NGC 3918

NGC 3918 is located in the southern constellation of Centaurus. Its far-southern declination means it is essentially unobservable from most northern latitudes. It ranks among the brightest planetary nebulae visible from the Southern Hemisphere.

NGC 3918 was discovered by the English astronomer John Herschel in March 1834 during his survey of the southern sky from the Cape of Good Hope in South Africa. Herschel was the son of William Herschel, the discoverer of Uranus. John Herschel's southern-sky cataloging work was foundational for later observatories in the Southern Hemisphere.

Yes, NGC 3918 is among the brightest planetary nebulae in the southern sky and can be observed with a modest amateur telescope. It appears as a small, bluish-green disc that can be mistaken for a planet at low magnification, which is how planetary nebulae got their name. A telescope with at least a 6-inch aperture under dark skies will reveal its disc clearly.

The blue-green appearance of NGC 3918 is caused by emission from ionized oxygen atoms in the nebula's expanding gas shell, excited by ultraviolet radiation from the central dying star. This is similar to the greenish-blue glow seen in other planetary nebulae. The nebula consists of material ejected by the star during its late-stage evolution.