We are reaching the end of our countdown of the brightest stars visible from Chicago. SIRIUS is the brightest star in all the night sky (and the brightest star in the constellation of Canis Major, the greater dog). It dominates the winter sky, and its proximity to five other stars on this countdown—Procyon, Betelgeuse, Rigel, Aldebaran, and Pollux—makes those cold nights dazzling.
Sirius is often called the Dog Star, but if it is visible in the winter sky, then where does the phrase, “dog days of summer” come from? There is a connection. In the late spring, Sirius is still visible in the night sky, but it sets earlier and earlier each night. For instance, in May, it sets just after the sun and is barely visible through the bright dusk twilight. By mid-summer, Sirius has completely disappeared behind the glow of the Sun, as it sets (and rises) at nearly the same time. Ancient astronomers reasoned that since Sirius was so bright, it’s light combined with the Sun’s light and made those summer weeks especially hot. By September, Sirius would become visible again in the morning twilight, rising just before the sun.
Of course, Sirius is so far away, just over eight-and-a-half light years, that its light and heat do not add measurably to the Sun’s, but it is still spectacular. In fact, Sirius is one of our closest stellar neighbors—one reason it is so bright.
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