Southern Colorado Skies / SEPTEMBER 2017



In the pre-dawn of September 10th, look for Mercury, Mars and Regulus (in Leo the Lion) in a close triangle. On September 12th Mercury will be at its greatest elongation (farthest from the Sun as seen from Earth), and on the 14th it will appear only 11 degrees below much brighter Venus. At dawn on September 16th look for Mercury less than 1/2 degree from Mars (see graphic); Mercury then fades out of view for the rest of the month.


Look for bright Venus low on the eastern horizon as it rises about 4 a.m. near the first of September, and about 5 a.m. at the end of the month. Venus presents us with a shrinking gibbous disk this month as it circles away from us toward the far side of the Sun. As a special treat, look for M44, the Beehive star cluster in Cancer (the Crab), about 1 degree to the left (east) of Venus. (See What is a Messier Object? later in this newsletter).


Mars is visible in the pre-fawn eastern sky, but binoculars will probably be required early in the month (watch out for the nearby Sun!!). Mars and Mercury will be less than 1/2 degree apart on September 16th (see graphic).


Look for Saturn about 25 degrees above the horizon in southwest about an hour after sunset (see graphic). Although Saturn’s disk shrinks slightly in size this month, its rings are close to their maximum opening in 15 years! This makes for a spectacular view in even through a small telescope. Because Saturn’s disk now casts its shadow on the rings, the disk and rings look more three-dimensional through a telescope.


Although Jupiter remains bright, it is fading fast from the sky. It starts September about 10 degrees above the horizon in the west-southwest about an hour after sunset, but ends the month only about 4 degrees high at dusk.


While searching the sky for their quarry, comet hunters are essentially looking for “fuzzy patches of light” and are often frustrated if they see several objects that fall into that category but turn out not to be comets after all. This type of frustration prompted Charles Messier, a French astronomer in eighteenth-century France and avid comet hunter, to begin assembling a catalog of “fuzzy patches” in 1758 “so that astronomers would not confuse these nebulae with comets just beginning to shine.” Today we know this list as the Messier Catalog, which consists of 110 deep-sky objects that are worthwhile and relatively easy for amateur astronomers to observe. These “nuisance objects” (as Messier called them) make a great beginning project for amateurs who are just getting into observations of deep-sky objects.

Messier’s list was officially published in 1774 with 45 deep-sky objects, and in 1780 Messier supplemented his list with 23 more objects. By 1781 there were 35 additional objects posted (24 from a colleague) for a total of 103 objects. Finally, seven more objects were added in the 1920s based on notes from Messier and his colleague.

Over the course of time astronomers have given names to some Messier objects often based on common items they resemble. Here are some examples:

M1             Crab Nebula (Taurus)                             M44                Beehive Cluster (Cancer)

M8            Lagoon Nebula (Sagittarius)                 M45*              Pleiades (Taurus)

M11          Wild Duck Cluster (Scutum)                   M51                Whirlpool Galaxy (Ursa Major)

M13          Great Hercules Cluster (Hercules)        M57                Ring Nebula (Lyra)

M31          Andromeda Galaxy (Andromeda)         M42    Orion Nebula (Orion)

* Also known as ‘The Seven Sisters’ or ‘Subaru’

An interesting fact is that all of the Messier objects may be observed during a single night! This is known as a “Messier Marathon” and may occur during a window lasting a few weeks between mid-March and early April. Here in Southern Colorado we are fairly well situated for such an event, as a latitude of around 25 degrees north (Pueblo is about 38 degrees north) is considered to be the best location to successfully complete a Messier marathon.


You may remember Andromeda as one of the principal characters in the movie Clash of the Titans. In Greek mythology, Andromeda was an Ethiopian princess and daughter of King Cepheus and Queen Cassiopeia (also with constellations of their own). Unfortunately, Cassiopeia was a bit vain and bragged the her and her daughter’s beauty rivaled that of the goddesses. Of course this meant trouble, and sure enough the sea-god Poseidon sent the whale Cetus (yet another constellation) to ravage their coastal property. To satisfy Poseidon, Andromeda was chained to a rock as a sacrifice to this sea monster. Luckily, the hero Perseus flew to her rescue on his winged horse Pegasus (two more constellations!) and slew the monster.

The constellation Andromeda is “chained” to one corner of Pegasus, and extends in a line of relatively faint stars to the northeast. At the end of a branching line (see graphic) is the Andromeda Galaxy (M31), easily visible with binoculars and even visible with a naked eye under dark seeing conditions – this galaxy is the most distant object a human eye can see at two million light years from us.



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