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Astronomical Observatory: Cool Images

Images: Ring Nebula in Lyra

Ring Nebula in Lyra Contents: This colorful loop is known as the Ring Nebula (also M57, being the 57th object listed in Messier's famous catalog.) It is estimated to be 1000 to 2000 light-years distant, so that the linear size of the 1.7 arcminute loop we see is almost 1000 times that of the orbit of Neptune. It was first observed in 1779 (by Antoine Darquier de Pellepoix), and appears to the eye as a ghostly grey disk in a moderate-sized telescope. (The vivid colors are lost on the eye because of the low brightness.)

What do we see? A doughnut-shaped region of thin gas is irradiated by ultraviolet light from a central star and fluoresces in multiple colors according to the types of atoms involved: helium atoms emit blue light, once-ionized nitrogen red, and twice-ionized oxygen green. The colors separate depending on how deeply into the nebula the starlight can penetrate. The central star, magnitude 15, emits thermal rather than fluorescent light; its distinctly blue color indicates a high surface temperature (near 20,000 degrees Kelvin). We view the Ring Nebula from an angle about 45 degrees off the central axis of the doughnut.

Why is it shaped that way? Throughout their lifetimes, a slow-moving wind of gas emanates from the surface of most stars, especially in the equatorial plane. As they run out of hydrogen fuel, the speed of outflow can greatly increase. In the Ring Nebula, this second wind is compresses the material from the earlier wind into the doughnut shape, and moves out to form bubbles above and below the doughnut. The latter bubbles can be seen in longer exposures as faint outer loops or rings.

For more on the story of the shape of the Ring Nebula, check out the following in your local library: "What is the Real Shape of the Ring Nebula?" by Sun Kwok, Sky and Telescope magazine, July 2000, pp. 32-37.

Processing: This image was made by Andrew Vanden Heuvel in Astr384 in Spring 2004 using the Calvin-Rehoboth robotic telescope with about 4 hours total exposure time in three filters (follow the link for data and processing details). This image is an improvement over an image made by Phil Ammar in September 2001 under Grand Rapids sky conditions and 20 minutes total exposure time, which was in turn an improvement over an image made 28 April 2001 with less than 2 minutes of exposure time.

Orientation and scale: North is up and East is to the left. The angular dimensions are roughly 4 by 4 arcminutes.

The Ring Nebula is found in the constellation of Lyra, which in turn is dominated by the bright star Vega. Vega, Deneb in Cynus, and Altair in Aquila make up the summer triangle, a large triangle of bright stars that dominate the early evening sky in northern hemisphere summers. The triangle is just as observable in the spring, only at a later hour. The celestial coordinates of the Ring Nebula are 18h53m36s,+33deg2' (epoch 2000).

Content updated 4/28/05



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