30.7 MB (2.9 MB compressed)
3955 x 2709 pixels
33.5 x 22.9 cm ⏐ 13.2 x 9.0 in (300dpi)
ROBERT GENDLER / SCIENCE PHOTO LIBRARY ROBERT GENDLER / SCIENCE PHOTO LIBRARY
Trifid nebula (M20), optical image. This nebula is a region of star birth. The red area is an emission nebula, where radiation from hot, newly formed stars ionises the surrounding gas and causes it to glow. The blue area is a reflection nebula, which does not emit light, but reflects the light of nearby stars. Reflection nebulae appear blue because short-wavelength blue light is scattered more than red. The dark lines seen across the nebula are caused by dark dust clouds in the foreground that obscure the light from behind. The nebula lies in the constellation Sagittarius.
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