NGC 3918 is a bright
planetary nebula in the
constellation
A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object.
The origins of the e ...
Centaurus, nicknamed the "Blue Planetary" or "The Southerner". It is the
brightest of the far southern planetary nebulae. This nebula was discovered by Sir
John Herschel
Sir John Frederick William Herschel, 1st Baronet (; 7 March 1792 – 11 May 1871) was an English polymath active as a mathematician, astronomer, chemist, inventor, experimental photographer who invented the blueprint and did botanical wor ...
in March 1834 and is easily visible through small telescopes. The round or even slightly oval diameter is telescopically between 8 and 10
arcsec, though deep images extends this to about 19 or 20 arcsec. More surprising is the beautiful rich blue colour that looks much like the coloured images of
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
taken by
Voyager 2 in 1989.
Spectroscopy reveals NGC 3918 is approaching us at 17±3.0 kilometres per second, while the nebulosity is expanding at around 24 kilometres per second. The central star is 14.6 visible light magnitude, and remains invisible to optical observers, as it is obscured by the sheer brightness of the surrounding nebula.
The distance is estimated at 1.5
kpc (4 900
light-years).
See also
*
List of NGC objects
*
List of planetary nebulae
References
External links
*
{{DEFAULTSORT:NGC 3918
Planetary nebulae
Centaurus
3918