M20 - Trifid nebula

M20 - Trifid nebula: The Trifid Nebula is one of several bright nebulae in the southern, summer milky way. It is easily seen with a small telescope or even binoculars if you know where to look. The trifid name comes from the three divisions seen in the reddish emission part of the nebula. Also prominent is the blue reflection nebula and the dusty "dark" nebula.

Messier: 20
NGC: 6514
Other Catalogs: Barnard 85
Right Ascension: 18 hrs 2 m
Declination: -23° 2'
Apparent Magnitude: 6.3

Date: June 2008
Equipment: Meade 10" f6.3 LX200
SBIG ST-10XE

Additional Comments: This is one of the several images taken with a 10" LX-200 temporarily installed in the dome in 2008 when the main circuit board for the 16" needed repair. See: http://www.fortlewis.edu/observatory/image_detail.asp?ID=120

When excited electrons in a hydrogen atom decay from a higher excited state into the first excited state, the photons emitted are part of the Balmer series. The lowest energy transition in this series is going from the second to the first excited state, in which case a red, H-alpha (656.3nm) photon is emitted. Going directly from the third excited state to the first excited state, the atom will emit an H-beta photon (486.1nm). When an electron decays to the ground state, which is a much larger energy drop, an ultraviolet photon is emitted. For more information, see: http://en.wikipedia.org/wiki/Balmer_series

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