THE BIG SKY
SEVEN BRIGHT STARS in the shape of a long-handled saucepan sit over the northern horizon mid-evening this October. It’s a constellation you might already know by one of many names. The Plough, the Big Dipper, the Great Bear – different tags for the same familiar grouping of distant suns, which between them hold a secret.
Train your eyes on the middle star in that line of three forming the pan’s handle. How many points of light do you see there? One or two? The eagle-eyed among you might see a fainter star nestled above the brighter one. Binoculars reveal the pairing nicely, but get a small telescope on them and you’ll find that the brighter one itself splits out into two white stars to make a visual triple star system known as Alcor and Mizar.
But that’s not the real secret. Hidden in the glare of each star is a smaller companion star. Each companion orbits so close to the parent star as to render them invisible to the eye in all but the largest of professional telescopes. It makes Alcor and Mizar a sextuplet star system – and one that soon could be announced as harbouring its own planets!
Look north from your boat on a clear evening and you’ll find the Plough. Image by Jeff Horne.