NASA charmingly described galaxy Messier 74 back in December 2011 when it published a Hubble Space Telescope view of it: "Resembling festive lights on a holiday wreath, this image of the nearby spiral galaxy M74 is an iconic reminder of the impending season. Bright knots of glowing gas light up the spiral arms, indicating a rich environment of star formation."
M74, a relatively close spiral, is well placed for telescopic viewing in the fall through early winter. When members of the Salt Lake Astronomical Society visited the University of Utah's South Physics Building for an astrophotography session on Nov. 20, they first attempted to take photos of it but a few clouds soon glided over its location. Next try was for the enormous spiral galaxy M33, which succeeded. Much later, after clouds had cleared away, the group returned for a productive session with M74.
Guided by Paul Ricketts of the U.'s Physics and Astronomy Department, the group connected to the Willard L. Eccles Observatory at the top of Frisco Peak, elevation 9,629 feet. The $1 million-plus observatory, located near Milford, Beaver County, mounts a highly precise 32-inch-diameter telescope and a sophisticated CCD camera. The dome, telescope, camera and other fixtures are operated by remote control. The facility opened in 2009.
M74 lies an estimated 32 million light-years from our section of the universe and is deemed a grand design spiral, meaning it has symmetrical curving arms highlighted by dust lanes. Located in the constellation Pisces (Latin for fish, plural), it presents a face-on view. If it happened to be sideward, it would look something like a thick edge-on plate with a bulging center.
The M in M74 refers to Messier. In the late 1700s, the French observer Charles Messier was eager to discover new comets. These travelers usually look like a faint fuzzy patch when first discovered far from the sun; they grow their impressive tails when they glide to the inner solar system, where the solar wind — and presumably the warmer temperatures — blow dust and ice away from their nucleus. Before sprouting tails, they can look similar to stationary deep-space objects like galaxies and nebulas, especially when glimpsed through 18th-century telescopes.
Not wanting to be fooled by non-comets into making a false announcement of a comet find, Messier set out to catalog the stationary objects. He began with the Crab Nebula, which is the remains of a star in our galaxy that blew up in a supernova in 1054, designating it Messier 1, aka M1. (Not to wander too far from our story about M74, M1's progenitor star wasn't massive enough to form a black hole; instead, in the midst of expelled material that looks slightly like a crab, a spinning neutron star remains, sending out radio pulses at 30 times a second, according to NASA.)
Messier went on to list 110 objects, including tight star clusters, planetary nebulas, extended nebulas, loose star clusters and galaxies, which form a fine catalog for astronomers looking for interesting and not-too-dim deep space wonders.
In 1780, an assistant of Messier, the astronomer Pierre Mechain, discovered the galaxy. Robert Burnham Jr., in his classic "Burnham's Celestial Handbook, Vol. 3" (Dover Publications Inc., New York, paperback version, copyright 1978) quotes Mechain as writing that this object is "fairly large, very obscure and extremely difficult to observe." Messier confirmed the "nebula" the next month, October 1780, Burnham adds. It became the 74th entry on his list.
Although close as galaxies go, it is one of the faintest in the Messier catalog; M74 is best viewed in November. During the visit to the South Physics Building, the group photographed it with 25 exposures of five minutes' duration each, for a total of two hours, five minutes.
Discussions while the exposures were made covered several aspects of astrophotography, particularly the way black and white images are combined to produce a color product. A series of "luminous" photos — taken through no filter or only an infrared filter to reduce haze — forms the scaffolding for the finished view; these are shot at full scale. M74 posed for 10 photos of the luminous variety.
Pictures taken with red, blue and green filters often are made at half-scale because details in color aren't as important. Telling the camera to take photos that are less than full scale, called binned images, captures more light photons per exposure period. Detail is not as important in a binned color exposure. Think of the color views like watercolors brushed over a drawing.
Color data was recorded in five images, five minutes' exposure apiece, with each of the red, blue and green filters.
An ordinary laptop fitted with the right software combines the luminous, red, blue and green views into a single image showing detail and the full range of color. In addition to the basic luminous, red, blue and green photos, Ricketts made many other images that were used to remove glitches like electronic noise produced by the camera.
In the end, the team produced beautiful views of two of the most interesting spiral galaxies.