To the right is an image captured from the Wide-field Infrared Survey Explorer (WISE) telescope. The image shows three nebulae in the constellation of Orion and are located approximately 1,500 light years away from Earth. The nebulae shown are the Flame nebula, the Horsehead nebula and NGC 2023.
The Flame Nebula, also known as NGC 2024, is an emission nebula in the constellation Orion. An emission nebula is simply one that is being heated up from stars within its interior, and emitting light in various colors.
The Horsehead Nebula is a dark nebula that is on the lower right side of the vertical dust ridge. A dark nebula is one that is so dense that it obscures background light.
The final nebula is NGC 2023 which is a reflection nebula. A reflection nebula simply reflects light from nearby stars. This nebula can be seen as a bright circle in the lower half of the image.
The bright blue star on the right side of the nebula is Alnitak, which is the eastern most star of Orion’s belt.
Color in this image represents specific infrared wavelengths. Blue represents light emitted at 3.4-micron wavelengths, mainly from hot stars. Relatively cooler objects, such as the dust of the nebulae, appear green and red. Green represents 4.6-micron light and red represents 12-micron light.
This image was made from data collected after WISE began to run out of its supply of solid hydrogen cryogen in August 2010. Cryogen is a coolant used to make infrared detectors more sensitive. WISE mapped the entire sky by July using four infrared detectors, but during the period from August to October, 2010, while the cryogen was depleting, WISE had only three detectors operational, and the 12-micron detector was less sensitive. This turned out to be a good thing in the case of this image, because the less-sensitive detector reduced the glare of the Flame portion of the nebula enough to bring out details of the rest of the nebula.
Image Credit: NASA/JPL-Caltech/WISE Team
