StarWatch for the greater Lehigh Valley

APRIL  2006


Print Large Sky Charts For 10 p.m. EDT:   NORTH | EAST | SOUTH | WEST | ZENITH

[Moon Phases]
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Status Current Moon Phase

502    APRIL 2, 2006:   New Horizons Sending Tombaugh Home
When Clyde W. Tombaugh made his amazing discovery of Pluto in 1930, little did he expect that one day he would get the opportunity to fly past this tiny, isolated world. In fact, he is on his way right now. Tombaugh, an amateur astronomer born in Streator, Illinois was hired by the Lowell Observatory in Flagstaff, Arizona to conduct a search for a Planet-X. Tombaugh’s superb drawings of Jupiter and Mars made from his parent’s wheat farm in western Kansas with a homemade 9-inch reflector convinced Lowell Director, V. M. Slipher, to hire Tombaugh as the observer for the search. By giving a qualified amateur a chance, Slipher believed that Tombaugh would stick with the difficult and tedious observing routine that the search required. It was a wise decision. Tombaugh not only took over the project, but he greatly enhanced the observing and analysis techniques which led to a speedy identification of his trans-Neptunian world. The moment of discovery occurred on February 18, 1930 “within about two minutes of four p.m.” in Tombaugh’s own words. Currently, NASA’s New Horizons is headed towards Pluto after a successful January 19 launch. Several years before his death in 1997, NASA asked Tombaugh, as a courtesy, for his permission to send a probe to icy Pluto. Of course, he said, “Yes!” New Horizons will get a gravity assist from Jupiter in February 2007 to slingshot it to Pluto. Then there will be an eight year hiatus as the small spacecraft hunkers down and cruises towards Pluto and its three moons for a July 2015 rendezvous. All the while, a small compartment containing 70 grams of Clyde W. Tombaugh’s cremated remains will be making the journey, back home to Pluto where Tombaugh’s legacy began three quarters of a century ago.

503    APRIL 9, 2006:   Does the Moon Rotate?
“Does the moon rotate?” A look of quiet desperation ripples through my classroom. Eye contact rapidly dissolves. I know what my students are thinking. He’s using the “R” word again. Does rotation mean to spin or to orbit? “How long does it take the Earth to complete one rotation on its axis?” I quip. Voices robotically react with 23 hours, 56 minutes, 4 seconds. “Almost a day,” I respond. Okay, what he’s really saying is, does the moon spin on its axis? About 80 percent of the class says “no.” The “yes” pupils can’t explain why they’ve said “yes,” but the “no” people insist that the moon cannot possibly spin because it keeps its same “face” perpetually glued towards the Earth. I now close the classroom door to eliminate embarrassing stares generated from hallway traffic, and my students stand. “Complete one rotation with your eyes open,” I demand in my best commando voice. Most of my students comply. “All four walls of the room were visible while you completed your spin,” I retort. Weary voices respond, “Yes.” “Pick a partner,” I continue. “One of you will become the Earth while the other is the moon. Keeping your faces towards Earth, moons will revolve (orbit) around their Earths while noticing the walls at all times. If the moon is rotating (spinning) while it is revolving (orbiting), then you should see the walls changing.” The demonstration is completed and then roles are reversed. All four walls are seen. My pupils recognize that because the moon keeps its same face pointing towards the Earth actually proves that the moon rotates. The moon orbits the Earth and rotates on its axis in precisely the same period, 27.3 days, a synchronous motion. The bell rings. For the moment, another misconception bites the dust. The moon is full on Thursday.

[Does the Moon Rotate?]
The moon rotates because it keeps its same hemisphere pointed towards Earth. The open end of the “Y” faces all four directions—completes one rotation about its axis—as the moon completes one revolution, or orbit around the Earth. Drawing created by Gary A. Becker...

