Colorado Skies: Behold the wonder of the Milky Way

Of the myriad celestial wonders that greet observers of the late summertime Colorado sky, none is more impressive than the faint irregular band of light that we call the Milky Way. Stretching across the early evening sky from the famed “W” of the constellation of Cassiopeia to the northeast all the way to the Sagittarius “Teapot” to the southwest, the Milky Way unfortunately has become more difficult to view from Fort Collins in light of, literally, an ever-increasing sky-glow rising from an ever-growing Larimer County populace. However, if one takes the time to find a dark observing site on a moonless night, the Milky Way glories visible to even the unaided eye are well worth the effort.

As one might suspect, such a prominent band of light has generated a wealth of mythology and folklore throughout the ages. Among the most common legends are those which consider the Milky Way to be a sort of “Highway to Heaven.” Such was the case for cultures as diverse as the Chinese, Hindus and the Native Americans. The Algonquin tribe of Canada carried the imagery a step farther in their belief that the bright stars which lined the Milky Way were the campfires of those departed souls on their celestial journey to the hereafter. Other cultures envisioned the Milky Way variously as a mighty celestial river flowing across the heavens, milk flowing from the breast of a goddess, a belt of snow, a band of golden star dust and a cloud-eating shark.

Early attempts at more rational explanations for the Milky Way fared little better. No less a personage than the great Greek philosopher Aristotle believed that the Milky Way was the result of “dry exhalations” or vapors expelled from the earth’s interior which upon contact with the heavens formed the Milky Way mists, much as the breath exhaled by a person on a cold winter day becomes visible as a misty cloud. Another Greek philosopher named Democritus who in the 4th century BC proposed a primitive version of our modern atomic theory of matter, did quite a bit better when he proposed that the seemingly solid Milky Way was in actuality composed of a countless number of atomic-size points of light, a view which turned out to be remarkably close to the truth.

More than 2,000 years later, the first telescopic views of the Milky Way revealed that it was indeed composed of tiny point-like images of light, but with the caveat that Democritus could not possibly have imagined in even his wildest speculations. Each of these point-like images has been found to be in fact a fiery star comparable to our own sun in terms of size and energy out-put, but located at distances which even now are scarcely imaginable.

We now know that the Milky Way is a vast and complex system of stars, gas and dust which is in the shape of a flat barred pinwheel over 100,000 light years in diameter. Within the confines of the Milky Way Galaxy, as it is now called, it is estimated that over 100 billion stars swing about the center of this pinwheel in vast orbits thousands of light years in size over periods of millions of years. Our solar system is moving in one such orbit which carries us in a circular path about the center of the Milky Way Galaxy once every 200 million years at a nearly constant distance of some 28,000 light years. From our vantage point in the “galactic hinterlands,” we see the rest of the Milky Way as an irregular band of light that is most prominent in the direction of the bulging galactic center which is framed by the stars of the constellation of Sagittarius. For southern hemisphere observers, Sagittarius is very nearly overhead and both branches of the central Milky Way sprawl across the heavens in glorious grandeur. Unfortunately, Sagittarius is just above the southern horizon when viewed from mid-northern latitudes, and as a result, only the northern branch of this richest region of the Milky Way is accessible to interested observers. It is nonetheless a fabulous part of the sky, well worth exploring with the naked, eye, binocular, or a small wide-field telescope on any dark, crisp, and clear late summer or early autumn night.

Elsewhere in the sky: A much-faded planet Mars is now located on the Scorpius-Sagittarius border, but is still brighter than either its “rival” Antares or the golden planet Saturn, both of which are situated a half of a constellation further to the west.

The planet Venus can be seen just above the western horizon for about an hour or so after sunset.

The planet Mercury moves into the predawn sky for its best morning appearance of 2016. Look for this elusive world above the eastern horizon about an hour before sunrise during the last week of September.

The planet Jupiter is too close to the sun to be easily seen in September.