The Ring Nebula (M 57)
Planetary Nebula
aka NGC 6720, PNG 063.1+13.9, PK 063+13.1, ARO 9
Integrated Visual Magnitude: 9.7
Apparent Diameter: 1.3'
Mean Surface Brightness: 18.8 mag/arc-sec2
Distance: 2600 ly
 Minimum requirements to view: any telescope under suburban skies

The Ring Nebula is one of the most famous objects in the sky and perhaps the most spectacular example of a planetary nebula.  It is bright, relatively large and most important of all, easy to find midway between two bright stars in Lyra.
Above--the view in a 90mm ETX at 50x with a Meade Super Wide Angle 24.5mm eyepiece.  The field of view (circle) is 79'.  The two bright stars are Sulafat (Gamma, 14 Lyr) and Sheliak (Beta, 10 Lyr).  Note how the position of M57 midway between these stars makes it very easy to find.
The Ring is visible in a 3-inch telescope as an elongated hazy spot.  A 6-inch scope will reveal the famous smoke ring structure.  Many observers describe M57 as having a slight greenish tint.  Users of larger telescopes should try to see the faint central star.  The magnitude of this star is uncertain (perhaps as faint as 14.7 magnitude) and may be variable.  There is some question concerning how large an aperture is required to see it.  Due to the surrounding nebulosity it may be more difficult to see than another star of similar magnitude.  A 14 inch may be required for most observers on a typical night.  I've seen it in my 18 inch with little trouble.  Another difficult but rewarding observation is to see the structure in the fainter central nebula.  With a 16-inch or larger scope look for streaks or streamers.

At the end of an observing session I often like to look up a few old friends such as M57.  After years of observing these favorites no chart is needed to find them.  I am always struck by the combination of size and brightness in the Ring, particularly after spending the evening hunting down other tiny, faint examples of planetary nebulae.  The Ring may not be the largest planetary.  It's not even the brightest.  But it is without question best.

The above image is from the Hubble Space Telescope.  The vivid colors are not visible in the eyepiece at all.  In the photograph they provide an indication of the different types of gases and conditions throughout the nebula.
In the Hubble Space Telescope image blue traces very hot helium gas.  Green represents hot oxygen and red indicates relatively cooler nitrogen.  It first appeared that we were viewing M57 as an irregular, spherical bubble in space about the faint central star.  The bright edges which form the apparent ring were explained as the result of looking through more glowing material at the edges of the shell. Some researchers pointed out as early as 1960 that this might not be the case because the difference of brightness between the inner nebula and outer ring was too great.  In recent years evidence has accumulated that the real shape of the Ring nebula may be a cylinder and we are viewing it from one end.  If viewed from another direction it would probably look very different, perhaps more like the Little Dumbbell nebula (M76).  Note the dark spots that are made by small, dark clouds superimposed on the glowing gas.  Few of these clouds are found in the middle of the nebula, suggesting that the overall structure is truly cylindrical.
Millennium Star Atlas Vol III Chart 1153
Sky Atlas 2000 Chart 8
Uranometria 2000 Vol I Chart 117

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