From Astronomy Magazine: “The Horsehead Nebula in Orion: An unbridled look”

From Astronomy Magazine

October 28, 2020
Eric Betz

The Horsehead Nebula [Barnard 33] has captured the public’s attention like few other celestial objects. And though its history is fascinating, it’s also mysterious.

The Horsehead Nebula [Barnard 33] and the Flame Nebula [NGC 2024] (left) in the constellation Orion are favorite telescope targets for amateur observers. Credit: Stephanh/Wikimedia Commons.

On the night of July 27, 1913, astronomer E. E. Barnard noticed that the skies above Yerkes Observatory in southern Wisconsin were nearly perfect.

U Chicago Yerkes Observatory.

The heavens were crystal clear and the Midwest air was surprisingly steady.

He guided the gaze of the world’s largest refracting telescope in the direction of Orion, targeting a mysterious object he’d tried to glimpse many times since his comet-hunting days decades earlier. Other astronomers had previously photographed the area, but the nature — and very existence — of one fuzzy spot remained controversial.

On this picturesque Wisconsin night, however, there was no mistaking it: A crisp, black silhouette stood out against a bright background sky.

“From the view, one would not question for a moment that a real object — dusty looking, but very feebly brighter than the night sky — occupies the place,” Barnard wrote. “This object has not received the attention it deserves,” he added.

Barnard also managed to capture a picture of the celestial object, which is still recognizable to space fans today. He had finally tamed the Horsehead Nebula, an object whose fame has since grown, spurred by an era of multi-billion-dollar space telescopes and advanced instruments for amateur astronomers.

Over a century ago, astronomer E. E. Barnard captured the zoomed in picture at left of what he dubbed Barnard 33, now known as the Horsehead Nebula. Credit E. E. Barnard/Yerkes Observatory.

The Horsehead Nebula in the constellation Orion has captured the public’s attention like few other celestial objects.

Orion Nebula ESO/VLT

Orion Molecular Cloud Complex-Credit Rogelio Bernal Andreo Wikimedia Commmons

It can rear up almost anywhere, from T-shirts at gift shops to shoulder tattoos to posters plastering the bedroom walls of young space fans. However, spotting the Horsehead Nebula in the real night sky is a bit tricky.

The Horsehead Nebula, also known as Barnard 33, and its companion, the Flame Nebula, sit near the star Alnitak in Orion’s Belt. Today, we know that the Horsehead is a dark, light-gobbling nebula made of cold gas and dust. And, as Barnard showed, this dark cloud’s signature shape is only visible because its silhouette obscures the light from the brighter nebula behind it.

The horse’s prominent “jaw” is actually shaped by intense radiation from a nearby star blowing on the dark cloud. And as easy as it is to focus on this charismatic object, the Horsehead Nebula is just one piece of the much larger Orion Molecular Cloud Complex. This star forming region spreads across hundreds of light-years and covers much of the Orion constellation itself. And by studying it, astronomers have learned the stellar nursery has already given birth to young stars, some even with protoplanetary disks.

But where is the Horsehead Nebula in Earth’s night sky? It’s location is surprisingly easy to find, but picking out the object itself is a bit harder. As mentioned, the Horsehead Nebula sits near Alnitak, also known as Zeta Orionis, which is the easternmost star in Orion’s Belt. You’ll can find the Horsehead Nebula grazing just to the south.

Its characteristic shape and vivid pink colors have made the Horsehead Nebula a tempting telescopic target for many years. But despite its popularity, the gas cloud is actually very faint.

The Horsehead Nebula sits a good distance from Earth — some 1,500 light-years away. As a result, it shines at just magnitude 6.8. To make matters even worse, there’s usually a relatively bright star in the same field of view. So, through a telescope eyepiece, the horsehead appears dim, small, and a bit washed out.

But because the Horsehead Nebula is so hard to spot, some amateur astronomers use it to their observing skills. That’s partly why, when this gas cloud was first spotted, its signature shape wasn’t even noticed.

How the Horsehead Nebula was discovered

The discovery story of the Horsehead Nebula is surprisingly muddled, especially for an object that’s so famous today. A number of astronomers stumbled across it over the years, but their limited instruments made it hard to carry out detailed studies.

