How to find it
The Great Rift in the Milky Way is easy to see if you have dark skies. However, you aren’t looking for a bright object. You are actually wanting to see the dark lanes running the length of th starlit Milky Way band.
You will be looking south from mid-summer through about October – in a dark sky – and you should see the Milky Way come off the southern to southwestern horizon. Notice that the Milky Way band looks milky white. The skies aren’t really black like ink between stars in the Milky Way. You will know when you see the Great Rift because it is as if someone took a marker and colored it darker.
The Great Rift begins just above the constellation Sagittarius. Follow the Milky Way up until you see a black area in the Milky Way just before you get to the constellation Cygnus, which has the shape of a cross.
Don’t miss the Milky Way and Great Rift Rise
One of the most spectacular sights is to see the Milky Way as it rises. Around 10 p.m. in June, step outside and look in the east to see the phenomena of the Great Rift and the rest of the Milky Way make its dramatic entrance as it rises into the summer skies. Make sure you have your binoculars handy to scan the Milky Way. There are many interesting star forming regions, star clusters and millions of stars that will capture your attention. Look in the Great Rift and imagine all the stars that will eventually reveal themselves as the molecular gas dissipates.
Molecular dust is the reason it is dark
The Great Rift is caused by the star forming regions in that part of our galaxy. The proto-stars (newly forming stars) are generating molecular dust that doesn’t allow light in the visual spectrum to shine through. However, with the advancement of telescopes that see in different light waves – such as X-rays or infrared – we now know that there is activity in the area.
Ancient cultures focused on the dark not the light areas
You know those paintings where if you look at the light areas you see one thing, but in the dark areas you see something else? The dark rift is a bit like that. A few ancient cultures in Central and South America saw the dark areas of the Milky Way as “constellations,” and they had a variety of myths associated with them. Another well-known late-19th and early-20th century U.S. astronomer, E. E. Barnard, also liked to look at the dark regions of the Milky Way.
The other famous area of the sky that is obscured by molecular dust is the famous Coal Sack nebula near the Southern Cross, or constellation Crux. The Coal Sack is another region of star-forming activity in our night sky – much like the Great Rift.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.