Explanation:
Clouds of glowing hydrogen
gas mingle ominously with dark dust lanes in this
close-up of IC 1396, an active star
forming region some
2,000 light years away in the constellation Cepheus.
In this and other similar
emission
nebulae, energetic
ultraviolet light
from a hot young star strips electrons from the surrounding
hydrogen atoms.
As the electrons and atoms recombine they emit longer
wavelength, lower energy light in a well known characteristic pattern
of bright spectral lines.
At visible wavelengths, the strongest
emission line in this pattern is in the red part of the spectrum and is
known as "Hydrogen-alpha" or just
H-alpha.
Part of IPHAS,
a survey of H-alpha emission in our Milky Way Galaxy,
this
image spans about 20 light-years and highlights
bright, dense regions within IC 1396, likely sites where
massive new stars are born.
