StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

JANUARY 2007

JANUARY STAR MAP | STARWATCH INDEX | MOON PHASE CALENDAR

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542 JANUARY 7, 2007: Auriga: Auriga the Charioteer is now positioned high in the east by 7:00 p.m., a sure sign that winter, at least astronomically, is upon us. Dazzling is Auriga’s Capella, the sixth brightest luminary of the night. Its color and brightness would be similar to our sun’s appearance at a distance of 3.7 light years (ly), not quite as far away as the Alpha Centauri system which contains Proxima, our closest stellar neighbor. Capella, however, is 42 ly away which means it is a more luminous star. This can mean only one thing; Capella is much larger than our sun. In fact, Capella isn’t even one star. It is a (spectroscopic) binary composed of two aging, giant stars that revolve around each other in a period of 104 days. The other luminaries of Auriga are similar in brightness to the stars of the Big Dipper, making for what I believe is a very conspicuous chariot. Most observers do not agree with me. Go online at the URL below and then click on “this week’s StarWatch” to view a map of Auriga and see how I conceive the chariot. Near the wheel of Auriga are three galactic or open clusters which are visible through binoculars from suburban and rural areas: M36 (4,100 ly distant), M37 (4,600 ly), and M38 (4,200 ly). They were first seen telescopically by Giovanni B. Hodierna (1597-1660) of Ragusa, Sicily. These clusters represent groups of stars which were born at the same time from nebular clouds of gas and dust, similar to the best example of its kind, the Pleiades, which are nearby in Taurus the Bull. The Auriga clusters are older and much farther away. The brightest and showiest of the trio is M37, but the other two are almost as bright. When I was at Siding Spring, Australia’s National Observatory in 2001, these three clusters were visible to the unaided eye. What a magnificent sight!

543 JANUARY 14, 2007: Volcanic Enceladus: If I take two iron spheres, one baseball-sized and the other volleyball-sized, and heat them to an equal temperature, which one will cool faster? If you’re thinking about the baseball, you’re correct. Its surface area to volume ratio is about three times greater than the volleyball, and therefore under similar conditions, it must lose heat faster. Likewise, when the planets were forming nearly five billion years ago, their surface area to volume ratios helped define how fast they would cool. Earth’s central core temperature is 11,000 deg. F. Jupiter, the largest planet in the solar system, has a core temperature in excess of 50,000 deg. F. So what would you expect of a 323 mile in diameter satellite orbiting Saturn? It must have cooled very rapidly and at present, be frigid from its surface to its core. Right…? Wrong…! Welcome to the wacky world of Enceladus, the newest member of the Solar System’s Volcano Club. Icy Enceladus, with a daytime surface temperature of -320 deg. F., has geysers near its south pole. Heated water moves towards the surface of Enceladus and meets a pool of cooler water that is percolating into the same large chamber. The cooler water acts like a lid or pressure valve, trapping the warmer water and steam. Pressure builds until it is great enough to blow out the layer of cooler water from a weak zone or fracture in the crust. The lower pressure allows for the rapid generation of more steam which continues the eruption. Geysers on Enceladus operate at much lower temperatures than Earth geysers because Enceladus possesses less surface gravity and virtually no atmosphere. Some of the erupting geyser ices escape Enceladus’s low gravitational field to repopulate the ephemeral E-ring which encircles Saturn. Photos are posted at the URL below.

544 JANUARY 21, 2007: Venus and Mercury on the Rise: As winter begins to take its first nasty bite in the northeast and continues its grip throughout the western half of the country, two planets, Mercury and Venus, are emerging from the sun’s glare in the cold evening twilights. Venus has been around since Christmas, but until last week observers had to discern it against a fairly bright sky. This week by 5:45 p.m., about a half hour after sunset, Venus will be an easy target low in the WSW. By 6:00 p.m. as the sky becomes even darker, Venus will be conspicuous to drivers in rush hour traffic if western horizons are not obscured by buildings or trees. Viewing Venus will only become better throughout the spring as the Goddess of Love pulls farther away from the sun and can be seen in a completely dark sky. Look for Venus to dominate the western heavens until early July. Also not to be forgotten is Mercury, which will begin to make an appearance below Venus by the end of this week. Although Venus will be nearly 15 times brighter than Mercury, the Messenger God will still rank as one of the brightest objects in the twilight sky. Only Sirius the Dog Star, low in the southeast during the early evening hours, and the moon, trekking from above Venus on Sunday to above Orion the Hunter by week’s end, are brighter. Begin your search for Mercury nearer to the end of the week. Clear skies and a good southwestern horizon are mandatory. Use binoculars, and start observing about 30 minutes after sundown. Scan the heavens between Venus and the brightest part of the horizon. Any star like object found along this path will have to be Mercury. During the following week Mercury will be higher in the sky as it moves farther from the sun and a little closer to Venus. Look for an ultra thin crescent moon to be located between Venus and Mercury on February 18.

545 JANUARY 28, 2007: A Wild and Untamed Landscape: With the moon waxing towards its full phase late this week, an excellent opportunity exists for viewing its cratered landscape. Lunar craters come in all sizes, from the miniscule impacts made by micrometeorites to the dark, lava-filled circular basins or lowlands which are easily viewed by the unaided eye. The larger impacts, created by meteorites which strike the moon at space velocities, have certain characteristics. Crater walls are always higher than the surrounding terrain while crater floors are always lower than the neighboring landscape. A curious aspect of many large impacts is a central peak or a mountain in the middle of the crater. When a meteorite several miles in diameter hits a large solid body, ground zero acts very much like a liquid. Throw a rock into water and a splash results, as well as ripples emanating from the target zone. Moments after the impact, the meteorite is vaporized. The ground which was compressed and crushed may rebound to become the permanent splash of a central peak. Rock strata from the crater floor are overturned, thrusting upward the walls and propelling huge amounts of debris outward to bombard the surrounding landscape with a peppering of secondary craters, slash marks, and arcuate patterns that surround newer impacts. Debris that is propelled even farther rakes or gardens the ground, exposing fresher, lighter soil and forming the bright ray systems that can radiate for many hundreds of miles away from the impact. Seismic ripples from the meteorite shock may weaken and fault the crater walls which can later collapse producing a terraced or stepped effect. Observe crater rays near full moon and crater detail along the terminator where day merges into night. The moon is a wild and untamed landscape begging to be viewed with even the smallest of telescopes.

January Star Map

January Moon Phase Calendar