JULY  2012

JULY STAR MAP | STARWATCH INDEX | MOON PHASE CALENDAR

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828    JULY 1, 2012:   Hot Summer, Distant Sun

We’ve passed the longest day of the year, the summer solstice, where Sol reached its highest place in the sky for residents on or north of the Tropic of Cancer. Although it’s all downhill until the winter solstice, there is obviously plenty of summer still left to enjoy, and it isn’t all due to global warming. One of the curiosities of the seasons in the Northern Hemisphere is that they are completely out of synch with the Earth’s distance from the sun. The common belief that summers are hotter because we are simply closer to the sun could not be further from the truth. In fact, this year the Earth reaches aphelion, its greatest distance from the sun, on July 4 at 11 p.m. So while we are reveling in flashy fireworks displays dressed in flip-flops, shorts, T’s, and tanks, Earth will be within one hour of its greatest distance from the sun. Earth’s axial tilt is the reason for the seasons. In summer the Northern Hemisphere leans towards the sun, placing the sun higher in the sky and allowing Sol’s energy to be more direct. The net effect is a greater amount of energy per unit area and warmer conditions. But because we are at a greater distance from the sun, Earth’s orbital speed is just a little slower, meaning that we get a few more days of spring and summer, when it’s warmer, than we do in the cold winter season when Earth’s orbital speed is faster. Other factors create an illusion of a longer summer. The solstices may represent the extremes in the length of the day, but they do not reflect the extremes in sunrise and sunset. The latest sunset occurred on June 27, which seems to prolong summer just a little bit longer. Who cared about the June 14 earliest sunrise because we were all in bed? Temperatures will max in late July, five weeks after the high sun; so as fall approaches, the Northern Hemisphere will still have plenty of heat in reserve to keep conditions comfy until late October.

This Milky Way image was taken by Matt Gustantino of Orefield, PA using the new Canon 60Da enhanced to record hydrogen emmision nebulae. The lavendar appearance of some of the "clouds" of the Milky Way confirm the increased hydrogen alpha sensitivity. The image was taken from Cherry Springs State Park in Potter County, PA.

829    JULY 8, 2012:   Rise and Shine: Venus, Jupiter Await

When I contemplate rising before dawn, I think of the Simpson’s episode entitled, “Bart’s Comet.” Bart Simpson discovers a doomsday interloper after pulling a prank on his science teacher, “Big Butt” Skinner. Bart’s punishment is to assist Skinner’s astronomy project, but Bart’s discovery steals the day. When the radio alarm wakes Bart at 4:00 a.m., the announcer is saying, “Top of the hour… Time for the morning news, but, of course, there is no news yet because everyone’s still asleep in their comfy, comfy beds. Good night everybody…” A confused and very groggy Bart bikes over to his school. I feel Bart’s pain when the alarm, or my mental alarm, awakens me from a deep sleep for an early morning star watch. Right now, that means rising at 4 a.m. and being quick about an exit into the cool, morning air, no more than 15 minutes later. Upon going outside you may still think that you are in the “twilight zone” because low in the ENE will be the same two brilliant objects, Venus and Jupiter, which graced the evening sky during the first half of this year. Now, however, the pair is on the morning side of the sun, with Jupiter higher in the sky than Venus. The entire week will produce superb views, but if there was one specific morning to highlight, I’d pick Sunday, July 15, because as the heavens brighten, a 13 percent lit, waning crescent moon will be straddling the pair. Jupiter and Venus will be less than seven degrees apart with the moon nearly in between. Because it will be a very thin horned moon, the portion of Luna not in direct sunlight should be resplendent with earthshine, light from a nearly full Earth reflected back to us by the moon. Wide-field binoculars will enhance the earthshine to help fuel the beauty of this conjunction which is also near the bright, orangey star Aldebaran in Taurus the Bull and below the Pleiades. I know I’ll be awake for this one.

The moon is nearly in between, Venus and Jupiter during early twilight on the morning of Sunday, July 15. In addition orangey Aldebaran and the ethereal Pleiades will join the scene. Binoculars will enhance the show but will be unable to capture all of the beauty in the same field of view. Illustration created using Software Bisque's "The Sky..."

