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Starwatch: get to know the Great Diamond asterism

Starwatch: get to know the Great Diamond asterism

Beyond the traditional constellations, asterisms can provide a useful alternative way to find your way around the night sky. This week we take a look at one that spans four northern spring constellations.

The chart shows the view looking south-west from London at about 23.00 BST this week.

The Great Diamond is composed of four stars: Arcturus in Boötes, the herdsman; Cor Caroli in Canes Venatici, the hunting dogs; Denebola in Leo, the lion; and Spica in Virgo, the virgin.

All of these stars are the brightest in their respective constellations apart from Denebola, which is outshone by Regulus in Leo. Arcturus and Spica are so-called first magnitude stars, meaning that they are among the brightest in the entire night sky. Arcturus, for example, is the fourth brightest star, and Spica is 15th in the list.

There is also a beautiful colour difference to notice between these two: Arcturus is a deep orange whereas Spica is brilliant blue-white. Continue to follow the asterism anti-clockwise and the stars progressively drop in brightness, with Denebola and then Cor Caroli both being second magnitude objects.

The asterism is also easily visible from the southern hemisphere, spanning the north to north-eastern quadrant of the sky.

Source: theguardian.com