Saturday, March 19, 2011

Wide Field DSS2 image of NGC 7000, the North America Nebula

Wide Field DSS2 image of NGC 7000, the North America Nebula
Click on the image for full resolution (3.54 MB)

NGC 7000, the North America Nebula (Caldwell 20) is an emission nebula in the constellation Cygnus, close to Deneb (the tail of the swan and its brightest star). The remarkable shape of the emission nebula resembles that of the continent of North America, complete with a prominent Gulf of Mexico. The North America Nebula is large, covering an area of more than four times the size of the full moon; but its surface brightness is low, so normally it cannot be seen with the unaided eye. Binoculars and telescopes with large fields of view (approximately 3°) will show it as a foggy patch of light under sufficiently dark skies. However, using a UHC filter, which filters out some unwanted wavelengths of light, it can be seen by the naked eye under dark skies. Its prominent shape and especially its reddish color (from the hydrogen Hα emission line) show up only in photographs of the area.
Cygnus's Wall is a term for the "Mexico and Central America part" of the North America Nebula. The Cygnus Wall exhibits the most concentrated star formations in the nebula.
The North America Nebula and IC 5070, the nearby Pelican Nebula, are in fact parts of the same interstellar cloud of ionized hydrogen (H II region). IC 5070 is visible to the right of NGC 7000 in this picture. Between the Earth and the nebula complex lies a band of interstellar dust that absorbs the light of stars and nebulae behind it, and thereby determines the shape as we see it. The distance of the nebula complex is not precisely known, nor is the star responsible for ionizing the hydrogen so that it emits light. If the star inducing the ionization is Deneb, as some sources say, the nebula complex would be about 1800 light years distance, and its absolute size (6° apparent diameter on the sky) would be 100 light years.
The North America Nebula was discovered by William Herschel on October 24, 1786, from Slough, England.
The full resolution image weighs 3.54 MB, so please be patient when downloading!
Credit: Caltech/DSS2/; Processing: Jean-Baptiste Faure

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