Summer – Orion
In summer Orion becomes prominent in the north-western night sky. Along with the Southern Cross, it is one of the easiest constellations to recognise. People in the southern hemisphere have an upside-down view of what the ancient Greeks recognised as a giant with a sword and belt: New Zealanders see a saucepan. Three bright stars form the base of the pot, and three faint stars its handle. The base of the pot lies along an imaginary line known as the celestial equator: the region above the pot faces south; north is below.
The intense blue star on the handle side of the pot is Rigel. It is the brightest star in Orion, and the seventh brightest in the sky. Classed as a blue supergiant by astronomers, it shines with a light equivalent to 40,000 suns.
Below the pot and diagonally opposite Rigel is Betelgeuse, a distinctive orange-red star. It is the second brightest in Orion and 10th brightest in the sky. A red supergiant, it has a diameter 500 times greater than the sun’s.
Unlike most stars, which burn hydrogen, giants and supergiants have exhausted their hydrogen supply and are starting to burn heavier elements such as helium and carbon. Once these fuels are used up, the giants collapse into their core and trigger a massive explosion known as a supernova.
Winter – the Scorpion
Winter skies are dominated by Scorpius, a long, S-shaped constellation located in the widest and brightest part of the Milky Way. It is best viewed from the southern hemisphere, where it lies overhead in late winter evenings. It needs little imagination to make out the shape of a scorpion. A prominent orange-red star, Antares, represents the heart of the scorpion. One of the largest stars, it is a red supergiant. Just west of Antares, a line of three stars represents the head and claws, and on the other side of Antares, a line curving downwards is the scorpion’s tail.
The Pleiades are an important star cluster also known to stargazers as the Seven Sisters or M 45, and Matariki to Māori. They are a group of young stars that still dwell in the gas and dust of the nebula from which they formed. In New Zealand their first appearance in the wintry dawn sky around late May or early June heralds the Māori New Year.