The Veil Nebula is the perfect example of a supernova
remnant and has an apparent diameter of 3 degrees in the sky. Our image shows
the eastern main segment, consisting of NGC 6992, 6995 and IC 1340.
The gas ejected by the supernova explosion expands and spreads out
almost spherically at about 180 kilometres per second, or nearly 600 000
kilometres per hour. In the process, it collides with the surrounding
interstellar medium, heating up to several million degrees and forming a
structure of luminous filaments and nebulae.
Depending on the chemical
elements present in the remnants of the stellar explosion, the gas is ionised
and begins to glow. In the case of the Veil Nebula, the elements hydrogen,
nitrogen and sulphur glow in red hues and the triply ionised oxygen in
brightest parts of the nebula were discovered by Friedrich Wilhelm Herschel in
1784. The southernmost part of NGC 6992 is catalogued as NGC 6995 and was
discovered in 1825 by John Herschel, Herschel's son, using his father's
telescope. The fainter parts of the nebula were discovered later - in 1866 and
1873 - by the American astronomer Truman Henry Safford (IC 1340) and by
Lawrence Parsons, the 4th Earl of Rosse (NGC 6974).
According to estimates, the supernova that formed the
Veil Nebula should have reached full moon brightness for several weeks and thus
should have been visible in the daytime sky. However, prehistoric observations
or descriptions are not known.
« Click here or the thumbnail to load a large annoted image
and a size comparison to the full moon.