This week, shortly after sunset look west for the orange star Arcturus hanging low in the sky. It is by far the brightest star in the constellation of Boötes, the ploughman. The chart shows its position at 19:30 BST on 8 October 2018.
Arcturus is a glimpse of what will happen to the sun in the future. Both stars contain similar amounts of gas but Arcturus is considerably older at around 7 billion years.
The star has used all of its central stock of hydrogen fuel and is now generating energy in a shell around the core. This has expanded the star to around 25 times the diameter of the sun, and lowered the temperature of its outer layers to around 4,000C. The temperature makes the star glow red and not yellow like the sun, which has a surface temperature of 5,500C. Being so large, Arcturus gives out around 170 times more light than our own star.
Arcturus can be located by following the curve of the stars in the handle of the Plough, the well-known northern star pattern that forms part of the constellation Ursa Major, the great bear.
