We asked local astronomer Stephen Mackintosh to write a guest blog about the star Arcturus. Read on for his fascinating insight into the 4th brightest star in the sky and after which we named our very own Torridon gin.
“If you look outside on a clear night at the moment you’ll see two bright objects dazzling in the Southern sky above. Lowest on the horizon is the mighty gas giant Jupiter sitting in the dim constellation Libra. Jupiter is at its brightest and most vibrant phase for observing at the moment having just reached opposition on the 8th May. With a telescope or good set of binoculars you can see its four brightest moons orbiting the planet as tiny points of light. Watch over a period of several hours and you’ll even see them progress in their graceful orbits around the planet.
Meanwhile, above Jupiter and shining with a vibrant orange light is the star Arcturus, 4th brightest in the night sky. Arcturus means ‘bear watcher’ and you can find it very easily by following the stars in the handle of the Big Dipper (or plough). But why the orange colour? The reason is both fascinating and humbling at the same time. Arcturus is a red giant star. Red giants are stars that dramatically expand in size due to a shortage of hydrogen fuel in their cores – in Arcturus’s case it has swollen to over 20 times the size of our sun. Interestingly Arcturus and our Sun started out life with similar sizes and mass, but the key difference between them is that Arcturus is much much older, around 3 billion years older to be precise! In this way looking at Arcturus is like looking at a premonition of the fate that awaits our own Sun in several billion years’ time, when it too begins running out of fuel.
Arcturus will remain in this red giant phase for many millions of years before shedding its outer layers to become a beautiful planetary nebula, like the famous ring nebula we see in the constellation Lyra. After this the star will become a white dwarf, an earth sized ball of dense matter slowly cooling over billions of years. But its final fate is even more amazing. After cooling over uncountable ages it will finally crystalise into a giant Earth sized diamond, sitting forever in the blackness of space. Such is the incredible fate of of stars like our Sun and Arcturus.” – Stephen Mackintosh
Stephen Mackintosh is a local astronomer and mathematician from the Scottish Highlands. He runs Highland Astronomy Tours. Please find details on his website modulouniverse.com