Explanation:
At the edge of a large
molecular cloud in Monoceros,
some 3,000 light years away,
dark filaments of dust are silhouetted by luminous
hydrogen gas.
The close up view of the
Rosette
Nebula dramatically
suggests that star formation is an
on going process in the region, with dark filaments
sculpted
by winds and radiation from hot, young stars.
Ultraviolet radiation from the young stars also
strips electrons
from the surrounding hydrogen atoms.
As 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 25 light-years.
