SEPTEMBER  2012

SEPTEMBER STAR MAP | STARWATCH INDEX | MOON PHASE CALENDAR

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837    SEPTEMBER 2, 2012:   Moon to Occult Ceres

When the Italian astronomer Giuseppe Piazzi discovered Ceres on January 1, 1801, he thought that he had revealed one of the “missing links” of the solar system. Nearly thirty years earlier, two German astronomers, Johann Bode and Johann Titius had independently formulated a numerical progression which explained accurately the distances of the known planets at that time. There was a catch. The Bode-Titius rule put an unknown planet in a position 2.8 times the Earth-sun distance, but that was exactly where Ceres was discovered. Twenty years earlier, William Herschel found Uranus which was also foreseen by the rule. In the end, Neptune deviated from a Bode-Titius prediction, as did Ceres, the first of nearly a million objects discovered to date which are now called asteroids. These findings helped to discredit the Bode-Titius rule among professional astronomers. Texas-sized Ceres has also has been reclassified as a dwarf planet. It does, however, meet three out of the four characteristics for planetary status. It is round, orbits the sun, and is not a satellite of another planet; but unlike the planets, it does not possess enough mass, and therefore, not enough gravity to clear its orbital space. If you want to see a Ceres, set your sights on Sunday morning, September 9, when a thick waning crescent moon occults, or hides, the dwarf planet. A small telescope will be mandatory in order to view the Ceres occultation successfully. On the East Coast the event occurs about 4:20 a.m., but on the West Coast, subtract the three hour time change, and also an additional 30 minutes for the positional difference of the moon. That would make the time when Ceres vanishes behind the moon about 12:50 a.m. It would still be wise to set up about half an hour before the event to monitor the slow, inexorable movement of Luna’s bright limb nearing Ceres. Much success!

838    SEPTEMBER 9, 2012:   Dance, Prancing Horse, Dance

This is one of the best times of the year to view the Milky Way in its entire splendor, for just after dark it arcs across the sky from west of south almost up to the zenith, and then down into the NE where it cuts back into the horizon. It may mean traveling 50 or 100 miles or more to escape the domes of light that blossom from our cityscapes, but if you have never seen the beauty of our home galaxy against a truly black sky, it may be worth the effort. Today, more than half of the world’s population has never seen our home galaxy, and that statistic holds true for the US as well. National parks and rural state parks offer the best prospects of catching stunning views of our galaxy. To see the best of the summer Milky Way, enthusiasts should find a rural location with a good southern view. From there, right after dark in mid-September, the central bulge of the Milky Way, where the oldest stars reside, will just be above the horizon, flanked on either side by the star patterns of Sagittarius the Archer and Scorpius the Scorpion. It’s easy to follow the galaxy upward through the great rift where over eons of time dust from countless supernovas has seemed to split the central plane of our galaxy, then past the cotton candy star clouds bracketed by the Great Summer Triangle and into the NE where the ethereal haze of countless stars begins to fade. To judge whether the sky is really supporting a good view, I have used the Prancing Horse as my barometer. It is created by dark obscuring dust clouds which are silhouetted against a somewhat brighter starry background where there is less dust. Located above the Scorpion’s tail and to the right of Sagittarius, it takes almost no imagination to see, if sky conditions will permit (photo online). A prancing horse dancing in your southern sky is reason to celebrate because you are witnessing the darkest of the temperate, late summer nights.

The ability to view the darker Prancing Horse: (within the oval) against the brighter star clouds of the Milky Way signifies the best sky conditions that summer has to offer. Photo by Gary A. Becker from the Mars Habitat near Hanksville, Utah...

The summer Milky Way arches across the sky near Hanksville, Utah at the Mars Habitat. The greenish hue near the left and right horizons on the photo represents a diffuse auroral glow that was present during several nights of my stay. North is to the left. The Prancing Horse can be found at the extreme right, center of the photo. Fisheye image by Gary A. Becker...

