The Galactic Dark Horse Rides Again!

A view looking south down the Milky Way where it passes through the zodiac constellations Scorpius and Sagittarius around 11:30 p.m. in mid-late June. The Dark Horse sticks out from the main dark band to the right of center. See diagram below for help. Credit: Eric Hines

Giddyup! Time to gambol down the Great Rift of the Milky Way in search of the Galactic Dark Horse. He’s one of many ‘dark constellations’ we might fashion from the ebony clouds of interstellar dust that pool along the band of the Milky Way.

This key will you identify the parts of the Galactic Dark Horse. Credit: Eric Hines

In late June, the Milky Way begins its rise across the eastern sky at nightfall. From the suburban fringes and countryside, you’ll have no problem seeing the soft band of hazy light that first-time observers often mistake for approaching clouds. Even a casual inspection will show that the band is not evenly-textured. In particular, there’s a large gap or split extending from the Northern Cross all the way down to Sagittarius in the south. Astronomers call it the Great Rift.

The Rift splits the Milky Way down the middle and runs all the way from the Northern Cross (Cygnus) through Sagittarius in the south. It consists of enormous clouds of interstellar dust and gas in the plane of the galaxy called dark nebulae that blot out the more distant stars. If you could suck it all up with a monster vacuum cleaner and expose the billions of stars otherwise hidden, the Milky Way would be bright enough to cast shadows.

The Great Rift appears to cleave the band of the Milky Way in two. It’s really cosmic spewed by aging stars and supernovae that accumulates in the plane of the galaxy over billions of years. This view shows the Milky Way from the Northern Cross (left) to Sagittarius at lower right. Credit: Bob King

Tiny dust particles spewed by older, evolved stars and exploding stars called supernovas settle in the plane of the galaxy. Over the eons, it gets re-compressed into new stars. While the dust is really sparse, it adds up over the light years to form a thick, dark band that appears to slice the Milky Way right in half.

A lovely closeup of the dark horse dust clouds silhouetted against the rich backdrop of stars in the Milky Way. The bottom section is the Pipe Nebula. Credit: David Haworth

Australian aboriginal peoples created dark constellations like the Emu by connecting a dark patches of the southern Milky Way into creature forms. One of the my favorite such dark patterns and what’s come to be known as the Galactic Dark Horse (GDH) lies about one outstretched fist to the left of the Scorpius’ brightest star Antares.

Astronomers catalog a number of individual dark nebulae that together form the horse. But to the human brain, which has a knack for seeing patterns in just about everything, the silhouetted outline of a horse prancing on its hind legs is unmistakable. The largest part of the, the hind leg, is also nicknamed the Pipe Nebula and lies 600-700 light years away.

Look about one outstretched fist to the left of bright Antares in Scorpius to spot the Dark Horse. This map shows the sky in mid-June facing south around 11:30 p.m. The horse, specially highlighted here, is a fairly large  feature – about 10 degrees tall.  Stellarium

For skywatchers at mid-northern latitudes, the GDH is best viewed under dark rural skies where the horse prances low in the south not far from Antares in Scorpius. Allow your eyes time to fully dark adapt and look for his dark rump, wispy head and prong-like legs. This is a fairly large but very dim naked eye object some 10 by 7 degrees across. Averted vision will be your friend. Wide-field binoculars will show it in greater detail against a fabulously rich star field. Best viewing during the current moon-free window starts tonight and continues through about July 3.

If we could see the Milky Way galaxy edge-on from afar, it would look similar to NGC 891 in Andromeda. Both have long bands of interstellar dust along their equators that appear dark against the bright starry backdrop. Credit: Jim Misti

Many spiral galaxies like the Milky Way have dark clouds of interstellar dust striping their galactic equators. NGC 891 is just one example. Think of all the wild horses that must be out there!

4 Responses

  1. David E Burson

    Great article, Astro Bob! Thank you! Question: is the Great Rift and Dark Horse still visible in mid to late October? We’re going camping in West Texas and I’d like to point these out to my son. Thank you again.

    1. astrobob

      Hi David,
      The Great Rift is very easy to see in October and November, too. The Dark Horse – at least for observers at mid-northern latitudes – is now getting too low for a good look.

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