- Capella is the brightest star in the constellation Auriga and the 6th brightest star in the night sky. Capella is about 42 light years away. Although it appears to be a single star to the eye, Capella is actually a system of four stars arranged in two binary pairs.
- Castor is the second brightest star in the constellation Gemini (despite its other label - alpha Geminorum) and the 23rd brightest star in the sky. Although it looks like a single star Castor can be split with small telescopes into a pair of stars of slightly unequal brightness. Each of those stars is also a binary system. Orbiting those four stars at a greater distance is a binary red-dwarf system. Castor is therefore a system of 6 stars. The distance to Castor is about 50 light-years.
- Pollux is the brightest star in Gemini (despite also being labelled as beta Geminorum) and the 17th brightest in the sky. It is an orange giant star about 34 light-years away. Pollux has at least one planet with about twice the mass of Jupiter orbiting it.
- Procyon is the brightest star in Canis Minor and is the 8th brightest star in the sky. Although it is more luminous than the Sun, Procyon is also bright because it's just over 11 light-years from us. Procyon has a dim white-dwarf companion star orbiting it. The presence of the white-dwarf star makes it unlikely that stable planetary orbits within the habitable zone of Procyon to exist.
- Sirius is the brightest star in the night sky and the leading star of the constellation Canis Major. The name Sirius derives from Greek word meaning "sparkling" or "scorching". For various reasons Sirius is also nicknamed the Dog Star. At just under 9 light-years from us, Sirius is one of our nearest neighbours in the Milky Way. It also has a faint white-dwarf companion which orbits Sirius with a period of about 50 years in a very eccentric orbit.
- Rigel is the brightest star in the constellation Orion (despite the label beta Orionis) and the 7th brightest in the night sky. Appearances are deceptive in this case. If Rigel were as close as the other stars in the Hexagon it would blaze hundreds of times brighter than them! Rigel shines with the luminosity of 120,000 Suns but is almost 900 light-years away. Rigel is actually another star system: a blue-white supergiant star orbited by a binary pair of smaller, fainter main sequence stars. However, the majority of the light comes from Rigel A - the blue-white supergiant.
- Aldebaran is the brightest star in the constellation Taurus and the 14th brightest star in the night sky. It is an orange giant star about 65 light years away. Although it appears to be part of the Hyades star cluster Aldebaran is actually in the foreground and unrelated.
Patrick Moore poularised the star pattern called the Summer Triangle in books and on The Sky at Night from the 1950s on. A less well known asterism for this time of the year is the Winter Hexagon. Here it is!
The mathematical part of my brain says No! Seven stars makes seven sides! That should be Winter Heptagon! But before it gets too carried away about the exact nature of the shape...it's already too well known as a hexagon to change it now. I suppose two of the stars are almost on a straight line. Enough.
It's a huge asterism. The angular distance between the top (Capella) and bottom (Sirius) is around 66 degrees. Capella is almost overhead in the UK during winter evenings, while Sirius is low above the southern horizon.
Here are some factoids about the seven stars of the WInter Hexagon:
Much of the constellation Orion is contained within the Winter Hexagon. Looking at the shape I feel that Betelgeuse should somehow be included - a brightest star inside it but offset from the centre.
Just to put the WInter Hexagon into context - here is a Stellarium rendition of the sky with the familiar constellations in place along with the Hexagon.
Dr Adrian Jannetta
Guitar strummin' explorer of the universe. Mild mannered maths teacher by day and astronomer by night.