StarWatch: Moravian College Astronomy

StarWatch for the greater Lehigh Valley

MARCH 2013

MARCH STAR MAP | MOON PHASE CALENDAR | STARWATCH INDEX | NIGHT SKY NOTEBOOK

Print Large Sky Charts For 9 p.m. EDT: NORTH | EAST | SOUTH | WEST | ZENITH

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Current Moon Phase

863 MARCH 3, 2013: Drinking Gourd on the Rise: If you go outside about 8 p.m. and look towards the NE, you’ll notice the familiar pattern of the Big Dipper, beginning its springtime ascent, handle down—cup up, rising above the tree line of your local neighborhood. The bright moon may hamper seeing its seven stars at the beginning of the week, but by week’s end, Luna will be gone from the early evening sky. The Dipper is purely American, not even a constellation, possibly originating from the Drinking Gourd song taught to slaves by itinerant carpenter and abolitionist, Peg Leg Joe. Its lyrics gave slaves in Mississippi and Alabama, where Joe worked, a coded message to follow the Tombigbee and Tennessee rivers to the Ohio River, and across it to Illinois and their freedom. The song began with, “When the sun comes back, and the first quail calls” which signified mating season and starting the journey during the spring. It told slaves, “The riverbank will make a mighty good road, /the dead trees show you the way” with markings of Joe’s “left foot, peg foot,” indicating that they were on the correct route. Every verse ended with “Follow the Drinking Gourd,” which always kept people in a general northbound direction. At the headwaters of the Tombigbee, “between two hills, /There’s another river on the other side,” the Tennessee. So “Follow the Drinking Gourd.” And “When the great big river (Ohio) meets the little river (Tennessee), /Follow the Drinking Gourd.” The dangerous trip along the hundreds of miles of snaking riverbanks, took escapees about a year to traverse, bringing them to the Ohio, hopefully, when it was frozen and easier to cross. Newer interpretations of the Drinking Gourd song say that it is all folklore, but even in a tale there is usually an element of truth. For “the old man is awaiting for to carry you to freedom, /If you follow the Drinking Gourd.” That was written 80 years after the Civil War’s end.

864 MARCH 10, 2013: Comet in the West: I have been waiting several months for this week to arrive because currently there is a comet on the western horizon after sundown. As this article is being written, it has become an easy target to view with the unaided eye from the Southern Hemisphere. It even has a short tail. Now it’s headed north for us to see. The interloper’s name, PanSTARRS (C2011 L4) comes from the Panoramic Survey Telescope & Rapid Response System, its goal to discover Earth-crossing objects like the meteorite that fell in Russia on February 5. Oops! Actually, no doomsday detection system will be able to discover something that small. PanSTARRS reaches its closest distance from the sun on March 10, just inside the orbit of Mercury, where hopefully solar radiation will sublimate vast quantities of its ices and release copious amounts of dust into space. These are the ingredients that make for a bright comet. The gases glow through a process called fluorescence, while the dust scatters sunlight back in our direction. If there is enough dross, the comet could shine as brightly as the brightest luminary of the night, Sirius, the Dog Star of Canis Major. It should also have a noticeable tail, especially through binoculars. PanSTARRS was becoming brighter as predicated up through December 2012, but since the New Year, the brightening has slowed. Now with its easy views from Down Under, its final brightness may again be up for grabs. Comet PanSTARRS will be low to the western horizon, about eight degrees in altitude, 45 minutes after sundown during the next two weeks. It will be a deep twilight apparition. Very clear skies and a flawless western horizon will be necessary ingredients for a successful observation. If the comet is bright, you’ll hear more about PanSTARRS next week. Keep in mind that comets are like cats. They have tails, and they do precisely as they please.

