Sirius is the brightest star in the night sky, perched on the nose of the constellation Canis Major, the Big Dog. Because of that Sirius is called the “Dog Star.”
It dominates the winter sky as part of what I call “Orion’s Gang” of bright constellations. In Greek and Roman mythology Canis Major is Orion the Hunter’s best hunting dog.
Sirius is also known as the star of winter, but now that we’re more than halfway through spring the Dog Star has left the evening skies, not to be seen again in the early evening until sometime next November.
The very bright star Arcturus, the second-brightest star in the night sky, rules late spring and summer skies. It’s close to Sirius in brightness. I call it the star of summer, and it’s easy to see. Just look for the brightest star in the high southern heavens.
Just to make sure that you’re indeed gazing at Arcturus, use the nearby Big Dipper that’s now hanging upside down in the high northern sky. Follow the curve or arc of the handle of the Big Dipper to the end, and you’ll run right into Arcturus. Just remember the adage: “Arc to Arcturus.”
Arcturus is a Greek name that translates to English as “guardian of the bear.” That’s a little contradictory because Arcturus is the brightest star of the constellation Bootes the hunting farmer who, according mythology, is hunting the Big Bear constellation, or Ursa Major.
The Big Dipper outlines the rearend and tail of the Big Bear and is the brightest part of Ursa Major. Bootes looks much like a giant kite with Arcturus at the tail of the kite.
You may think you’re looking at Mars because of its bright orange hue. Mars is also in the night sky right now, but much lower in the southwestern sky near the constellation Leo the Lion.
You can call up the complete May Star Map on my lynchandthestars.com website to find Mars. Every two years Mars rivals or overtakes Arcturus in brightness as Earth and the Red Planet swing close to each other.
Arcturus is running out of hydrogen fuel in its nuclear core, and the reddish-orange hue is caused by the cooling off as it expands. Arcturus is still 7,300 degrees at its outer layer. Our sun by comparison is just over 10,000 degrees.
Arcturus is more than 25 times the sun’s diameter with a girth of more than 22 million miles. Arcturus’ brightness is mainly due to its proximity to our sun and solar system. It’s about 215 trillion miles away and, believe it or not, that’s close for a star.
It hasn’t always been that close. Arcturus is a very fast traveler in the Milky Way Galaxy. It was Sir Edmund Halley (Halley’s comet) who detected changes in Arcturus’ position by comparing ancient star charts with what he was observing in his time. Since then it’s been determined that Arcturus has been racing toward our solar system at more than 90 miles a second.
Arcturus is cruising along so fast that it changes its position among the stars one full moon width every 10 centuries. It’s thought by many astronomers that as a little as a half a million years ago Arcturus wasn’t even visible.
At 37 light-years away it’s about as close as it’s going get to us. As a matter of fact in about another 500 million years it will fade into oblivion.
Celestial huggings this week: The waxing moon in our evening sky will pass close by three planets this week as it migrates eastwardly at 13 degrees every 24 hours. Tonight, you’ll see a thin crescent moon just to the upper left of Venus in the low western sky. On Wednesday night it’ll pass below Mars in the southwestern evening sky. By Saturday it will slip a little below Saturn, higher up in the southwest sky.
Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores and at his Web site www.lynchandthestars.com.
The Everett Astronomical Society welcomes new members. Go to www.everettastro.org/.
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