The Winter Triangle is an asterism, a shape made up by joining stars which isn't a recognised constellation. The stars Sirius, Procyon and Betelgeuse form the Northern Hemisphere's Winter Triangle (the Southern Hemisphere's Summer Triangle).
The Winter Triangle is very easy to locate by naked eye, you don't need any optical aids. Find Betelgeuse on Orion's shoulder, then follow a direction down from Orion's Belt and you will be looking at sparkling Sirius. Now trace a 'V' upwards for the last component, Procyon, then take the eye-line back to Betelgeuse to complete the triangle.
Though these stars form a triangle shape as we view them from Earth, this is a 2-D perspective. If we could board a space rocket and travel towards each of them at the speed of light, we would reach two of them within 12 years, but the other would still be over 450 years away!
Even a novice stargazer can point out Betelgeuse (alpha Orionis) on the shoulder of the magnificent constellation Orion 'the Hunter'. This red supergiant is a really famous star; after all, almost everyone on this website knows that the characters Ford Prefect and Zaphod Beeblebrox from The Hitchhiker's Guide to the Galaxy originally hailed from the vicinity of Betelgeuse, don't they?
Alpha Orionis is actually a multiple star system; the nearest two companions of Betelgeuse, one at a distance of 5AU1 and the other somewhere around 42AU, were detected by speckle interferometry, which is an imaging technique involving lasers.
Betelgeuse was the first star to have its surface directly imaged by the Hubble Space Telescope in 1996. Now at the end of its stellar life cycle, Betelgeuse is so big that it will eventually go supernova. The massive explosion will, of course, be visible from Earth, even during the day! The death of Betelgeuse will provide celestial fireworks on a cosmic scale, possibly lasting for months. Hopefully there will be human witnesses to record it, just like there were when the star which created the Crab Nebula (M1 in Taurus) exploded in 1054 AD2.
According to Sir Patrick Moore, one of his pet hates is when anyone incorrectly pronounces the name of the brightest star of the constellation of Orion. He likes to mention Betelgeuse a few times a year on his TV programme The Sky At Night, just to remind everyone how it's supposed to be pronounced. Remember, it's bet-el-gerz - not 'beetle-juice'.
Sirius, alpha Canis Majoris, known as the 'Dog Star', is a binary system comprising a white main sequence star, Sirius A, and a dim white dwarf star, Sirius B. Nicknamed 'The Pup', Sirius B was the first white dwarf to be discovered and orbits the main component with a period of 50 years. Sirius B is comparative to the Earth in size, 12,000km diameter but with an equivalent mass of our Sun. This means that if a 12 stone (170lb) earthling could land on Sirius B, he would weigh over 20,000 tonnes.
The apparent magnitude when viewing the system is −1.43 but that's variable. It's so bright because of its nearness to us, the measurement of 8.58 light years3 distance makes Sirius the 5th-closest star to our Sun.
The ancient Egyptians used the pre-dawn rising of Sirius to predict the flooding of the River Nile, which they called akhet (the inundation). This was essential to all life in Egypt; they even had a special god assigned to oversee this action.
Sirius was also revered by the Babylonian culture, and ancient mariners set their sails by it. There's an intriguing mystery surrounding the Dogon tribe, extra-terrestrial visitors and this star, which has its own h2g2 Entry.
Shining well up in the south-east by 8pm is the yellow-white main sequence subgiant star Procyon A, the 8th-brightest star in the sky, in the constellation Canis Minor, the Little Dog. Procyon is Greek meaning 'Before the Dog' — because Procyon rises just prior to Sirius, the Dog Star. Procyon has seven times the luminosity of our Sun, and is double the size, one of the largest stars within 20 light years of us. From our vantage point, Procyon gleams a rich cream colour, shining so brightly because it lies at a close distance of 11.4 light years. Procyon has entered the final process of its evolution by converting its remaining hydrogen into helium. When all the hydrogen is used up, it will shrink to a white dwarf star as it's too small to go supernova.
Canis Minor alpha2 (Procyon B) is a white dwarf companion to Procyon, in size it's just over half our Sun's mass. It was detected by Arthur von Auswers in 1840; even though it couldn't be seen, it was suspected due to the optical irregularities of the main component. It was first visually recorded by John M Schaeberle in 1896. Procyon B lies around 15AU from its interstellar companion.
|α Ori||alpha Orionis||Betelgeuse||+0.4||470||Red supergiant|
|α CMa||alpha Canis Majoris||Sirius 'the Dog Star'||-1.43||8.58||White main sequence|
|α CMi||alpha Canis Minoris||Procyon A 'Before the Dog'||+0.3||11.4||Yellow-white subgiant|