865 MARCH 17, 2013: Tricky Comet PanSTARRS: Where is Comet PanSTARRS? I was asking myself that question for the last four days, and with the bad weather veiling the Northeast, I thought that maybe the comet was simply going to be a lost cause. Then with nearly overcast skies on Wednesday, March 13, and snowflakes flying in the air, I thought that I’d take a chance and schlep my photographic gear to one of my favorite haunts in the hopes that it would clear. There was a snow shower approaching; I could see darker virga, wisps of precipitation evaporating before reaching the ground, silhouetted against the brighter clouds. There was also a lighter band of clearing sky just along the western horizon, and from the direction of the wind, that band would get larger. Would the comet set before it cleared or would I get my first peek at PanSTARRS? I was lucky. It snowed for about 15 long minutes, then the strip of clearing sky rapidly expanded to about 10 degrees. I scanned the western horizon with binoculars, and there it was, an easy view with a small arched tail, probably no more than a half degree. Photographically, it was a much different beast, very prominent against a bright sky and with a tail extending just over three degrees. My March 13 image can be seen at www.astronomy.org. Click on “this week’s StarWatch.” If Comet PanSTARRS was higher and seen against a darker sky, it would be a very easy naked eye target and absolutely spectacular through a small telescope. Its low altitude makes it nearly impossible to see with the unaided eye from light polluted areas, but it presents a very nice sight through binoculars. During the next several weeks PanSTARRS will get slightly higher in the sky, but its orbit will preclude it from becoming more than a dozen degrees above the western horizon. Use binoculars. Make sure your west is unobscured. View around 8 p.m. Be patient. PanSTARRS will be there.

866 MARCH 24, 2013: Full Moon Watch: March 29 is the day of the full moon, and although regular sky watching is usually at a minimum, the moon is there for the taking. Full moons, however, are not good times to use a telescope. Lack of shadow detail will produce bland, disappointing scenery at high powers, but views of the moon through binoculars or with the unaided eye will not disappoint. First noticed are humongous darker circular features on Luna. These are the maria or the seas of the moon. Seventeenth century observers thought that they were basins filled with water. They got the “basin” part correct, but water has always been a sparse commodity on the lunar surface. They were actually made by large meteorite impacts about 3.85 billion years ago at a time when something went amiss in the solar system. Perhaps it was the beginning of the grinding down process which shaped the asteroid belt between Mars and Jupiter. These craters, after about 300 million years, began to fill with lava which pushed its way from the warmer interior through the fractures created by the impacts. The composition was slightly different, allowing for less reflectivity in these areas, revealing them as darker features. The rest of the moon’s near side appears whitish, a condition caused by the ceaseless pulverization of its surface by meteorites that have stuck the moon during its 4.5 billion year history. These areas called terra or the highlands are the original regions of the moon to turn solid after its genesis. Splash marks associated with brighter craters can also be seen dotting the lunar landscape. These are fresh impact sites, probably less than a billion years old. As an airless astronomical body like the moon ages, it picks up bits and pieces of meteoric dirt, causing its surface to darken. Larger meteorite impacts have gardened Luna, exposing fresher, brighter material which is best seen around the full moon.

867 MARCH 31, 2013: Comet ISON: No April Fools' Joke: While much deserved attention has been focused on Comet PanSTARRS during the last three weeks, another hairy interloper is sun bound for an autumn rendezvous with Sol. ISON (C/2012 S1) could be one of the great comets of all times, and this is not an April Fools’ joke. First imaged by two Russian amateur astronomers, Vitali Nevski and Artyom Novichonok, on September 21, 2012, ISON was named for the telescope of the International Scientific Optical Network that took the discovery photograph. There are several criteria which make Comet ISON noteworthy. It is classified as a “sungrazer.” When it makes its closest approach to the sun on Thanksgiving Day, Nov. 28, 2013, it will be a scant 1.1 million miles from Sol’s light-emitting surface, and well within its multimillion degree corona. The physical processes which create the tail structures of comets will literally be “on steroids” during the pre- and post perihelion days and could produce a spectacle visible from the largest cities in the Northern Hemisphere. On the other hand, the heat and gravitational disruptions which ISON will experience during its close solar encounter could simply make it go puff, creating unprecedented space photos, but literally nothing of importance to see for Earth’s inhabitants. The other interesting consideration is that ISON is following an orbit which is very similar to the Great Comet of 1680. This comet, visible during daylight as it rounded the sun, produced a bright tail of some 70 degrees in length as witnessed by Dutch settlers living on Manhattan Island in New Amsterdam during the late autumn of 1680. ISON will probably not shine that brightly, but should it survive its close passage around the sun, it will become one of the great popular astronomical events of the 21st century. Photos representative of the appearance of Comet ISON may be found at www.astronomy.org/StarWatch/March/index-3-13.html#3-31-13.

[March Star Map]

[March Moon Phase Calendar]