The Horsehead Nebula lies some 1500 light-years away in the constellation of Orion, just south of Alnitak, the most easterly star in the famous belt. The nebula, also known as Barnard 33, spans approximately five light-years and is a popular viewing target for both amateur and professional astronomers.
The Hubble image marks the 23rd anniversary of the observatory's launch aboard the space shuttle Discovery on April 24, 1990. Unlike optical light images of the Horsehead Nebula, which appear dark and shadowy, Hubble's infrared view is rich with detail and appears almost transparent against the backdrop of the Milky Way. The image was taken using the Wide Field Camera 3, which was installed on the observatory in 2009.
The ultraviolet glare from the two bright stars visible along the nebula's top ridge is thought to be slowly evaporating the nebula itself, with some of the gas surrounding gas clouds having already disappeared.
Unlike the Hubble image, Herschel's view gives a wider perspective, showing the huge Orion molecular cloud, with the Horsehead itself visible on the far right of the image. The far-infrared Herschel view captures the glow from the dust and clouds of cold dust, materials that will eventually collapse to form stars.
In addition to the Horsehead itself, the image covers a number of well known objects such as the butterfly wing-like star formation sites NGC2068 and 2071, and the imposing Flame Nebula.
Unlike the Hubble telescope that will be in use for years to come, Herschel is nearing the end of its life span, with the superfluid helium used to cool its instruments and detectors all but gone.