Planetary nebula NGC 7662 in Andromeda

NGC 7662, a planetary nebula; the Blue Snowball


Description of NGC 7662 in
The Deep Sky Field Guide to Uranometria 2000:


A bright, slightly elliptical planetary nebula, measuring 32 x 28, bluish-green in color. Although discernible with very small telescopes as a nearly stellar object of magnitude 8.5 a visual observer needs a 6 inch scope and a magnification of at least 50x to see a hint of the softly glowing disc. In a 10-inch telescope the darker center gives it an annular appearance; the central star is a difficult object visually, but appears clearly on photographs.

The distances of the planetary nebulae are not known with any real accuracy. According to the Skalnate Pleso Catalogue (1951) the distance of NGC 7662 is about 1,800 light years, the actual diameter about 20,000 AU. In a survey of the brighter planetaries, C.R.O'Dell (1963) derived a distance of 1,740 parsecs or about 5,600 light years for this nebula, increasing the actual size to 0.8 light year, or nearly 50,000 AU. The central star is a bluish dwarf with a continuous spectrum and a computed temperature of about 75,000K. The nuclei of the planetary nebulae are among the hottest stars known.