The Heart Nebula is an emission nebula in the constellation of Cassiopeia.  At its center the open cluster Melotte 15.  It is approx 7500 ly from earth, with an actual radius of 165 ly. The nebula has an apparent magnitude of 18.3 and an absolute magnitude of 6.5. It is 150 arcminutes in size. Its shape is driven by the stellar winds from the stars at its center. The colours are due to the presence of hydrogen (mapped to red), sulphur (mapped to yellow/green) and oxygen (mapped to blue) emissions. In this case mapping the sulfur emission, which is actually red, to yellow/green highlights the subtle variations in structure present in this wonderful nebula. This image is part of the “Colours” Showcase.

Celestron RASA 11″ 
10Micron GM1000 HPS 
SIGMA fp (monochrome) / SIGMA fp L (colour)
H-alpha / O-III / S-II ultra-fast narrowband filters,
21 x 4 min, ISO 1600, F2.2, 620mm 

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