Spotlight on Sirius

Well, Chicagoans, it’s been another stormy, cloudy, messy week. While waiting for the skies to clear, I’ll highlight Sirius, the brightest star in the night sky (above image from Wikimedia user Mellostorm), about twice as bright as the next brightest star. Because it is so bright, it can be especially twinkly (depending on how turbulent the atmosphere is, of course). It is a bluish-white star, but as it twinkles, you can usually see it flicker into many other colors.

In North America, February is the best month to view Sirius. It rises just before sunset, and thus is visible all night long. After the Moon and Jupiter, it is the brightest object in the sky, so you can’t miss it. Look for it below and to the left of Orion (you can follow Orion’s belt diagonally downward).

What the eye sees as a single star is actually a double star system. The main star (Sirius A) is about twice the mass of our sun, while its companion (Sirius B) is an aging white dwarf about the size of Earth.

Sirius’s nickname is the “Dog Star,” since it is the brightest star of the constellation Canis Major, the Greater Dog. The constellation Canis Minor, the Lesser Dog, is just above and to the left of Canis Major. Its brightest star, Procyon, is easy to see as well; it’s the first bright object you come to as you scan up and to the left of Sirius.

The phrase “the dog days of summer” comes from the star Sirius. You may be wondering why summer is associated with the dog star when it is prominent in the February sky. Well, the Ancient Greeks believed that when Sirius was visible near the Sun at dawn, that its light would combine with the light of the sun to cause even hotter temperatures. The first day that you can spot Sirius in the east before the sun rises occurs in early August, hence the phrase.

Look for Sirius when the skies clear.

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