* Astronomy

NGC 6781 (also The Ghost of the Moon Nebula, IRAS 19160 + 0626, and PK 041-02 1) is a magnitude +11.4 planetary nebula located about 3,000 light-years away in the constellation Aquila.
The planetary nebula spans about 3', with a true diameter of about 2 light-years. The magnitude +16.9 central star has a mass of approximately 0.6 solar masses and an effective temperature of 100,000 degrees Celsius, making it one of the most luminous in the ultraviolet spectral region.

The nebula was discovered by German-British astronomer William Herschel using a 47.5 cm (18.7 inch) f/13 speculum reflector in Slough, Berkshire, on the 30th July 1788. 

Right Ascension 19h 18m 28.3s, Declination +06° 32' 19.3"

Within NGC 6781, shells of gas blown off from the faint, but very hot, central star's surface expand out into space. These shells shine under the harsh ultraviolet radiation from the progenitor star in intricate and beautiful patterns. The central star will steadily cool down and darken, eventually disappearing from view into cosmic oblivion. 
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