Rising from a sea of dust and gas, the Horsehead Nebula is one of the most photographed objects in the sky. It is also known as a challenging target for backyard astronomers.

So to celebrate the Hubble Space Telescope's 11th birthday, researchers pointed the orbiting observatory at the imaginary horse head, which fills a detailed new photograph released today. The nebula, also known as Barnard 33, is a cold, dark cloud of gas and dust, silhouetted against a bright nebula called IC 434.

The bright area at the top left edge of the image is a young star still embedded in its nursery of gas and dust. Radiation from this hot star is eroding its gaseous birthplace. A massive star located outside Hubble's view uses its light to sculpt the top of the horse's head.

The nebula's unusual shape was first discovered in the late 1800s. It is located in the constellation Orion and is a cousin of the famous pillars of dust and gas known as the Eagle Nebula. Both tower-like nebulae are cocoons of young stars.

The Horsehead Nebula lies about 1,600 light-years away, just south of the bright star Zeta Orionis, which is easily visible to the unaided eye as the left-hand star in the line of three that form Orion's belt. Amateur astronomers often use the Horsehead as a test of their observing skills, in part because it is known as one of the more difficult objects to observe visually with an amateur-sized telescope.

The Horsehead Nebula was chosen last year by more than 5,000 Internet voters who were invited to select a target for the birthday shot. The image has been superimposed on ground-based data acquired by the 35-inch (0.9-meter) telescope at the National Science Foundation's Kitt Peak National Observatory in Tucson, Arizona.

The Hubble exposures were made in August and September 2000, as well as January and February 2001, and totaled 4.6 hours. The image shows an area that is roughly 2.2 light-years across.

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