The Crab Nebula is the remnant of the daylight supernova of 1054 AD. In the millennium since its formation, the nebula has expanded to a diameter of 10 light-years, with an average velocity of expansion of 1/2 % of the speed of light (about a thousand miles per second). The radiation of the nebula is caused by synchrotron radiation emitted by the millisecond pulsar at its center -- a neutron star rotating 30 times per second. (NASA, ESA, J. Hester, A. Loll (ASU); Acknowledgement: Davide De Martin (Skyfactory), apod091025)

     The Lagoon Nebula (M8) lies about 5000 light-years from the Earth, in the direction of the constellation of Sagittarius (and hence, toward the center of our galaxy). It is best seen telescopically at very low power, as its 100 light-year span is nearly three times the half-degree diameter of the Moon. As shown by the different appearance of the images above and below, its "color" depends upon the artistic whims of the the person who chooses the colors representing different wavelengths in or out of the visible spectrum. Its actual visual appearance is of a ghostly gray cloud spread across the starry background formed by stars lying between us and it, and within its star-forming regions.

The brighter parts of the nebula appear somewhat like a bird floating on a body of water, hence the "Swan". (Why "Omega" bears research). The brightest part of the nebula extend over 12 light years, but fainter clumps of gas cover 40 or more light years. The Swan is about 5700 light years from the Sun. (Adam Block/NOAO/AURA/NSF/NOAO)

M78 (= NGC 2067 and 2068) is a reflection nebula in the Orion molecular complex, about 1600 light years from Earth. In the image below, it is the bright bluish nebula near center. It is about 5 light years across, and unlike most such bright nebulae, is not shining itself, but merely scattering the light of hot, young blue giants behind it, and similar stars hidden from view by the dust clouds crossing it. For NGC catalog purposes, M78 is divided into two parts. The brighter region, framed by the semi-circular dark dust lane surrounding the left portion, is NGC 2068 (RA 05 46 46, Dec +00 04 45). The fainter region, to the north of the dust lane (in this image, to the right), is NGC 2067 (RA 05 46 32, Dec +00 07 52). The reflection nebula at the top of the image is not considered part of M78, and is referred to as NGC 2071. (T. A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and AURA/NSF/NOAO)