Explanation:
Every book
has a first page and every catalog a first entry.
And so this lovely blue cosmic cloud begins the
van
den Bergh Catalog (vdB) of stars surrounded by reflection nebulae.
Interstellar dust clouds
reflecting the light of the nearby stars,
the nebulae usually appear blue because scattering by the dust grains
is more effective at shorter (bluer) wavelengths.
The same type of
scattering gives planet Earth its
blue
daytime skies.
Van den Bergh's 1966 list contains a total of 158 entries more
easily visible from the northern hemisphere, including
bright Pleiades
cluster stars and other popular targets for astroimagers.
Less than 5 light-years across,
VdB1 lies about 1,600 light-years distant in the constellation
Cassiopeia.
Also
on this scene, two intriguing nebulae at the right show loops and
outflow features associated with the energetic process of star formation.
Within are extremely young variable stars
V633 Cas
(top) and V376 Cas.
