Stargazing in January: a scintillating sparkling star in the south

Long known as the Dog Star, it’s the leading light of the constellation Canis Major, the Great Dog, which loyally follows the great hunter Orion across the night sky, writes Nigel Henbest

Dazzling Sirius outshines its tiny companion – the ‘Pup’ – 10,000 times over (Nasa/Hubble)

This winter, our skies are spangled with plenty of brilliant lights, headed up by the bright planets Venus, Mars, Jupiter and Saturn. But there’s one that stands out from the others: a scintillating light in the south that sparkles wildly in every colour you can imagine, like a diamond that’s out of control.

This is Sirius, the brightest star in the night sky. Long known as the Dog Star, it’s the leading light of the constellation Canis Major, the Great Dog, which loyally follows the great hunter Orion across the night sky.

If you view it from space, Sirius is a constant pure white beacon against the black of the Cosmos. But when we see it through the turbulent atmosphere above our heads, the light from Sirius is constantly bent and split into different colours by pockets of air at different temperatures and densities, acting as tiny fluctuating prisms. Each instant, the beam of light that reaches our eye can be a different colour of the rainbow, and the star appears to flash red, blue, green or white. All stars scintillate, but only Sirius is bright enough to trigger the colour receptors in our eyes.