Tonight is Jul 29, 2010
Courtesy U.S. Naval Observatory
It’s now the perfect time to look outside in the evening and learn a phrase useful to skywatchers. Scouts learn it. Grandparents teach it to kids. It was one of the first sky tools I learned to use in astronomy.
The phrase is: follow the arc to Arcturus.
First locate the Big Dipper asterism in the northeastern sky in mid-evening, maybe around 9 p.m. Can’t find the Big Dipper? Look ahead to our chart for April 6.
Once you can see the Big Dipper, notice that it has two parts: a bowl and a handle. Then – with your mind’s eye – draw an imaginary line following the curve in the Dipper’s handle until you come to a bright orange star. This star is Arcturus in the constellation Bootes, known in skylore as the Bear Guard.
Arcturus is a giant star with an estimated distance of 37 light-years. It’s special because it’s not moving with the general stream of stars, in the flat disk of the Milky Way galaxy. Instead, Arcturus is cutting perpendicularly through the galaxy’s disk at a tremendous rate of speed . . . some 150 kilometers per second. Millions of years from now this star will be lost from the view of any future inhabitants of Earth, or at least those who are earthbound and looking with the eye alone.
But for now Arcturus is one of the easiest stars to find, using the Big Dipper as a guide. Try it, on a lovely spring evening soon.
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what time will it appear
At 12:30AM
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Saturn was pretty cool to see ,
Follow the arc to Arcturus — and speed to Spica! That is, if you continue the line of the arc past Arcturus, you’ll come to another star, Spica, which is not as bright and which is in the constellation Libra, the Scales. The Scales are hard for me to spot, but Spica is pretty easy.
@ Kris
Spica is the alpha star in the Zodiac constellation of Virgo, not Libra.
But you’re right, follow an imaginary curving path will take you from Alkaid (handle end of Big Dipper) to Arcturus (junction of Bootes) to Spica (mid-bottom section of Virgo). I call it the “Spring Arc.”