NGC 3918

NGC 3918 is a bright planetary nebula in the constellation Centaurus. Its distance is about 4,900 light-years and he is the brightest of the southern planetary nebulae. NGC 3918 was discovered in March 1834 by John Herschel. One can already see with a small telescope in the sky the fog. Its slightly oval shape extending over eight to ten minutes of arc.

Fluorescence

A characteristic feature of NGC 3918 is its brilliant blue color. In the center of the object is a white dwarf. He is the remnant of a red giant and is obscured by the fog. This nucleus emits an intense ultraviolet radiation which excites the surrounding mist gas to fluoresce.

Dynamics

Spectroscopic data show that per second to move the object with about 17 miles on us. The mist itself ( its outermost gas layers ) expands at a speed of 97 kilometers per second.

A red giant star encounters in its final phase from large amounts of gas. This leads to the formation of such planetary nebula. NGC 3918 shows a bright glowing inner gas shell and further out a second more diffuse gas envelope. This gives the impression that the two layers derived from two separate ejections. According to studies, but both layers originate from the same outbreak. However, they blew the original red giant star 's different layers of gas away at two different speeds of itself.

The life span of such an object is several tens of thousand years. Fog as NGC 3918 exist only for a relatively short time, as they fade quickly due to the high propagation speed of the mist gas.