830    JULY 15, 2012:   Cahokia's Woodhenge

Centuries before Columbus, a powerful culture rose on the floodplain of the Mississippi River. These people built a sophisticated city that became one of the great population centers in the Americas. During the 1100’s as many as 20,000 people lived here, rivaling the biggest cities of Europe. They influenced ways of life from the Great Lakes to the Gulf Coast, and made significant advances in astronomy, agriculture, and economics. By the fifteenth century the culture had essentially disappeared. This is Cahokia, located just east of St. Louis, MO, the largest archaeological site north of Mexico. It reminds me of a Mayan city with structures jutting upward from the surrounding, flat landscape. The scale is not as grand as Mexico, and unlike the Maya, who built from stone, the Mississippians used wood and soil for their edifices. Over the intervening centuries the wood rotted, leaving modern visitors to witness only the earthen mounds as they navigate the many pathways of the site. For me as an astronomy educator, it is Cahokia’s woodhenge that is most intriguing. There were at least five of them, built between 900 and 1100 AD. A center red cedar marker was surrounded by a ring of wooden cedar poles, with the number of markers in the ring varying by multiples of 12 between construction epochs. The largest ring had a diameter of 420 feet, but they all functioned in the same manner. Like Stonehenge, near the town of Salisbury, England, Cahokia’s wooden circles have been interpreted by archaeologists to be calendrical in nature, marking the times of high and low sun, the solstices, as well as the equinoxes. The number of circles built may have reflected the necessity of new construction as older ones deteriorated, or advances in concepts which led to more complex designs. Learn more about Cahokia Mounds at www.cahokiamounds.org.

The urban center of Cahokia flourished between 900 and 1200 AD. The site is located in Collinsville, Illinois off Interstates 55/70 and 255, just fifteen minutes east of St. Louis, Missouri. The picture above depicts the construction of the third woodhenge around 1000 AD, a circle which contained 48 poles and was used to mark the seasons. Below, can be seen the reconstructed third woodhenge, facing east towards Monks Mound, as it appears today. The sun rose on the equinoxes from the front of Monks Mound, the largest earthen structure at Cahokia (background right). Above: Artwork by Lloyd K. Townsend, Cahokia Mounds State Historic Site... Below: Photography by Gary A. Becker...

831    JULY 22, 2012:   Mars and Saturn Draw Near

Two weeks ago, I spoke about getting up at dawn to view Venus and Jupiter. They are still a beautiful sight in the eastern sky, playing brightly against the backdrop of Aldebaran and the Pleiades, but their separation continues to increase, 12 degrees by week’s end. If getting up at 4 a.m. is not part of your pressing agenda, then try another conjunction which is not quite as spectacular, but more suitable to normal waking hours. This gathering is unfolding at dusk in the western heavens near the horizon, and it involves Mars, Saturn, the star Spica, and this week, the moon. For many months Mars marched slowly in the constellation of Leo the Lion near Regulus, its brightest star, and Saturn in Virgo the Virgin near its principal luminary, Spica. Saturn, the slowpoke among the traditional planets as witnessed by the ancients, is still “hanging” above Spica, but Mars completed its retrograde (backwards) loop some time ago and has begun its normal rapid movement towards the east. This motion is bringing it closer and closer to Saturn and Spica. To make this conjunction even sweeter, the crescent moon enters the scene from July 23 through the 26th. On the 23rd, a horned moon will be below the pair; the 24th, nearer to Mars; the 25th, nearer to Saturn, and on the 26th, a slightly gibbous moon resides above the pair. Afterwards, Mars and Saturn keep approaching one another. By the first day in August, 45 minutes after sundown, the two planets are barely eight degrees apart. August 13 through the 15th finds them stacking like pancakes in the WSW at 9:00 p.m.—Saturn (top), Mars, and Spica (bottom). On these three nights, the separation between Saturn and Spica will be less than four and one half degrees, making them an ideal target to view through binoculars. By August 21st a thin crescent moon joins the triad for another very close encounter visible in the WSW during late twilight.

832    JULY 29, 2012:   Great Year for the Perseids

I always think of the meteor season beginning with the August Perseids. It is true that rates pick up somewhat after the Lyrid Meteor Shower which reach maximum on April 21, but it really does not become dramatic until the Perseids. This year, Perseid action is slated to be normal, but the moon is being more then cooperative. On the morning of maximum, August 13, when activity can approach one meteor per minute, Luna will rise as a thin waning crescent just after 2 a.m., a delicate ornament to the brightening dawn sky. The annals of Perseid activity go back for nearly two thousand years. The Chinese wrote about an abundant display of summer meteors in 36 AD, and references appear in early Japanese and Korean records, but it wasn’t until 1835 when the Belgium astronomer, mathematician, and sociologist, Adolphe Quetelet, brought the Perseids to the scrutiny of the scientific community. In the mid-1860’s, Giovanni Schiaparelli, the Italian astronomer who introduced the world to channels (canals) on the Martian surface, discovered that Perseid meteors orbited the sun in a similar path to periodic Comet Swift-Tuttle. Thus the association of meteors having parent bodies, mostly comets, but later also asteroids, was conceived. The summer Perseids are undoubtedly the most observed meteor event of the year. I have traveled several times to dark locations in New England and even as far west as New Mexico in 1994 to view them. When Swift-Tuttle made a return appearance in 1992, astronomers anticipated the Perseids might storm in 1994. Numbers were much higher than normal, but storm activity, rates of 1000 or more meteors per hour, failed to materialize. Sadly, my 11-day stay in the mountains north of Las Vegas, NM yielded only one clear period, but fortunately, that was the night of Perseid maximum. I’ll write more about observing the Perseids next week.