839    SEPTEMBER 16, 2012:   Goodbye Summer, Hello Fall

As much as I hate to admit it, autumn is not just around the corner, but it officially arrives on Saturday, September 22, at 10:47 a.m. Already I have seen that first big push of cooler, drier air heralding the fall season invade the mid-Atlantic. Saturated turquoise skies by day have given way to crisp, chilly evenings after sundown. Astronomically, we are in the biggest downward shift of the year with the sun headed southward at an accelerated pace causing the days to shorten and the nights to lengthen at their fastest rate. Depending upon where you live in the continental US, the amount of daytime lost since the high solstice sun of June 20 has been between two and three hours. Currently at the autumnal equinox, when the days and night are of equal length, we are in the middle of that downward spiral with another two to three hours of sun to lose before the long nights surrounding the time of the winter solstice on December 21. My Moravian College students are watching this transition right now, by climbing to the third floor rooftop observatory of the Collier Hall of Science and watching the sun set against the jagged horizon of trees visible from that vantage point. What they are noticing is a sun that is setting ever farther to the south in a relentless march towards the other extreme of winter solstice when the sun touches the zenith along the Tropic of Capricorn. In June the sun strode over the Tropic of Cancer, 23.5 degrees north of the equator. Now it is on the equator, and six months from now, Sol will be over the Tropic of Capricorn at 23.5 degrees south latitude. That is a 47 degree change in the position of the sun over the course of a year, a condition attributable to the 23.5 degree axial tilt of our planet’s axis to the perpendicular of its orbital plane. So say goodbye to summer and hello to fall, and just for the record, I’m not looking forward to the winter’s snows.

840    SEPTEMBER 23, 2012:   Sundogs, Halos Herald Autumn

Driving home from church on the ides of September, my wife, Susan, and I were greeted by the sight of an incredibly bright sundog to the left of a nearly setting sun. A friend of mine, Willard Clewell, had once remarked that he had seen a sundog that was so intense that it was hard to view. The brightness of this apparition, as in Clewell’s description, made me want to turn away, even through it would not have caused any eye damage. Sundogs and halos will become more common as we head into the autumn and winter months because they are not the result of sunlight being refracted through raindrops, like a rainbow, but rather light being bent inside hexagonally (pencil) shaped ice crystals. Indeed the deeply saturated lapis sky of September 15 was filled with high altitude, wispy cirrus clouds which were perfect for creating these effects. When sunlight enters a tiny ice crystal, there is a concentration of light refracted at an angle of 22 degrees, causing sundogs which are bright rainbow colored spots in the sky, and halos which appear to surround the sun, to begin their visibility at this angle from Sol. Whether or not a dog or halo is seen depends solely upon the length and orientation of the ice crystals. Halos represent a random orientation of long hexagonal crystals so that everywhere in the sky there are some crystals at the proper position to refract light back to the eye. Sundogs are different. Here, the hexagonal crystals are like plates, still six-sided but not very thick. These crystals fall through the air like leaves from a tree keeping an orientation which is essentially parallel to the ground. Because all or most of the ice crystals are positioned in the same manner, they refract light back to the eye in only one direction causing bright spots called sundogs to become visible at 22 degrees on either side of a low sun. Luckily, I had my camera. A picture of my sundog is posted online at the URL below.

Surprise Photo:   On September 15, when I imaged this sundog, the bright spectral patch of light left of center in the photo, I was unaware of the sun pillar visible as the faint, narrow pinkish shaft of light above the sun. This was my first sun pillar photograph. To form this pillar, reflection occurred from the bottom plates of thin hexagonal ice crystals, falling like leaves in the atmopshere and nearly parallel to each other and the ground. Note the lack of spectral detail in the pillar indicating reflection and the reddish color which is characteristic of a very low sun. Photo by Gary A. Becker near Center Valley, PA...

841    SEPTEMBER 30, 2012:   Fun Views Inaugurate October

If you like watching sunsets, the next seven days offer the causal observer an opportunity to witness how fast the pace of nature can progress. You’ll note a 10 minute difference in sundown times from the beginning to the week’s end, a 16 minute decrease in the time of daylight if sunrises are also taken into consideration. Early in the week after sunset, notice the nearly full moon low in the east illuminating the landscape during late twilight. This past full moon (Saturday at 10 p.m., EDT) was the Harvest Moon, when farmers, especially in Europe, would continue to use the light of a bright moon to prolong harvesting activities well past sundown. This is also a good week for astronomical events if your waking hours are more inclined to an early rise time. The year’s closest appulse of a planet and a bright star happens on the morning of the third. An appulse is simply a close approach of one celestial body to another. In this case it is the intensely bright Venus right next to the first magnitude star Regulus in the constellation of Leo the Lion. From the East Coast the pair is separated by just nine minutes of arc at 5 a.m. Venus will be over 150 times brighter than Regulus. This might make the alpha star of Leo difficult to spot with the unaided eye in the glare of Venus. Use binoculars to help separate the two and allow for their easier inspection. Employ a small to medium aperture telescope to witness the gibbous or bulbous phase of Venus next to this bright star. While you are gawking at the appulse, and maybe even applauding, take note of bright Jupiter to the left of the gibbous moon. Another close pairing is ramping up for Friday. Midnight on Friday finds the moon about four degrees distant from Jupiter. Look east. If you choose a dawn sighting (5:30 a.m., Oct. 6), the pair will be farther apart, but you’ll have the winter constellations adding their glitter to the morning sky.