Editor's note: A version of this was previously published on the author's website.
We had just called on a globular star cluster and Paul Ricketts wondered where our next adventure should take place. Knowing he likes nebulas, I suggested we try to photograph one. He chose a complex, sprawling, breathtaking example in the summer sky, the Eagle Nebula. Ricketts ordered the University of Utah’s great 32-inch-diameter telescope to move toward the nebula, technically named Messier 16, known as M16, and the instrument began to shift position.
This was June 30, a Saturday night. A few members of the Utah Astronomy Club had joined Ricketts, of the U.’s Department of Physics and Astronomy, for an excursion through the stars, courtesy of the Willard L. Eccles Observatory. Although the observatory is a green steel dome and control building atop the 9,550-foot Frisco Peak near Milford, Beaver County, the explorers sat comfortably in the South Physics Building on campus, 175 crow-miles to the northeast, while Ricketts sent commands by remote control.
The first target that session was M13, the dramatic globular cluster in the constellation Hercules. Like the Eagle, the Hercules Cluster is a famous highlight of the summer night sky. Globular clusters are dense balls of hundreds of thousands or a million ancient stars, held together by gravity for 12 billion years or even as long as 13.4 billion years. Since the universe erupted about 13.8 billion years ago, globulars are the oldest objects we can see easily. They orbit the centers of big galaxies, dipping into and out of the galaxy plane. Some of the Milky Way's estimated 150 globulars are so close and bright that they show up in binoculars as blurs. To the naked eye, a nearby globular looks like a fuzzy star.
The other known variety of star cluster, the open cluster, is almost the opposite of a globular. Its members can be young, having condensed recently from clouds of gas and dust within a galaxy, or as old as 8 billion years. Occasionally, wisps or dense clouds of the primordial nebula remain with some younger ones, while in their older siblings the original material has been used up or blown away by the stellar wind. An open cluster is localized inside a galaxy and far less densely crammed than a globular, typically with hundreds or a few thousand stars.
Open clusters generally are smaller than globulars. While the globular M13 is 150 light-years from side to side, an open cluster such as M35 may be 30 light-years across.
The Eagle Nebula is a remnant of gas and dust where stars are still emerging, stretching about 70 light-years by 55 light-years, NASA estimates. The sprawling nebula is in the constellation Serpens, the serpent, and is at its best position for Northern Hemisphere observation in July.
The Eagle's open cluster is "very young and it is embedded in a star-forming region" of the Milky Way, says a June 2016 study published by the National Research Institute of Astronomy and Geophysics, Cairo, Egypt. Scientists from that organization and Egypt's Computer Science Higher Technological Institute analyzed 78 CCD images to determine optical properties that helped date the cluster's stars. They found that the cluster is about 7,175 light-years away and around 3.6 million years old.
The most famous parts of the Eagle Nebula are what look like fingers stretching out in its center, a feature dubbed the "Pillars of Creation." Between 4 and 5 light-years long (twice the distance from the sun to the closest star), according to NASA, the "towering tendrils of cosmic dust and gas ... are part of an active star-forming region within the nebula" that "hide newborn stars in their wispy columns."
Hubble Space Telescope astronomers describe the pillars as "actually columns of cool interstellar hydrogen gas and dust that are also incubators for new stars. The pillars protrude from the interior wall of a dark molecular cloud like stalagmites from the floor of a cavern."
"A torrent of ultraviolet light from a band of massive, hot, young stars ... is eroding the pillar," explains the Hubble team. "The starlight also is responsible for illuminating the tower's rough surface. Ghostly streamers of gas can be seen boiling off this surface, creating the haze around the structure and highlighting its three-dimensional shape. The column is silhouetted against the background glow of more distant gas."
As stars continue to draw in and compress this gaseous material and as light from blazing new stars blows away the lighter gas and dust, the nebulosity will evaporate. Thousands of years from now, the Eagle Nebula should be reduced to a scattering of stars in an open cluster.
Through the evening, conversations ranged through topics such as exposure, car trouble, telescope setup, how to keep one's spouse happy while purchasing equipment, writing, processing software, science and lightning. Some of them like lightning. I don't. Of course, that prompted me to tell the story of how an airplane we were in was slammed by a bolt one night while flying over the Pacific heading toward the Philippines, knocking out an engine.
The feeling in that small section of the building was one of camaraderie, learning and deep appreciation of nature. To examine stunning sections of the cosmos was both humbling and uplifting.
Bryan Kay Carter and his wife, Lana, of Kaysville were among those attending. The session "gave us the opportunity to see the controls up close and have a discussion about what was happening," Bryan Carter noted after the meeting.
"I am relatively new to astrophotography, and I was very interested to see the setup. ... It was fascinating to watch the images come on the screen. Each one had a little more detail and it was amazing what can be seen with that scope! What an experience!"
Carter later assembled an impressive view of the nebula, using raw images that Ricketts put on line.
Spencer Hinckley, of North Salt Lake, said it's his "sincere hope that these events will continue in the future because it was an opportunity with my daughter. I believe every opportunity should be taken to teach a love of science, math, reading and art." Visiting with Ricketts and the group gave his daughter, Zoey Hinckley, 5, and him "an opportunity to stay up late talking about the stars."