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The brightest star in the night sky has played a key role in the calendars of many cultures. In ancient Egypt, for example, its first appearance in the dawn sky marked the beginning of a new year, and heralded the annual flooding of the Nile. And in Greece and Rome, that dawn showing ushered in the dog days — the most sweltering time of year. It’s a phrase we still use today.
When the phrase was coined, Sirius first rose into view around the end of June — at the start of summer and a long run of hot, humid days. Sirius is the brightest star of the constellation Canis Major, the big dog. So it’s known as the Dog Star. People associated the star with the climate, so they called that time of year the dog days.
Thanks to an effect known as precession, though, the stars gradually shift position relative to the Sun. So now, Sirius doesn’t peek into view in the dawn sky until August. From the southern states of the U.S., it’s been in view for a few days now, while it’s just emerging from the Sun’s glare from more northerly latitudes. It’s in the east-southeast, almost directly below the line of stars that marks Orion’s Belt.
That shift in Sirius’s position has changed the way we think of the dog days. In early times, the phrase referred to a specific time of year — generally from early July to about mid-August. Today, though, it usually refers simply to the hottest period of the year — the dog days of summer.
Tomorrow: A cloud comes crashing down.
Script by Damond Benningfield