StarWatch for the greater Lehigh Valley

APRIL  2007


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

[Moon Phases]
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554    APRIL 1, 2007:   The Moon's Many Motions
The moon dominates the evening sky during early April. The motion of our only natural satellite in concert with Earth’s orbital motion and the gravitational forces acting on the moon by our planet and the sun, create an extremely complex lunar dance that was not fully understood until the eighteenth century. Consider the fact that the moon orbits or revolves around the Earth in 27.32 days (sidereal month), but its phases repeat in varying cycles which average 29.53 days in length (synodic month). Because the Earth is in motion around the sun, it takes an additional 2.17 days beyond the moon’s orbital period before it is once again in its same phase alignment. The moon’s orbital plane is tilted just over five degrees to the plane of Earth’s orbit, the ecliptic, causing the moon on average to spend equal durations of time above and below this plane. The points of intersection of the moon’s orbit with the ecliptic are called its nodes. They are not stationary but move towards the west in a wobbling fashion like the lid of a large tin can quivering on a tabletop. Each wiggle takes 18.61 years to complete, sliding the two nodes westward, around the heavens during this time. Two successive crossings of the same node, called the nodical month, takes 27.21 days, a time interval 1/10-day shorter than the orbital period of the moon. Finally, there is the lunar anomalistic month of 27.55 days. As the moon swings around the Earth, its oval-shaped orbit brings it closest to our planet at a position called perigee, and farthest from our planet at a location named apogee. The connector between these two points is the line of apsides which shifts eastward around the sky in a period of 8.85 years. This moves to the east the location in the sky where we observe perigee and apogee. Confused? So are some of my astronomy students!

[Sidereal-Synodic Months Explained]
The many motions of the moon yield a variety of lunar months. Above, the revolution (sidereal) and phase period (synodic) of the moon are explained. Below, the nodical and anomalistic months are diagramed. The synodic, nodical, and anomalistic months are important in explaining the repetition of solar and lunar eclipses. All graphic by Gary A. Becker...

[Nodical Month]

[Anomalistic Month]

555    APRIL 8, 2007:   Front Yard Safari
The aspect about teaching which I hate the most is the jangle of my alarm ringing at 5:45 each weekday morning. Going through my sunrise ablutions, I usually pop outside just before 6 a.m. to go on safari, hunting down the morning paper which can be situated anywhere within a thousand square foot area, but lately has been found just beyond my reach underneath my Saturn SUV. I have barely resisted stealing one of my neighbors’ papers which always seems to roll to a precise resting place in the center of their driveways. The positive side of this early dawn scavenger hunt is that I get to see the sky way out of joint from the current season. Presently at dawn, the heavens have a mid-August look, minus, of course, the positions of the moon and planets. If you are also outside at dawn hunting for your newspaper, you’ll notice the waning moon dominating the southern sky this week. It progresses from a gibbous phase, more than half lit, to a horned crescent by the week’s end. The very conspicuous star like object low in the south is the planet Jupiter. I have been watching it for months as it has gained greater prominence peeking in and out of the skeletal branches of my neighbor’s trees. Just below and to Jupiter’s right is Antares, the red supergiant star of Scorpius the scorpion. I have a distinct advantage here because I must vector south from my front door towards the driveway to look for the paper. Upon retrieving it and turning around, I am now facing north and viewing the Big Dipper, low in the NE, cup down and handle up, as well as the Great Summer Triangle nearly overhead and to my right. Okay, maybe there are some meager advantages of an early morning wakeup call, but could my newspaper carrier kindly stop playing hoops with the undercarriage of my Saturn?

[A Good Throw]
And this was a good throw... Seriously, it doesn't happen that often, but occasionally my morning paper gets thrown underneath my car and rolls to an unreachable position. Photo by Gary A. Becker...

