Sun rises at 5:56am
Sun sets at 6:28pm
Moon phase: waning crescent
Moon sets at 5:15pm Saturday
Moon rises at 5:57am Sunday
Young and young-at-heart astronomers often learn a few phrases that help them remember how to spot certain stars. The most used one seems to be “Follow the arc to Arcturus and drive a spike to Spica.” This weekend is a good chance to try out your skills at finding Spica using this method. Why Spica? Well, it’s more than just a bright star in the constellation Virgo. It’s also a steppingstone in the path towards finding the Omega Centaur Globular Cluster. Now, if that is a mouthful, it’s not for nothing. But first let’s find it, and then we will learn the reason why.
Follow the arc to Arcturus: Here’s how to locate the star Arcturus, using the Big Dipper as a guide. Find the Big Dipper in the northern sky, it’s up from dusk to sun-up this month and fairly easy to locate if you have a good view of the northern sky.
Once you locate the Big Dipper; notice 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: follow the arc to Arcturus. Arcturus is the brightest star in the constellation Bootes, the Herdsman. This star is known in sky-lore as the Guardian of the Bear, as it is close to the Big Dipper which is also called Ursa Major (The Large Bear.)
Arcturus is a giant star estimated to be 37 light years from earth. It is very interesting to astronomers because it’s not moving with the general stream of stars in the flat disk of the Milky Way galaxy. Instead, Arcturus is moving vertically through the galaxy’s disk at a tremendous rate of speed … some 93 miles (150 km) per second. Millions of years from now, this star will be lost from the view of any future inhabitants of Earth.
Drive a spike to Spica: Once you’ve followed the curve of the Big Dipper’s handle to the star Arcturus, you’re on your way to finding the star Spica. Just keep extending that same curve across the sky’s dome. This will take you to the bright star Spica in the constellation of Virgo.
Omega Centauri: When Spica is high in the sky, Omega Centauri is, too. When Spica is highest, look for Omega Centauri about 35 degrees directly below it. (For reference, a fist at an arm’s length approximates 10 degrees.)
We in St. Maarten, and other locations well south on the planet have a beautiful way to find this cluster. Just look for the famous Southern Cross, which, officially, is the constellation Crux. We learned about the Southern Cross last weekend. Along the eastern edge of Crux is the dark Coal-sack Nebula. Near the Coal-sack – visible in binoculars – is the Jewel Box, an open star cluster with about 100 members, whose stars are somewhat red, white and blue. If you can locate these objects, you’ll also find Omega Centauri.
Omega Centauri is the largest globular star cluster visible to the eye alone. Globular clusters are large, symmetrically shaped groupings of stars. They are distributed, fairly evenly, around the core of our Milky Way galaxy, but very few are visible to the naked eye.
Seeing Omega Centauri is very special in part because you can see it with your eye alone, assuming you have a dark-enough sky. Like all globular clusters, Omega Centauri is best seen through a telescope, but binoculars are still very good. A beautiful sight: a globe-shaped stellar city, teeming with an estimated 10 million stars!
Thank you for keeping up with the Night Sky articles. If you are out later on in the week, each star rises about four minutes earlier each day than written here, and the moon rises 50 minutes later. Night Sky is researched and compiled by Lisa Davis-Burnett. Earthsky.org is a key resource for information and images. Questions or comments? Email This email address is being protected from spambots. You need JavaScript enabled to view it.