504    APRIL 16, 2006:   Lyrid Meteors Now!
The general kickoff of the meteor season begins with the Lyrids, shooting stars that radiate near the blue-white luminary Vega in the summer constellation of Lyra, the Harp. On Saturday morning they will be at their peak. Meteor showers almost always have an association with the dross released by comets, and for the Lyrids, it is the 415 year period Comet Thatcher, discovered in 1861, that is the culprit. This year, North America is ground zero for viewing this event. Not only is the moon in a cooperative phase, a waning crescent, two days past third quarter and rising around 2:45 a.m., but the peak shower activity for North America happens at 4:30 a.m. EDT, when the star Vega is nearing the zenith for East Coast viewers. Conditions could not get much better for seeing these meteors. The downside to the Lyrids is that rates are relatively low, about 10 shooting stars per hour, although outbursts have occurred in which meteors were seen in the hundreds per hour. Lyrid meteors will be visible all week, but conveniently, the best time to watch will be on Saturday morning between midnight and dawn. Make sure you are dressed for winter-like conditions. Ground mats, reclining lawn chairs, sleeping bags, pillows, and warm caffeinated drinks are all part of staying comfortable and alert while waiting for a meteor to flash. Face your body towards the east and observe straight overhead. If you are out around midnight, Vega will be the brightest star in the NE. Don’t confuse it for brilliant Jupiter in the SE. By 4 a.m., Vega will be high in the east headed towards the zenith and in the darkest part of the sky. When a Lyrid flashes, its luminous trail created by a tube of glowing air about one mile in diameter, will trace itself back to a position just to the right of Vega. Good observing!

505    APRIL 23, 2006:   Surprise Comet--Maybe
I always like surprises and there may be one headed our way in the form of Comet 73P/Schwassmann-Wachmann 3. Now that’s a mouthful. You might get the idea that S-W3 has a connection with Germany. Indeed the discoverers, Arnold Schwassmann and Arno Arthur Wachmann were two German astronomers conducting a photographic survey of asteroids, when they serendipitously discovered the comet on May 2, 1930. S-W3 is a short period comet, rounding the sun every 5.36 years. The location of the Earth with respect to the comet can make all of the difference between S-W3 being a binocular object as it was in 1930, or not being seen at all. In fact, after its 1930 discovery with Schwassmann-Wachmann 3 passing within six million miles of the Earth, the comet was not recovered again until 1979. Three orbits later in 1995, with S-W3 faint because of its 122 million mile distance from the Earth, the comet unexpectedly brightened nearly 1000 times, becoming a binocular target like it was in 1930. Several months later, astronomers noticed that S-W3 had split into four distinct parts. The brightening resulted from an increased surface area and new, fresh volatiles being exposed for the first time to the eroding effects of sunlight. During this apparition, S-W3 will pass the Earth on May 13 at a scant seven million miles, similar to its discovery distance. Unfortunately, May 13 is also the night of the full moon—SCREAM—which will make the comet difficult to see. The week of May 7, about two hours before sunrise, will probably provide enthusiasts with the best opportunity for seeing S-W3. During that time the comet will pass through the constellations of Hercules, Lyra, and Cygnus. See the online map posted with this StarWatch at the URL below.

[Comet 73P/Schwassmann-Wachmann]
How bright will Comet Schwassmann-Wachmann shine?  It certainly will not be as bright as in the map above. More likely S-W3 will appear large, about the diameter of the moon, and looking more like a faint cotton ball through binoculars. The map above will give locations for S-W3 during the time period when it should be brightest. After May 12, the comet will become more difficult to view because of moonlight. The bright star Vega, in Lyra the Harp, is nearly overhead by 4 a.m. Map created by Gary A. Becker...

506    APRIL 30, 2006:   Jupiter Returns to the Evening Sky
Jupiter will finally reach opposition this Thursday, meaning that it will be opposite to the sun, rising at sunset and setting at sunrise. Recently, the largest planet of the official nine has been the dominating “star” brightening the southeastern sky before midnight. A few months back, Jupiter, low in the southwest, was piquing the interests of early morning risers. After opposition, Jove passes from a morning to an evening planet, setting before sunrise, but rising about four minutes earlier each day. By June 21, the date of summer solstice, Jupiter will be low in the south, becoming visible in bright twilight after sundown. Come late summer, Jupiter’s brilliance will succumb in the southwest during evening twilight. Why such a short display of prominence for the mightiest of all planets? It has to do with Jupiter’s position along the ecliptic, the path across the sky through which the sun traverses in response to Earth’s annual circuit around our daystar. The placement of Jupiter in the sky is currently at the location of the sun in early November, and everyone knows how short the days are becoming by that time of the year. With the sun approaching summer solstice, the nights shrink to what the lengths of the days will become six months into the future. So Jupiter’s glory days will be short. The most positive aspect of a late spring or summer opposition is the comfort factor. You won’t have to layer yourself in 15 snowsuits to maintain some degree of warmth while observing Jupiter through a telescope or binoculars. Summer nights also produce less turbulent air which provides some compensation for the lower altitude of Jupiter and the longer air path through which telescopes must peer. Give Jupiter the “once over” during the next month. You won’t be disappointed.

April Star Map

April Moon Phase Calendar