Here in Aotearoa-New Zealand, the sea surrounds us from all directions, the sky is darker than dark, and the stars are very bright. This hemisphere is a magical water-world in which the night sky reflects and the stars descend all the way to the horizon. Over the ocean, the only signposts of the night are the patterns they make. We call these ASTERISMS (roughly from ‘aster’, Latin for star). These asterisms are dot-to-dot shapes that mean something to us.

Long ago, the asterisms were the same as the constellations—some groupings of stars with meaning. Not everyone would attribute the same meaning to the same stars. Depending on where you lived, the same things could mean a fish, a cross or an anchor. This was the case of the Southern Cross. With the advancement of science and the invention of the telescope, objects were discovered that could not be seen without help from binoculars or telescopes.

Many cultures worldwide have named their own constellations and stars since ancient times. However, once science advanced, stars and deep sky objects were discovered that were invisible to the unaided eye, and a better classification system was needed. Astronomers decided to start by mapping the celestial sphere using the model we use on Earth – countries and regions. Although stars are at different distances from us, from Earth we see them as if they lay flat on a sphere; therefore, we call the sky the celestial sphere.

Universal names were needed, too, so just like plants got their scientific name on top of their traditional name, so did constellations.

One set of stars, the variable stars — which brighten and fade rather than shine steadily, became very popular with observers in the late 1800s and the beginning of the 1900s. To map them, it was easier to assign them an area of the sky in which they reside, so it was essential to agree where one constellation ends and the next begins.

Around the 1930s, the International Astronomical Union (IAU) formally accepted the modern list of 88 constellations and adopted official constellation boundaries covering the entire celestial sphere. Eugène Delporte originally listed the 88 “modern” constellations on behalf of the IAU Commission 3 (Astronomical Notations), in Délimitation scientifique des constellations. (Delporte, 1930) (IAU 2020, Constellations)

The official name for the constellation of the Southern Cross is Crux.

Naming the brightest stars in constellations

While stars have many names, ancient names, modern catalogue names, they can now be referred to by their constellation name. For instance, the brightest star in Crux is Alpha Crucis. By convention, Alpha, Beta, Gamma, etc (and the rest of the letters from the Greek alphabet) mark the stars in the order of their brightness, followed by the genitive form of the constellation, in this case, Crucis, which means ” of Crux” in Latin and Alpha Crucis means Alpha of Crux. For the stars in the Southern Cross, these denominations gave further nicknames for these stars, so Alpha Crucis is also known as Acrux, Beta Crucis is Becrux, Gamma Crucis is Gacrux, but Delta Crucis is still Delta Crucis.

About Asterisms

The modern constellations, which are patches of the sky, like countries on Earth, take their name from the associated asterism’s image. Asterisms are dot-to-dot doodles – the patterns on the celestial firmament.

Some asterisms are very small, like the Pleiades, some stretch across many constellations, like here in New Zealand, the waka of Tama Rereti. The same stars can be part of one or more asterisms in the sky, such as the stars of the Pleiades, which are known here as Matariki in June in the morning when they herald the Māori New Year, and in November they are just the feathers of Te Waka O Tamarereti canoe. The same goes for the Southern Cross, the anchor of the Tama Rereti canoe.

Te Waka O Tamarereti asterism is made of the following constellations: Scorpius, Lupus, Centaurus, Southern Cross, Vela, Carin, Puppis, Lepus, Orion and Taurus.

Read More on the IAU constellations’ official page https://www.iau.org/public/themes/constellations/