These are now the dog days of summer, when the weather is supposed to be hot and steamy, with hardly a wisp of wind to stir the stagnant air. According to ancient peoples, the dog days fall between July 3 and August 11 and are named after Sirius, the Dog Star, in the constellation Canis Major, the Greater Dog.
This is the time of year when Sirius rises with the Sun in the daytime sky. The Romans believed that dies caniculares, the dog days, were the time for heat, lethargy and disease, and, for good measure, the naturalist Pliny added that there was also a greater risk of rabid dogs.
The Ancient Egyptians, though, were far more pleased to see the dog days, which heralded the Nile floods, when the river waters irrigated and fertilised parched fields.
The British also took the dog days seriously. The Husbandman’s Practice, published in 1729, offered interesting advice for men to survive the dog days: “Abstain all this time from woman” and “take heed of feeding violently”.
And Sirius may partly explain the folklore legend of St Swithin’s on July 15, because the star rises and sets with the Sun over 40 days — the same number of days as the folklore forecasts for rain or dry weather over high summer.
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Sirius is our brightest star. “The kingly brilliance of Sirius pierced the eye with a steely glitter,” wrote Thomas Hardy in Far from the Madding Crowd. It is also one of our closest stars, despite being about 80 trillion km (50 trillion miles) from Earth.
And Sirius is an impressive star in its own right, about 20 times brighter than our Sun and burning at 10,000C (18,000F) on its surface. And because it is so bright, the Romans assumed that Sirius boosted the summer sunshine and made July and August unbearably hot.
But by no stretch of the imagination can the starlight of Sirius have any effect on the Earth’s climate. Even if the light from all the stars in the night sky were added together it would still be far too weak to make any impact.