StarWatch for the greater Lehigh Valley

APRIL  1999

136    APRIL 4, 1999:   Eclipse Chasers Unite
Now that the clocks have been set ahead and the sun doesnít set until 7:30 p.m., many of us are going to begin contemplating summer vacation plans. If youíre considering a trip to Europe, try making your travel plans coincide with the 11th of August. One of natureís rarest events, a total eclipse of the sun, will be visible from both England and the European continent on that date. The moonís shadow first makes contact with the Earth at sunrise, about 325 miles east of Montauk Point, Long Island. People there, as well as individuals in the Lehigh Valley, will be able to observe a partial eclipse at sunrise with the proper filters. The path of totality continues northeastward reaching Landís End, in England during mid-morning, crosses the English Channel, and then passes about 20 miles north of Paris. The moonís shadow sweeps over Stuttgart and Munich, Germany, then Salzburg and Graz in Austria. Hungary, Bulgaria, and Romania also see totality before the moonís umbra crosses the Black Sea. The maximum duration in the shadow of the moon will be 2 minutes, 23 seconds. This occurs northwest of Bucharest, Romania just after 1 p.m. local time. Interested in seeing this eclipse? A local group of eclipse chasers have organized and are flying to Greece on August 2. After a day and a half in Athens they will set sail for exotic ports of call in the Aegean, and Black Sea. Totality will be viewed from aboard ship on the Black Sea on August 11. The 14 day odyssey will conclude with two days in Istanbul, Turkey. Follow the "í99 eclipse Black Sea" link at the web addresses below, or call the ASD Planetarium at 820-2204. To answer last week's question about when the moon was full; it happened on Wednesday, March 31 at 5:49 p.m.
137    APRIL 11, 1999:   What Time Is It?
We look at our watches, and our world is placed into an ordered framework from which we manage our affairs. Time has always been an astronomical problem based upon the spinning Earth and its ability to bring the sun back to a fixed position. But itís not quite that that simple. A properly working sundial takes its queues from the sun, registering noon when the sun is due south on the meridian. This is called apparent solar time. Each day, as Earth orbits the sun, Sol moves approximately one degree to the east against the fixed background of stars. But because our planetís orbit is oval-shaped, Earth travels faster in winter and slower in summer. This causes the sunís eastward motion to vary in a similar fashion, making the real sun cross the meridian ahead of or behind a fixed arbitrary beat of 24 hours. Enter mean solar time, which focuses upon a fictitious, uniformly moving sun which crosses the meridian in precise 24 hour increments. However, every location on the planet would have a slightly different mean solar time based upon its longitude east or west of the Prime Meridian. Allentown, Bethlehem, and Easton would have slightly different times because these cities are respectively eastward from one another. So we standardize mean solar time into zones to make scheduling more manageable. We further manipulate our clocks by jumping into the standard time zones to our east in summer to make the daylight hours more consistent with our waking hours. Does anyone know what time it really is? As you might have already guessed, there are many different answers.
138    APRIL 18, 1999:   Lyrid Meteors
The first major meteor shower of the year, the Lyrids, peak late Thursday into Friday morning. The moon will be at first quarter Thursday, and should have a minimal negative effect on the number of meteors seen. Meteor showers are generally named after the constellation from which the shooting stars are radiating. Meteors from the Lyrids, however, are actually emanating near the eastern boundary of Hercules, a region of the sky devoid of bright stars except for Vega, the principal star of Lyra, the harp. Blue white in luminescence, and the sixth brightest star of the nighttime sky, Vega lies only 8 degrees to the east of the radiant. It will be easy to spot by 11 p.m. in the northeast, about two fists above the horizon. Donít confuse it with reddish Mars which will be higher in the southeast and about five times brighter than Vega. Although observers are usually able to spot Lyrid meteors between April 16-25, concentrate your observations on Thursday morning, and especially Friday morning. Your best viewing window will be after 2 a.m. until dawn. By 3 a.m. Vega will be almost due east and more than half way up in the sky. Recline on a lawn chair for comfort and observe about one fist (held at armís length) to the right of Vega. That is the location from where the meteors will appear to be radiating. On Friday morning you can expect to see about 5-10 Lyrids per hour in suburban skies. However, in 1982 American observers recorded as many as 90 per hour. Donít expect rates like these in the Lehigh Valley, but sometimes the Lyrids do impress.
139    APRIL 25, 1999:   Blue Moon Enigma Solved
During the past several months this column has seen two articles about blue moons (see the Earth/Moon section in the StarWatch Index at the web site below). The term blue moon, meaning the second full moon of the month, seemed to have originated during the 20th century. Little else was certain. Now it appears as if our love affair with blue moons began as a mistake, some 53 years ago in "Sky and Telescope" magazine. The use of the blue moon was traced to the 1937 edition of the "Maine Farmersí Almanac." However, the blue moon date occurred on August 22, clearly not the second full moon of the month, since it takes 29.5 days for the moon to complete its cycle of phases. What happened? The "Maine Farmersí Almanac" used a seasonal scheme for determining blue moons based upon a uniformly moving sun which made the seasons of equal length. There were normally three full moons for each season, and each of these was given a name. When a season contained four full moons, the rule was to designate the third full moon of that particular season as the blue moon. This allowed the other three named full moons to occur in better step with the seasons. In other words, the blue moon to the "Maine Farmersí Almanac" acted as a sort of "leap moon" to reset the seasonal calendar back into step with the full moon cycle. The blue moon, as we use it today, resulted from an interpretative error based upon an earlier July 1943 "S&T" article which referenced the 1937 "Maine Farmersí Almanac." The birthing month for the blue moon was March 1946 (in "S&T"). Incidentally, the moon is full on Friday, but it surely isnít blue.
April Star Map