Lynn Savage, firstname.lastname@example.org
In December, NASA’s Wide-field
Infrared Survey Explorer (WISE) celebrated one full year of exploring the universe
using four different bands of IR detection. The image here represents just a small
fraction of the sky catalogued by the satellite during its operational run.
The image shows three nebulae that are part of the Orion molecular
cloud: the Flame nebula, the Horsehead nebula and NGC 2023. The Flame nebula appears
to be kindled by the bright blue star to the right of the central cloud. This star,
dubbed Alnitak, is the easternmost star in the belt of the constellation Orion.
The radiance captured by the satellite’s imagers originates from dust that
has been heated by Alnitak.
Image courtesy of NASA.
NGC 2023 can be seen as a bright circle in the lower part of the
image. It is a reflection nebula, meaning that the dust is reflecting the visible
light of nearby stars. WISE, however, sees the IR glow of the warmed dust itself.
Between NGC 2023 and the Flame, the famous Horsehead nebula appears
as a ghostly bump on the lower right of the vertical dust ridge. In visible wavelengths,
the Horsehead is easily discerned; again, the IR detectors aboard WISE peer into
the cloud to see the glow of the interstellar dust.
WISE incorporates four sensors, each with 1024 x 1024 pixels,
recording near-IR bands at 3.4 and 4.6 μm and mid-IR bands at 12 and 22 µm.
The near-IR sensors are composed of HgCdTe; the mid-IR ones, Si:As. Blue represents
light emitted at 3.4 μm, which comes mainly from hot stars. Relatively cooler
objects, such as the dust of the nebulae, are shown as green (4.6 μm) and red
(12 μm). The image was made from data collected after WISE (as expected) began
to run out of its supply of solid hydrogen cryogen almost nine months into its mission.
From August to October 2010, while the cryogen was depleting, the satellite had
only three detectors operational, and the 12-μm detector was less sensitive.
This turned out to be a good thing, because the less sensitive detector reduced
the glare of the Flame portion of the nebula enough to bring out the details in
the rest of the image.