Serpens is a unique constellation, for it is split into two separate halves. It represents a snake coiled around the serpent holder, Ophiuchus. On one side of Ophiuchus lies Serpens Caput, the serpent’s head, which is the larger and more prominent half; on the other side of Ophiuchus lies Serpens Cauda, the serpent’s tail.
Within the boundaries of the serpent’s tail, Serpens Cauda, and just 3° north of the Swan Nebula, backyard astronomers will find a large scattered star cluster immersed in a vast diffuse nebula. This is the Eagle Nebula, also known as M16, one of the showcases of the night sky.
The M16 complex is visible to the naked eye on clear nights as a hazy patch, located in the northern end of a large S-shaped asterism of stars. Small telescopes show about five dozen suns scattered across half a degree of sky, members of the NGC 6611 cluster, within the nebula. The nebulosity threaded among the cluster stars is modestly bright at best, even with larger apertures, as the illuminated emission part of the nebula is not especially radiant.
Without UHC or O-III filters, many observers will be completely unaware of the nebulosity, even more the “eagle” itself, a classic dark gaseous formation superimposed on the whole. Just how much of the fantastic diffuse and dark nebulae that you will actually see depends on your specific circumstances and the light grasp of your telescope.
The Eagle Nebula contains the famous “Pillars of Creation”, fingers of dark nebulosity associated with ongoing star formation, imaged by the Hubble Space Telescope in 1995. The longest of the “Pillars” is seven light-years across; the other two are six and three light-years long, respectively. At each “Pillar” end, the intense radiation of bright young stars causes low-density material to boil away.
Due to the 7,000 light-years that separate us from the nebula, the “Pillars of Creation” may already be gone. In 2007 scientists using the Spitzer Space Telescope discovered evidence that indicates that the “Pillars” were destroyed by a nearby supernova explosion about 6,000 years ago, but the light showing the new shape of the nebula will not reach the Earth for another millennium.
Finder map – field width 10°, stars to magnitude +8.5.