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Sh2 -73 is an emission nebula visible in the constellation of Hercules .
It is observed in the southwestern part of the constellation, on the border with the Head of the Snake and the Northern Crown ; looks like a faint filament barely perceptible in astronomical photos sensitive and completely invisible to the simple observation amateur. The best time for his observation in the evening sky from March to September and is visible from both hemispheres, although it is north of the ' celestial equator .
Sh2-73 is one of the clouds closer to the solar system , being just 200 parsecs (650 light years ); is located at a latitude galactic very high and does not appear associated with any star light, nor in it are active phenomena of star formation . [2] The cloud may be associated with MBM 40, a weak filament of gas not illuminated which contains 20 - 40 M ⊙ and located about 120 parsecs from the Sun . [4]
