I would assume that almost any good book on astronomy would contain a picture 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, Lyra. Although generally considered a summer constellation, Lyra is still very much set to be seen, now more than two weeks into the fall season.
Go outside this week around 10pm local time of day and face the sunrise. About two-thirds of the way up from the horizon, you’ll spot a bright bluish-white star. This is Vega, the brightest star in Lyra. The only other star at that hour that outshines Vega in brightness is yellow-orange Arcturus in the constellation Boötes the Shepherd. But Arcturus will be in the opposite part of the sky, about halfway to the southwest.
The constellation Lyra was supposed to represent Apollo’s harp. Six fainter stars form a small geometric pattern of a parallelogram attached to its northern corner by an equilateral triangle. Vega shines in the western part of the triangle. The two lowest stars in the parallelogram are Beta and Gamma Lyrae. Beta is sometimes known as Sheliak and Gamma also goes by the name Sulafat. Between these two stars, but a little closer to Sulafat is where you’ll 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 getting to grips with your own impressive sky-gazing photography, don’t miss our guide on how to shoot the night sky. We also have recommendations for the best astrophotography cameras and the best astrophotography lenses.
A heavenly curiosity
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 it as a perfectly outlined disk as large as Jupiter, but dull in light and looked like a faded planet.
Some time later, Charles Messier also saw it and added it to his catalog of masquerade comets, listing it as Messier 57, or M57. But like de Pellepoix, Messier’s telescope was too crude to give a true picture of what he was looking at. “It appears to be composed of very small stars,” wrote Messier, adding that, “but with the best telescope it is impossible to distinguish them; they are merely suspected.”
Only six years later, in 1785, Sir William Herschel (discoverer of Uranus) actually saw M57 as a ring. “It is among the curiosities of the heavens; a nebula having a regular concentric dark spot in the middle.” Herschel, however, mistakenly assumed he was looking at “a ring of stars.”
Gas shell or tunnel?
As for the true nature of the ring, it is generally believed that sometime in the distant past, a star nearing the end of its life and having used up all its nuclear fuel ejected large masses of gas into space in a gaseous shell. This surrounding gas is still expanding and is made visible by the glow from its extremely hot central star (which is simply the core left over from the original star). The star’s surface temperature is estimated at 216,000º F (120,000º C). Our Sun is expected to undergo a similar process in a few billion years.
The Ring Nebula is the most famous and among the brightest examples of what astronomers call “planetary” nebulae. But despite their name, planetary nebulae have absolutely nothing to do with planets. This is simply because they generally appear in telescopes not as stellar point sources, but as small diffuse discs.
For a long time, the explanation for the appearance of the Ring Nebula was that the nebulous disk was so much brighter around its edges that it looked like a ring; that we are looking through the edge of the gaseous shell lengthwise. Therefore, there is much more gas in our line of sight, and the refraction of light by the central star makes it brighter because each particle acts as a prism or mirror and reflects the rays back to us.
More recent research, however, has confirmed that it is indeed likely to be a ring, or torus, of luminous material surrounding its central star. In fact, based on pictures taken by the Kitt Peak National Observatory near Tucson, Arizona, some think we can actually see down a gas tunnel shaped like a barrel or cylinder.
See for yourself
As for seeing the ring for yourself, it shines at magnitude +8.8, and is thus too faint to see with the naked eye. Any good pair of binoculars will locate it, although it will appear almost star-like in appearance due to its small apparent diameter. The shape of the ring can begin to become visible to most eyes in small telescopes using 100-power magnification, although at least a 6-inch telescope is recommended to see the ring clearly. With larger instruments and higher magnifications, the ring clearly looks like a “little ghost doughnut.”
You may wonder if the central star is visible inside the “donut hole”. The answer is “yes and no”. The magnitude of this star is approximately +15. This means it is almost 4,000 times fainter than the faintest star you can see with your own 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 12 inches. Even then, you’d need an absolutely dark and clear, pristine night to even have a chance to glimpse it.
Only once, almost half a century ago, in 1975, did I see it. It was the middle of the annual summer Stellafane convention, just outside of Springfield, Vermont. The Ring Nebula was one of the first objects seen through the 12-inch Porter turret telescope atop Breezy Hill. However, I hasten to add that my eyes were much younger then, and the overall level of light pollution in much of New England was significantly less then than it is now.
Bottom line: sure, you shouldn’t have any trouble seeing the Ring Nebula, but its central star will most likely lie out of your reach.
Joe Rao serves as an instructor and guest lecturer in New York Hayden Planetarium. He writes about astronomy for Journal of Natural History, Farmers’ Almanac and other publications.
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Image Source : www.space.com