The Great Diamond

May 08, 2020

We’re halfway through Spring. A perfect time to look for what some call the “Great Diamond.”

I’m Matt Pelsor, and this is your Weekend Sky Report.

Sweeping high across the southern sky in the spring are the constellations Leo, Virgo, and Bootes (boh-OH-teez). But if you don’t know those constellations, that’s okay. We’re looking for something bigger.

The Great Diamond is made up of four bright stars, Arcturus in Bootes, Spica in Virgo, Denebola in Leo, and the star Cor Caroli from the small constellation Canes Venatici (CANE-eez vin-AT-uh-sigh). The Great Diamond actually takes up more of the sky than even the Big Dipper. And you can use the Big Dipper to find it.

There’s an old mnemonic device to help you find the two brightest stars, Arcturus and Spica. Using the handle of the Big Dipper, follow the arc of the handle to Arcturus, and then spike across the sky on that same trajectory to the bright star Spica. Arc to Arcturus, and spike to Spica. Then look up and to the right of those two stars to form an almost equilateral triangle with Denebola in the constellation Leo. It’s the second brightest star in Leo behind Regulus. Then, complete the Great Diamond with Cor Caroli above those three--it’s the highest star in the Great Diamond, and if you’re observing around 11:30, it’s practically straight up.

And if you have a telescope, get it out and look at Cor Caroli. Careful observers will notice two stars--it’s a binary.

And if you have a big telescope, you probably already know about the Virgo Cluster, which sits right near the middle of the Great Diamond and consists of over a thousand known galaxies--most of which are too faint for amateur telescopes, but some are bright enough for backyard viewers with lots of aperture.

I’m Matt Pelsor… Happy Skywatching.