
Two national newspapers have been published under the name: a successful paper from colonial days, which merged with the New Zealand Herald in 1876; and a short-lived Labour Party daily (1946–51).
Once visible to ancient Greek astronomers, the stars of the Southern Cross disappeared from their view due to the rotating earth wobbling like a top (precessing).
Although the Southern Cross is the smallest of the 88 official constellations, it has achieved prominence from its value as a navigational aid. It is visible throughout the year in southern skies. The four brightest stars form a distinctive cross with a long axis and a short crossbar. A fifth star, located just below the crossbar, is often included in depictions of the constellation. This star is fainter than the others and not always visible. On clear nights, away from city lights, those with good eyesight should be able to see 34 stars in the Southern Cross. A telescope reveals thousands more.
There are different traditional interpretations of the Southern Cross in New Zealand, and it is known by at least eight different names in Māori. Tainui Māori saw it as an anchor, named Te Punga, of a great sky canoe, while to Wairarapa Māori it was Māhutonga – an aperture in Te Ikaroa (the Milky Way) through which storm winds escaped.
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.
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.
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.
Many stars have names that indicate their brightness and location in a particular constellation. Astronomers call the Southern Cross the Crux and attach a letter of the Greek alphabet to the main stars in their order of brightness. The brightest star is at the bottom and, moving clockwise, the main stars are progressively dimmer.
The brightest star is Alpha Crucis, also known as Acrux. It is the 14th brightest star in the sky and is really a triple star. When viewed through binoculars it appears as two blue-white stars. With a good telescope it is possible to discern that the brighter of the two is really another pair. They are located 321 light years from earth.
Beta Crucis, also known as Mimosa, forms the eastern tip of the upright cross. It is the second brightest star in the Southern Cross, and the 20th brightest star in the sky. Lying some 353 light years away, it is a blue-white giant star.
Gamma Crucis or Gacrux, at the top of the cross, is a distinct red-orange star, and stands out in contrast to the other, blue-white stars of the cross. It lies 88 light years from earth.
Delta Crucis is the faintest of the four stars making up the cross. Like Beta Crucis, it is a blue-white giant star. It lies some 364 light years from earth.
The faint fifth star, Epsilon Crucis, shows up as a dusty orange colour below and just to the left of Delta Crucis. It is not represented on the New Zealand flag, and is barely visible from light-polluted cities and suburbs. This star is an orange giant, located about 570 light years away.
Some early visitors to New Zealand were singularly unimpressed with the Southern Cross. Samuel Butler commented, ‘The southern cross is a very great delusion. It isn’t a cross. It is a kite, a kite upside down … with only three respectable stars and one very poor and very much out of place.’ 1
And an 1888 diarist wrote, ‘The Southern Cross … is a fraud, in as much as it is scarcely brighter than … its neighbours.’ 2
The Jewel Box is a cluster of stars beside Beta Crucis that can easily be seen through binoculars. It appears as a single, bright orange-red star set amongst eight blue and white stars. Through a telescope a group of about 50 blue-white stars can be seen. Astronomers classify this grouping as an open cluster – a loose collection of young stars formed at the same time – and list it in the New General Catalogue (a comprehensive list of deep-sky objects) as NGC 4755.
On dark moonless nights it is possible to make out an inky patch of sky just to the east of the Southern Cross, extending from the base of the cross toward Beta Crucis. Known as the Coal Sack, it is a dark nebula – a cloud of gas and dust dense enough to block out much of the light from the stars behind. It is estimated to be 600 light years away.
Ellyard, David. Astronomy of the southern sky. Pymble: Harper Collins, 1993.
Hall, Richard. How to gaze at the southern stars. Wellington: Awa Press, 2004.
Hyde, Vicki. Night skies above New Zealand. Auckland: New Holland, 2003.
Warner, Lionel. Stars and planets of the southern hemisphere. Auckland: Heinemann Reed, 1989.