M27 on 2008-09-30


TELESCOPE = 17.5 inch f4.5
OBSERVER = Rusty Fletcher 
LOCATION = Seguin Outdoor Learning Center 
DATE (Yr-Mo-Dy) = 2004-04-01
TIME (UT) = 10:59:25

Planetary Nebula M27 (NGC 6853) 

The Dumbbell Nebula M27 was the first planetary nebula ever discovered. On July 12, 1764, Charles Messier discovered this new and fascinating class of objects. We happen to see this one approximately from its equatorial plane. From near one pole, it would probably have the shape of a ring, and perhaps look like we view the Ring Nebula M57. 

This planetary nebula is certainly the most impressive object of its kind in the sky, as the angular diameter of the luminous body is nearly 6 arc minutes, with a faint halo extending out to over 15', half the apparent diameter of the Moon. 

The bright portion of the nebula is apparently expanding at a rate of 6.8 arc seconds per year, leading to an estimated age of 3000 to 4000 years. 

The central star of M27 is quite bright at mag 13.5, and an extremely hot bluish sub-dwarf dwarf at about 85,000 K (so the spectral type is given as O7 in the Sky Catalog 2000). K.L. Cudworth of the Yerkes Observatory found that it probably has a faint (mag 17) yellow companion at 6.5" in PA 214 (Burnham). 

The distance of M27 (and thus true dimension and intrinsic luminosity) is not very well known. Hynes gives about 800, Kenneth Glyn Jones 975, Mallas/Kreimer 1250 light years, while other estimates reach from 490 to 3500 light years. Currently, investigations with the Hubble Space Telescope are under work to determine a more reliable and accurate value for the distance of the Dumbbell Nebula. 

Adopting our value of 1,200 light years, the intrinsic luminosity of the gaseous nebula is about 100 times that of the Sun (about -0.5 Mag absolute) while the star is at about +6 (1/3 of the Sun) and the companion at +9..9.5 (nearly 100 times fainter than the Sun), all in the visual light part of the electromagnetic spectrum. That the nebula is so much brighter than the star shows that the star emits primarily highly energetic radiation of the non-visible part of the electro-magnetic spectrum, which is absorbed by exciting the nebula's gas, and re-emitted by the nebula, at last to a good part in the visible light. Actually, as for almost all planetary nebulae, most of the visible light is even emitted in one spectral line only, in the green light at 5007 Angstroms. 

Right ascension 19 : 57.4 (hours : minutes)
Declination +22 : 35 (degrees : minutes)
Distance 1,200 light years 
Visual magnitude 7.6

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