556    APRIL 15, 2007:   Catch a Falling Star This Weekend
This coming Sunday morning marks the beginning of the spring meteor season with the peaking of the Lyrids, shooting stars that at maximum activity produce on average about 18 events per hour. This is certainly not a barnburner of a meteor shower, but compared to the dearth of activity during the previous three months, it is absolute bliss. Meteor observing is a great way to get started in astronomy. All you need is average eyesight and a reasonably dark location from which to observe. As a young teen growing up in Allentown, enjoying astronomy on a weekly allowance of 50 cents was not exactly conducive to buying expensive equipment. I could afford a sleeping bag, and I could drag the chaise lounge chair that my dad had built with its soft cushy mattress to a place in the backyard where I had a reasonable view of the sky and look for meteors. More importantly, by watching for those bits and pieces of dirt dislodged by comets lighting up the atmosphere, I became very familiar with the night sky. In my late teens, I thought it might be cool to survey the sky during the meteor slow season. One very clear and bitter February night, I stayed out for three hours without catching a single shooting star. In February 2001 when I spent three weeks at Siding Spring, Australia’s national observatory, I probably saw less than 10 meteors. One of them, however, I caught on film. So you might see how a meteor enthusiast’s heart might pump just a little faster with the possibility of seeing five or 10 meteors per hour. If you want to catch a Lyrid, make sure you’re out about 4:00 a.m. Sunday. Focus your attention on that bright star nearly overhead. That’s Vega, in the constellation of Lyra the harp. If a meteor seems to zip away from that region of the sky, chances are good that you snagged a Lyrid meteor.

557    APRIL 22, 2007:   "Contact"
When time and scheduling permit, I like to show my astronomy students the movie Contact. It’s not your typical alien film where humanity battles back from the brink of extinction, outwitting a technologically superior enemy, such as Independence Day or War of the Worlds portrays. Directed by Robert Zemeckis, Contact’s well-crafted 150 minutes pits feisty radio astronomer and atheist, Ellie Arroway (Jodie Foster) against religious scholar and eye candy hunk, Palmer Joss (Matthew McConaughey). Based upon astronomer Carl Sagan’s fictional work by the same title, this is one instance where the film translation is superior. Contact is not exactly a teenager’s top choice in cinematic entertainment, but when my classes view the film, they are made to consider the fundamental differences between science and religion and the fact that they can co-exist and mutually aid one another in the quest for truth. When we finally make contact with an alien culture, it probably won’t happen with a handshake, but rather as the movie portrays through a message carried on the wings of radio energy and intercepted by a radio telescope. Contact’s author, Carl Sagan, was an atheist who believed that humanity was at the brink of truly great achievements or self-annihilation. Through Ellie and Palmer the viewer can gain insights into Sagan’s own struggles with spirituality and the human condition as he neared the end of his life. Sagan never saw his movie to completion. Perhaps even more poignant was the question asked by Allen senior, Chris Sanchez, who recently came to the Lehigh Valley via the Bronx. “May I have permission to cry? This movie always makes me cry.” I nodded yes, telling him that his tears of hope would be shared by at least one other individual in the room.


558    APRIL 29, 2007:   I Blew It in Bluff
I blew it in Bluff when I followed three pickups into this sleepy Utah town. Within moments the faded stucco buildings were behind me and so was a cruiser with its flashers pulsing. I remember saying to my buddy Allen, “Do you think that’s for us?” “Just keep driving,” he mused. So I did, and one by one the trucks pulled off the highway onto narrow dusty roads leaving us, and another screaming cruiser coming up from behind. “Ooooh (you fill in the word),” I said, coming to a halt. An agitated Navajo police officer approached. “Do you want to spend a night in jail?” At the conclusion of his heated oratory, Allen and I found ourselves returning to Bluff with a $25 summons, more cash than I usually spent in a day’s worth of traveling. The JP met us at the door with a friendly hello. He was in a wheelchair. I’ll call him Ironside. It was obvious that he wanted to talk, so we complied, and within moments he knew that we both worked in planetariums. “Boys, have you ever heard of one of those small telescopes called a Questar?” Ironside queried. I smiled broadly and said, “YES, I just happen to have one in my trunk.” Questar is the Cadillac of portable telescopes. I call mine an observatory in a shoebox, and had purchased a used model as a college graduation gift in 1972. It still goes along with me whenever I travel. The next three hours were spent showing Ironside just how a Questar worked and in receiving a VIP tour of his home, which was a marvel of innovations, many of Ironside’s own design, which allowed him to be a self-sufficient individual, even though confined to a wheelchair. Keep in mind that this was 1976, long before the Americans with Disabilities Act of 1990. Ironside reduced our citation to $12.50, and we left with smiles, ready for our next encounter with the law the following morning.

[April Star Map]

[April Moon Phase Calendar]