It's July, it's hot, and it's not hard to see why: the Sun soars high across northern-hemisphere skies, and it's in view for a long time.
People in parts of the ancient world, though, blamed summer's oppressive heat on something we can't see right now: Sirius, the Dog Star. In fact, they described this time of year as the Dog Days -- a label that's still in use today.
Sirius is the brightest star in the night sky. It puts on its best showing during winter. It disappears in the twilight during late spring, and returns to view in August.
But thousands of years ago, Sirius disappeared and reappeared a little earlier. From ancient Greece and Rome, it put in its first morning appearance by early July -- just as the weather was reaching its hottest. So it seemed logical that Sirius was the cause -- its light and heat added to the Sun's to bring things to a simmer.
That's not the case, though -- Sirius is more than eight light-years away, so we feel none of its heat.
Another part of the Sirius legend had a more solid scientific basis, though. People believed that if Sirius looked clear and white when it first appeared in the dawn sky, they could expect a mild, healthy season. But if it looked murky and red, then greater heat, disease, and famine were on the way. And there's some truth to that. Clear, bright skies are less humid and stagnant, so they're not as oppressive -- even during the Dog Days of summer.
More about Sirius tomorrow.
Script by Damond Benningfield, Copyright 2008
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
[1]
