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Messier 78 - a reflection nebula complex in the
constellation Orion |
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Description of object:
In the center of our image - embedded in the dense dark molecular
cloud Orion B with abundant dust and cold gas - lies a complex of several
reflection nebulae. While in emission nebulae gas clouds are stimulated to glow
by ionisation of high-energy stars, in reflection nebulae the gas masses only
reflect the light of bright stars. Messier
78 is one of the brightest reflection nebulae in the sky and can
already be observed with smaller telescopes in dark environments. The distance
to the solar system is about 1500 to 1600 light years.
Messier 78 is
bounded at its upper edge by a prominent arc-shaped dark cloud which apparently
separates it from the adjacent nebula NGC 2067 above. In reality, however, this
dark cloud lies in front of the reflection nebula complex. The two bright stars
HD 38563 A and HD 38563 B produce a major part of the light that illuminates
the reflection nebulae. But the nebula accommodates many more stars, among
others a collection of 45 low-mass young stars, so-called T Tauri stars, which
are less than 10 million years old and hide behind the dust clouds.
About 1/4 degree northeast of M 78 is NGC 2071, a region of active star
formation, from where dense dust clouds extend northwest.
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In the
path of the dark cloud LDN 1627 in southern direction our image shows the two
Herbig Haro objects HH 19 and HH 24. They are generally very young stars which
repel matter clouds and then interact with surrounding dust clouds. Their color
is reddish, caused by a strong emission in sulfur light (SII). HH 19 is a
single star, whereas HH 24 consists of a small group of young stars.
South of HH 24 is a small, orange glowing nebula. It has the
catalogue number Be 106 and contains a young T Tauri star. T-Tauri stars are
extremely young stars which are less than 1 million years old. Because of their
small age these stars are not yet stable and mostly irregularly variable.
Messier 78 was discovered in March 1780 by the French astronomer and
geographer Pierre Méchain and was also described by Charles Messier in
late 1780. « The annotated image shows also a comparison to the size of
the full moon. |
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All Images and all
Content are © by Franz Hofmann + Wolfgang Paech |