June 2024


Click for Larger image
News for Norther Colorado and the world

Saturday, June 15, 2024

Sky Tonight—April 2, Follow the arc to Arcturus

Courtesy of EarthSky
A Clear Voice for Science

Visit EarthSky at

Now is a perfect time to look outside in the evening and learn a playful 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 the Herdsman. Arcturus is known in skylore as the Bear Guard.

Arcturus is a giant star with an estimated distance of 37 light-years. It is special because it is 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.

However, 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.

Arcturus, a giant star

Give me five minutes; I’ll give you Saturn

By EarthSky

Astronomy Picture of the Day from NASA/JPL

EarthSky: Space

CHANDRA Photo Album

U.S. Naval Observator Astronomical Information center

Universe Today

StarDate Online

Sky and Telescope

National Geographic

Space Com

Simostronomy Blog

Amazing Space

The York County Astronomical Society

Scope City

James S McDonnell Planetarium

Print This Post Print This Post