From the USM Southworth Planetarium
“Just dandy”
THE DAILY ASTRONOMER
June 24, 2009
The Practical Astronomer: The Messier Objects
It is a fact universally acknowledged that any 18th/19th century astronomer who was desirous of fame must necessarily have discovered a comet which would forever after bare his/her name. This naming rule, still applicable, dates back to the early days of comet discovery. Edmond Halley (1656-1742), the one contemporary of Isaac Newton who actually got on well with him, was the first scientist to assert that comets could be periodic phenomena: i.e. they could return many times as they revolved around the Sun. Audacious for its times, Halley’s theory was ultimately proven correct when his namesake object, “Halley’s comet,” returned to Earth’s skies as predicted in December 1758. Unfortunately, Halley died more than a decade and a half prior to its return.
After the periodic nature of comets had been established, many astronomers devoted their careers to discovering and studying the orbits of new comets. This task was not an easy one, as the telescopes employed by these earlier astronomers were comparatively primitive with their low resolutions and meager light collection capacities. Despite these telescopic deficiencies, comet hunting was all the rage amongst the 18th/19th century astronomical community. As mentioned previously, finding a comet was a sure fire means of attaining a measure of immortality.
One comet hunter, Charles Messier (1730 – 1817), discovered more than a dozen comets. His fame, however, was assured by the catalog he compiled which listed “non-comets.” He developed this catalog to prevent other comet-hunting astronomers from mistakenly identifying certain objects such as nebulae as comets. When viewed telescopically, certain celestial bodies can closely resemble a comet, thereby causing the observer to inadvertently announce a false discovery. Messier reasoned that if all astronomers had access to a detailed listing of bodies that resembled comets, the number of false reports would be greatly reduced.
Messier published his first edition in 1771. This initial catalog listed 45 “Messier objects.” A 1784 edition increased this number to 103. Around the same time, collaborator Pierre Mechain augmented the collection with six more of his own objects. Astronomers still recognize these 110 Messier Objects. Almost all the star charts include the positions of these Messier bodies, which are designated by a capital M followed by their catalog designation number.
M1 is the “Crab Nebula,” located in the constellation Taurus the Bull. The Crab Nebula is a supernova remnant: a cloud of rapidly expanding debris produced by the explosion of a highly massive star. This nebula is believed to be the remains of the bright supernova observed in 1064 A.D.
M13 is the “Hercules Star Cluster,” located in the “keystone” section of Hercules. This globular cluster is a large assembly of more than 100,000 stars with a spherical distribution, hence the term “globular.” Many such globular clusters occupy the Halo: a region surrounding the galactic center. The Hercules Cluster is more than 25,000 light years away. Much closer in the Globular Cluster M4, which is only 7000 light years away.
M31 is the Great Galaxy in the constellation Andromeda. This monster galaxy is more than 2.2 million light years away. It’s original name was the “Andromeda Nebula,” a term coined when astronomers believed that most nebulae were gatherings of vapor amongst the stars. It was 20th century astronomer Edwin Hubble (1889-1953) who determined that these “vapor clouds” were actually mammoth star systems far beyond the edges of our Milky Way Galaxy.
Telescopes are required to view most Messier objects. Some are visible to the unaided eye, such as M44: the “Beehive Star Cluster,” which is the visible center in the nearly invisible constellation of Cancer the Crab. Cancer and M44 are in the western early evening sky. The Beehive Star Cluster, also known as “Praesepe,” resembles a splotch of faint white light just to the west of Leo the Lion’s sickle.
Most of the star charts and almanacs which feature the Messier objects will also have a legend specifying the type of Messier: they are generally nebulae, galaxies, or star clusters. Observers who are just starting to use telescopes and optical equipment are often encouraged to find these Messier objects first. They are, if you will, some of the easier targets in the vast field of deep sky objects. Messier hunting can lead to more challenging observations. So, Messier objects are like astronomy’s gateway drug.
