The most brilliant region of the Milky Way comes directly overhead on a winter’s evening. Looking up you will notice that there is a dark, almost black rift running along the centre of the brightest region. Today we know that this dark rift is formed by vast clouds of cosmic dust and gas which blot out the light of the more distant stars. But, in ancient times it was believed to be a hole in the sky where the minion of the goddess Artemis ripped open the heavens as it descended to the earth. This minion was the Scorpion. Thus, the constellation of Scorpius is embedded in this most brilliant region of the Milky Way.
The brightest star in the constellation of Scorpio is Antares. It has a definite red hue. Despite its vast distance of 550 light-years, Antares is one of the brightest stars in our sky. This tells us that we are looking at a giant of a star. Its total energy output is equivalent to 75,900 suns. In saying that, bear in mind that our Sun is bigger and brighter than the majority of stars in the Milky Way galaxy.
The surface of Antares is not as hot as that of our Sun, hence its reddish hue. However, the total amount of radiation emitted is compensated by its enormous size. Antares is a colossal star with a diameter 680 times larger than our Sun. If we were to put Antares where our Sun is, its surface would reach beyond the asteroid belt. The Earth, along with the planets Mercury, Venus and Mars would be inside it!
Antares has a companion star which, due to contrast, appears to be a small greenish star. Well, small only when compared to Antares. The companion is hotter than our Sun and is 2,754 times brighter. The two stars orbit around each other in a period of 1,218 years. The companion can only be seen with a telescope.
Antares is only 15 million years old. I say ‘only’ because for stars this is a very young age. Our Sun for example, is 4,600 million years old. However, baby Antares is highly unstable and is expected to explode as a supernova sometime in the next 10,000 years. When it does it will turn our night sky into broad daylight.
Richard Hall
Stonehenge Aotearoa
Photo credit – Judy Schmidt from Fresh Meadows, NY, USA – Infrared Rho Ophiuchi Complex