Editor's note: This is based on a post on the author's blog.
Nothing in astronomy captures the imagination like the Horsehead Nebula.
It takes the form of the head and neck of a mighty phantom horse, a dark ghostly beast with a roiling mane, seen against a glowing pinkish curtain that is streaked with vertical folds and mysterious horizontal waves — all of it spattered with random white spheres. The spheres are stars, gigantic nuclear furnaces like our sun.
For many, it’s the loveliest and most dramatic thing up there.
In December 1999, NASA’s Jet Propulsion Laboratory, in Pasadena, California, called it a “heavenly icon” and wrote that it was “the clear winner among more than 5,000 internet voters, who were asked last year to select an astronomical target for the Hubble telescope to observe.”
Yet as beloved as it is to astronomers and the public, few have looked at it directly. I could never view it through my telescope, but I photographed it.
The mass of gas and dust is just too dim to register to the eye looking through most amateur-level instruments, and even using some that are fairly advanced.
Adding to the difficulty of seeing the dim nebula is its closeness to Alnitak, the left-most star in the belt of the great winter constellation Orion. The star dominates the telescopic scene, washing out the nebula.
Looking through my 12-inch diameter telescope, which has good light-gathering ability, I couldn't even glimpse an outline. But one may take long exposures with an astronomical camera hooked to a telescope. Photons slide through the lenses and drip onto the camera's sensitive chip, where they collect and the signal is multiplied. This makes up an image. Stack enough of these exposures precisely on top of one another, and a dim object becomes vividly visible.
The Horsehead is one of several impressive nebulas in Orion. Located about 1,500 light-years away (assignment: light whizzes along at 186,000 miles per second; how far will it travel in 1,500 years?), it’s a molecular cloud with the designation Barnard 33. AmazingSpace.org, an educational site operated by the Hubble and James Webb Science Missions, estimates the nebula is 2 to 3 light-years across.
At that distance, it is a tiny object to examine.
Molecular clouds such as Bernard 33 are accumulations of dust and hydrogen gas; the hydrogen is in the form of molecules, not individual atoms. According to Swinburne University of Technology (online at astronomy.swin.edu.au), in Melbourne, Australia, star formation takes place only within molecular clouds.
As part of a molecular cloud compresses due to gravity, it grows more and more compact. Eventually, enough mass is concentrated that nuclear fusion occurs and a star blazes forth. In the Horsehead Nebula, such a star is emerging between the ear and the top of the mane.
The “curtain” behind the horse is another type of celestial dust-and-gas cloud called an emission nebula. This is a former dark nebula that now is blasted with ultraviolet radiation from nearby stars, causing it to fluoresce. The bright nebula is designated IC 434, and is part of a gigantic star-birth nebulosity in Orion.
To photograph the Horsehead, I needed to focus on Alnitak and then aim to the right, where the Horsehead rears. Several exposures were required to center it properly. Then, electronically locking the small guide scope onto a star so the system would track properly, I could take views of the nebula.
In October 2014, I tackled the project from a site called Lakeside in Tooele County, where Salt Lake City’s light pollution isn’t too severe. It took two nights, Oct. 24-25 and Oct. 29-30, working through a slew of glitches with my equipment and suffering from the cold. The first night’s work was a complete loss.
The temperature fell to 27 degrees during the next try. As the night dragged on, I shivered in my ski mask, mad bomber hat, jacket and two heavy coats. To warm up, I sometimes climbed into the Jeep and got under my sleeping bag and a blanket. The camera’s exposures totaled four and a half hours. In the morning, my water jar was iced up.
Back home, I processed the photos and there it was: the stunning, eerie and elusive Horsehead!
Joe Bauman writes an astronomy blog at the-nightly-news.com and is the vice president of the Salt Lake Astronomical Society, which meets the third Wednesday of every month but December (see slas.us). Please contact him at [email protected].