This mosaic image was taken by NASA’s Wide-field Infrared Survey Explorer (WISE).
The Flame nebula shines due to the bright blue star seen to the right of the central cloud. This star, Alnitak, is the easternmost star in Orion’s belt. The Flame nebula glows in visible light due to the wind and radiation striking it from Alnitak. In this image, the infrared glow is from the dust warmed by Alnitak’s radiation.
The Horsehead nubula is visible in the WISE image as a faint loop protruding from the vertical band of dust band about one quarter of the way from the bottom of the image. Its position can be seen clearly in this image. The Horsehead is classified as a dark nebula because it blocks the visible light from the glowing gases behind it. The infrared detectors on WISE see the glowing dust from the nebula, which blends it into the surrounding landscape.
NGC 2023, can be seen as a bright circular object in the lower half of the image. NGC 2023 is a reflection nebula. The visble light that is reflected comes from the HD 37903, a luminous blue white B star. Here, WISE sees the infrared glow of the dust, and not the blue white reflected light.