Looking Up: Into the "Great Rift"

If you're ever fortunate to see the Milky Way stretching across the night sky from a really dark location, you'll see it's not uniformly lit across its length. Here and there you'll see darker regions across its disk. We're looking into one of those regions here, known as the "Great Rift."

This wide field image contains a wealth of detail, and we'll discuss it in the article.

Part of the Great Rift lies in the constellation of the snake, Serpens. This was among the 48 constellations listed by the 2nd century astronomer Ptolemy. This constellation is unique in that it's the only constellation that's split into two totally separate parts. The section where the image above lies is in "Serpens Cauda," literally the serpent's tail. To the west lies "Serpens Caput," or the serpent's head.

Fittingly, the ancient Greeks put "Ophiuchus," the serpent bearer, between them.

While the region contains gas, dust and stars, it's dominated by the dust, which darkens its overall appearance. The Great Rift itself is a giant, dark band which passes through the plane of the Milky Way. The clouds of material which form this feature are known to astronomers as "molecular clouds." The material in them is cold and dense enough for hydrogen molecules to form. These are the necessary building blocks for the creation of new stars.

The thick dust grains gathered in the clouds block off the light from the stars behind them. This creates a mottled appearance with some stars piercing through where the clouds are thinner.

Since we are looking toward the inner part of the galaxy, where there are a lot of molecular clouds, we must recognize that not all of the components we see are at the same distance from us.

Let's try to make our way as best we can into The Great Rift. Inside is an area called the "Serpens-Aquila Rift." This smaller rift spreads across both the Serpens and Aquila constellations and contains the "Serpens Cloud." This is the region shown in our picture. 

Note the bright blue splash of color just to the left of center in the image. This is a reflection nebula known as vdB 123. It's part of a catalog of 158 reflection nebulas assembled by the astronomer, Sydney van den Bergh, who was born in the Netherlands. He put the catalog together from the massive data source of the Palomar Sky Survey. vdB 123 lies about 800 light years away.

Reflection nebulas are blue clouds in space illuminated by nearby bright, blue stars, their light reflecting off the top of the clouds.

Let your eye sweep across the picture to see how many reflection nebulas you can see; vdB 123 is not the only one.There are many fainter ones.

Note also the great river of dark dust in the center of the picture which flows North/South; it's blocking out many of the background stars. These gold colored stars are the ancient citizens which populate the central regions of our galaxy.

Lastly, take a moment to look at the small, orange blob in the center of the image. This is also a reflection nebula, but it's illuminated by reddish colored stars. It's known as the "Serpens Reflection Nebula." It smoulders with a wonderful orange color, like a distant bonfire embedded in the river of dust. This picture might also be titled "Smoke and Fire."

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Wolfe is a member of the Everglades Astronomical Society. Organized in 1981 it serves the Naples community providing information in all aspects of amateur astronomy. Its goals include educating the general public, school children, and other groups to the wonders of the universe. The Society meets at 7PM every 2nd Tuesday of the month at the Norris Center (public invited). Regular viewing visits to a special, dark sky site in the Everglades are held each month, allowing the general public to observe the night sky through telescopes, under pristine conditions. For more information, visithttp://naples.net/~nfn19284/eas/Home.php.