The British astronomer William Herschel, discoverer of Uranus, may have been the first to see the Horsehead Nebula through a telescope. Herschel was a prolific observer and, in 1811, he submitted a paper boldly titled The Construction of the Heavens to the journal Philosophical Transactions. In one section, he laid out 52 different nebulous objects that he’d spotted in the night sky over his lifetime.

“They can only be seen when the air is perfectly clear, and when the observer has been in the dark long enough for the eye to recover from the impression of having been in the light,” Herschel wrote.

However, his descriptions of the objects themselves were frustratingly vague. They went largely ignored for nearly 100 years.

That’s when Welsh amateur astronomer Isaac Roberts decided to photograph the 52 locations Herschel mentioned. It took him six years to complete the task, and in a paper published in 1902, Roberts presented a largely critical take on the existence of Herschel’s nebulous targets.

There were a few objects that clearly stood out though. And one of the locations was a dead ringer for the location of the Horsehead Nebula, which Roberts managed to capture in a photograph. However, Roberts’ view was too faint to make out much detail. He went on to dismiss it as a mere “a stream of nebulosity.”

Meanwhile, around the turn of the century — and seemingly unbeknownst to many in the field, or simply left out of their publications — another astronomer had already discovered the object in her growing catalog.

Cutting edge science to desktop wallpaper

Williamina Fleming was a human “computer” employed by the Harvard College Observatory more than a century ago. The Scottish astronomer started her career as a maid in the home of Edward Charles Pickering, the observatory’s director. But she was soon hired to analyze stellar spectra — the chemical fingerprints of stars. Fleming’s system of classifying stars grew in popularity, and astronomers still use today.

Throughout her career, Fleming cataloged thousands of objects — and one of those was the Horsehead Nebula. In 1888, she was reviewing one of Pickering’s photographic plates when she spotted the nebulous object.

To her, it was simply one more nebulae out of the myriad other objects she cataloged during her lifetime. But, Fleming still gets credit for the first confirmed discovery of the Horsehead Nebula.

Horsehead Nebula Credit NASA/ ESA Hubble.

But that leaves another question: Who named the Horsehead Nebula? The historical record is vague on this point. It wasn’t Hershel or Fleming. Roberts didn’t use the term in his 1902 follow-up research, and Barnard didn’t seem to notice its equine similarities in his papers, either.

Even early popular references don’t seem to agree on what to call it. In 1922, a book called Astronomy for Young Folks referred to it as the “Dark Horse Nebula.” But the more familiar “Horsehead Nebula” was also common vernacular for astronomers during the early 1920s. However, the latter term came to dominate soon after, as more and more astronomers were able to capture detailed photographs of it.

By the dawn of the Space Race, the Horsehead Nebula was a favorite in astronomy books, magazines, and works of science-fiction.

Today, the Horsehead Nebula appears far more often in desktop wallpapers than it does in scientific papers. But that hasn’t stopped people from appreciating its beauty. Space fans all over the world love the charismatic cosmic equine. And its highly doubtful that’s going to change anytime soon.

See the full article here .


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Astronomy is a magazine about the science and hobby of astronomy. Based near Milwaukee in Waukesha, Wisconsin, it is produced by Kalmbach Publishing. Astronomy’s readers include those interested in astronomy and those who want to know about sky events, observing techniques, astrophotography, and amateur astronomy in general.

Astronomy was founded in 1973 by Stephen A. Walther, a graduate of the University of Wisconsin–Stevens Point and amateur astronomer. The first issue, August 1973, consisted of 48 pages with five feature articles and information about what to see in the sky that month. Issues contained astrophotos and illustrations created by astronomical artists. Walther had worked part time as a planetarium lecturer at the University of Wisconsin–Milwaukee and developed an interest in photographing constellations at an early age. Although even in childhood he was interested to obsession in Astronomy, he did so poorly in mathematics that his mother despaired that he would ever be able to earn a living. However he graduated in Journalism from the University of Wisconsin Stevens Point, and as a senior class project he created a business plan for a magazine for amateur astronomers. With the help of his brother David, he was able to bring the magazine to fruition. He died in 1977.