Astro Bob A look at celestial happenings in the Northland and beyond Bob King View my profile Click here to view previous posts or additional resources

Keeping an eye on the bear

To find Arcturus, face northeast around 10 o'clock from a location with a good view of the eastern sky. Start with the Big Dipper and follow the bend in the Dipper's handle straight down to Arcturus. Saturn is three outstretched fists to the right and above Arcturus and a magnitude fainter. Created with Stellarium

We touched on winter and summer stars in yesterday's blog but between these extremes lies the transition season of mud and grass fires we call spring in Duluth. Just as winter has Orion, spring has brilliant Arcturus in Bootes the Herdsman. No need to set the alarm to see this one. If you're out around 10-10:30 p.m. and look to the northeast, Arcturus is that flashing red ruby well below the Big Dipper. Just follow the arc of the Dipper's handle down toward the east and you can't miss it. Arcturus is the third brightest star in the sky and "waiting in the wings" low in the northeast. Catch sight of it now and you'll be able to follow its gradual ascent to dominance in the southern sky come May.

Arcturus is an orange giant star 26 times larger than the sun and shines 110 times more brightly. When you find it, consider that the light you see left the star in 1973 which is another way of saying it's 37 light years away. The name Arcturus derives from "arktos" the Greek word for bear (also the root of the word arctic), and indeed Arcturus means the Bear Guard. He keeps watch on Ursa Major the Great Bear (Big Dipper) as the bear paws his way up in the northeastern sky during February and March.

Arcturus is 22.5 million miles in diameter compared to the sun's 864,000 miles. Illustration: Bob King

Once you've found Arcturus, look three fists to the right and above it and you'll bump into the planet Saturn. It's in Virgo and a little higher up in the southeastern sky. Saturn, while bright at first magnitude, is no match for brilliant Arcturus. If you compare the two, you'll notice a key naked eye difference between a planet and a bright star. Stars twinkle and planets generally do not since planets have measurable disks compared to the pointlike stars. Air turbulence affects tiny point sources much more than celestial objects that have distinct dimensions.

Highlights this week include nice pairings of Mars and Saturn with the moon plus the improving visibility of Venus after sunset. Illustration: Bob King

Posted by: rking@duluthnews.com on 2/22/2010 at 11:42 PM | Comments (0) | Permalink | Edit

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