click here for a full-resolution view)
The Heart Nebula is at a distance of 7,500 light years from earth in the Perseus arm of our galaxy. It spans 200 lightyears! The nebula is ionized by the relatively young stars at the center of the nebula (their open star cluster is known as Melotte 15). The nebula is 150 arcminutes in size (the moon is 30 arcminutes!) in the constellation Casiopeia.
It was discovered by William Herschel on November 3rd 1787 (he first discovered the brightest part in the lower left - NGC 896).
Being a mosaic there is SO much interesting detail here:
1. The bright NGC 896
2. The open star cluster Melotte 15 at the core
3. Beautiful dust pillars (created by the energetic light from the young, hot stars at the center)
Each of the four panels has and integration time of 10 hours (10xHa, 20xOIII, 40xSII - each 10 minutes). I think this is the longest integration time I ever had.