The Garnet Star

You may have already read my earlier blog about the colour of stars and how stars that may appear white to the naked eye may actually be rich reds or cool blues when viewed with binoculars or telescopes. I'd also written about some of the more spectacular of those coloured stars, such as the yellow and blue couple in Albireo and the flashing red of the supergiant Beletelgeuse. Last night, I had a look at another red supergiant which has the distinction of not only being one of the largest stars that is visible to the naked eye but is also the reddest of the naked eye stars in the night sky. That star is Mu Cephei or more popularly known as Herschel's Garnet Star.

The star is named after Sir William Herschel, the astronomer who, in 1781, discovered the planet Uranus.  Herschel described Mu Cephei as "of a very fine deep garnet colour and ... a most beautiful object, especially if we look for some time at a white star before we turn our telescope to it, such as a Cephei, which is near at hand."

That Garnet Star is located in the constellation Cepheus and in the still photo I took above, you can see it in the top left hand corner, flanked by the contrastingly white Alpha Cephei - the brightest star in the Cepheus constellation - in the bottom right corner. Although it is one of the largest and most luminous stars in the night sky, it will only appear as a faint star to the naked eye - and it is not likely you'll be able to see its distinctive red colouration with the naked eye. This is because it is very far way - it's distance from the sun is too far to measure with any degreee of certainty but it is estimated to be about 2,400 light years (when compared to, say, that other red supergiant, Betelgeuse, which is 'just' 640 light years away).

Nevertheless, despite its great distance away and its faintness to the naked eye, it is bright and it is huge - at nearly 2000 times the radius of our sun, it's as wide as the radius of Saturn if it were to be plopped by a huge cosmic hand right in the middle of our Solar System. And it is 100,000 times brighter than the Sun - one of the most luminous stars known. Seen through binoculars or a telescope, Herschel's Garnet Star is one of the night sky's loveliest sights. The still photo above does not do justice to the its true brilliance and luminosity, as it actually does look like a glittering red garnet suspended in the blackness of deep space. The video I took below might give you just a glimpse of what you would actually see through an optical device.

Finding the Garnet Star should be relatively easy. Around this time of the year, it should be somewhere to the west-northwest in the northern hemisphere. Face that direction, look for the distinctive 'W' of the Cassiopeia and look for the first relatively bright star south of that constellation. This should be Alpha Cephei. Then look for a distinctive, tight triangle of stars that is formed by Delta, Zeta, and Epsilon Cephei (in the top left part of the photo below). Herschel's Garnet Star should be somewhere between  Alpha Cephei and that triangle.

Actually, Delta Cephei (the star at the apex of that triangle) is even more famous than the Garnet Star. This is because Delta Cephei is one of the few easily-visible variables stars - its magnitude (a measure of 'brightness') changes periodically. The Garnet Star is a variable star too, with its magnitude varying from a bright +3.62 to a faint +5 every 2 to 2.5 years. But Delta Cephei's magnitude varies from +3.5 to +4.3 and back, over an amazingly regular period of 5 days 8 hours 47 minutes and 32 seconds. It is, in fact, so accurate that the star acts like a natural clock - but more about Delta Cephei and the other Cepheids in another of my nocturnal outings!

All photographs on this page  © Sabri Zain 2012.