I imagine that virtually any good book on astronomy would include a photo of what can best be described as the “smoke ring” of the sky. Others may call it a donut or a cosmic bagel, but the popular name for this object is simply the Ring Nebula, located in the constellation Lyra, the Lyra. Although generally considered a summer constellation Lyra, it is still very well positioned for viewing now that the autumn season is more than two weeks into it.
This week, go outside around 10pm local daylight time and look due east. About two-thirds of the way up from the horizon you’ll see a brilliant blue-white star. This is Vega, the brightest star in Lyra. The only other star at that hour that is brighter than Vega is the yellow-orange Arcturus in the constellation Boötes, the Shepherd. But Arcturus is on the other side of the sky, about halfway to the southwest.
The constellation Lyra is said to represent the harp of Apollo. Six fainter stars form a small geometric pattern of a parallelogram attached to an equilateral triangle at the northern corner. Vega shines in the western part of the triangle. The two lowest stars in the parallelogram are Beta and Gamma Lyrae. Beta is also called Sheliac and Gamma is also called Sulafat. Between these two stars, but slightly closer to Sulafat, you will find the Ring Nebula.
Want to see the Ring Nebula or other nebulae for yourself? Be sure to check out our guides to the best binoculars and the best telescopes.
And if you’re interested in your own impressive skywatching photography, don’t miss our guide to photographing the night sky. We also have recommendations for the best cameras for astrophotography and the best lenses for astrophotography.
A heavenly curiosity
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Antoine Darquier de Pellepoix of Toulouse, France, first saw the Ring Nebula in January 1779. Using a telescope with an aperture of about 3 inches, he described the nebula as a perfectly defined disk the size of Jupiter, but dull in the light and resembling a fading planet.
A short time later, Charles Messier also saw it and added it to his catalog of comet masks, listing it as Messier 57, or M57. But like the Pellepoix, Messier’s telescope was too crude to give a true picture of what he saw. “It appears composed of very small stars,” Messier wrote, adding that “but with the best telescope it is impossible to distinguish them; they are only suspected.”
It wasn’t until six years later, in 1785, that Sir William Herschel (the discoverer of Uranus) actually saw M57 as a ring. “It is one of the curiosities of the heavens; a nebula with a regular concentric dark spot in the centre.” However, Herschel incorrectly assumed he was looking at “a ring of stars.”
Gas grenade or tunnel?
As for the true nature of the ring, it is widely believed that sometime in the distant past, a star near the end of its life and having used up all its nuclear fuel ejected large amounts of gas into space in a gaseous shell. This surrounding gas is still expanding and becomes visible through the illumination of its extremely hot central star (which is just the core left of the original star). The star’s surface temperature has been estimated at 216,000º F (120,000º C). Our own sun is expected to undergo a similar process in a few billion years.
The Ring Nebula is the best known and one of the brightest examples of what astronomers call ‘planetary’ nebulae. But despite their name, planetary nebulae have absolutely nothing to do with planets. It is simply because in telescopes they generally do not appear as point sources of stars, but as small diffuse disks.
For a long time, the explanation for the appearance of the Ring Nebula was that the blurry disk was so much brighter at the edges that it looked like a ring; that we are looking through the edge of the gas shell in the longitudinal direction. Therefore, there is much more gas in our line of sight and the refraction of light from the central star makes it brighter, as each particle acts as a prism or mirror, reflecting the rays back to us.
However, more recent research has confirmed that it is indeed likely a ring or torus of bright material surrounding the central star. Based on photos taken from the Kitt Peak National Observatory near Tucson, Arizona, some even think we might be looking at a gas tunnel in the shape of a barrel or cylinder.
See for yourself
As for viewing the ring yourself, it shines at magnitude +8.8, and is thus much too faint to be seen with the unaided eye. Any good pair of binoculars will find it, although it appears almost star-like due to its small apparent diameter. The ring shape can be just barely visible to most eyes in small telescopes with a magnification of 100 power, although a telescope of at least 6 inches is recommended to see the ring clearly. With larger instruments and higher magnifications, the ring appears clearly as a “little ghostly doughnut.”
You might wonder if the central star is visible in the donut hole. The answer is “yes and no.” The magnitude of this star is about +15. That means it is almost 4,000 times fainter than the faintest star you could see with your eyes without any optical aid. And don’t bother looking for the central star unless you have a telescope with an aperture of at least 30 cm. Even then, you would need an absolutely dark and clear, pristine night to catch even a brief glimpse of it.
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Only once, almost half a century ago, in 1975, did I see it. It was during the annual midsummer Stellafan convention, just outside Springfield, Vermont. The Ring Nebula was among the objects visible through the 12-inch Porter telescope atop Breezy Hill. I hasten to add, however, that my eyes were much younger then and the overall level of light pollution in much of New England was considerably lower then than it is today.
In short, you will certainly be able to see the Ring Nebula, but the central star will likely remain out of your reach.
Joe Rao is an instructor and guest lecturer in New York Hayden PlanetariumHe writes about astronomy for magazine Natural Historythe Farmers’ Almanac and other publications.