M20 The Trifid Nebula (NGC 6514)

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The Trifid Nebula is a stunning combination of red emission nebula and blue reflection nebula.  The red comes from Hydrogen that is being excited by strong ultraviolet light from the nearby stars.  Hydrogen gas absorbs an ultraviolet light photon from nearby stars.  The excited "heated" hydrogen then emits a photon of slightly less energy with a characteristic red wavelength.  Light at this wavelength is known to astrophotographers as Hydrogen alpha. 

The blue light of the reflection nebula begins as white light from the nearby stars.  The white light is scattered in a similar process to how light from our Sun is scattered in the Earth's sky.  This process is known as Rayleigh scattering and results in the sky blue appearance of a reflection nebula.

For older (embarrasing) M20 image click the links below:

M20 Trifid 25Sep06   (8" Schmidt Newtonian, MPCC Coma Corrector, UHC-S filter, 4x4Mins ISO 1600)

Lagoon (M8) with Trifid Nebula (M20) in widefield (2 degrees - Orion 80ED 24Jun06)  (Guided 7 x 4mins ISO 800)

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