StarWatch for the greater Lehigh Valley

APRIL  2009


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

[Moon Phases]
Solar X-rays:  
Geomagnetic Field:  
Status Current Moon Phase
659    APRIL 5, 2009:   Dating Easter
Sunday, April 12, as all of us know is Easter. Last year at this time, Easter had already taken place, March 23rd. During some years Easter happens in late March, as early as the 22nd (last 1818 and next 2285). Easter may occur as late as April 25 (last 1943 and next 2038). If the occurrence of Easter is defined as the first Sunday after the first full moon after the vernal (spring) equinox, then there is a 92.2 percent chance that the date will be correct. The rules decreed by the Catholic Church were that Easter was to fall on the first Sunday after the 14th day of the lunar month that fell on or after March 21. The 14th day of the lunar month is not equivalent to the day of full moon which occurs on average about 14.77 days into the lunar phase cycle of 29.53 days. Another way of describing this is to say that Easter falls on the first Sunday after the Paschal (Passover) full moon, the 14th day of the moon. The Paschal full moon must occur on or after March 21, but it is derived strictly through a mathematical calculation which can deviate as much as two days from the actual time of the full moon. If the date of Easter were not unified, then Christís resurrection could occur on multiple dates. As an example, let us say that the moon was full at 11 p.m. in California on a Saturday on or after March 21. For people on Pacific Daylight Time, Easter would occur on the following day. For us, three time zones to the east and three hours later, the moon would be full at 2 a.m. Sunday. According to the general rule, Easter for the East Coast could not occur until the following Sunday. Take the year 2009 and divide it by 19 (105.74). Multiply the .74 by 19 to get 14. The number 14 always corresponds to the Paschal full moon date of April 10 (Friday, this year). Easter must therefore occur on Sunday, April 12, everywhere.

[Dates of Easter Through 2014]

660    APRIL 12, 2009:   Galileoscope: Bargain of the Century
The year 2009 marks the International Year of Astronomy in celebration of the 400th anniversary of Galileoís first telescopic observations of the heavens made during the late summer and fall of 1609. Galileo Galilei, as many people incorrectly believe, did not invent the telescope. The Dutch optician, Hans Lippershey, is generally given credit for that. His patent application had to supply a working instrument. Galileo was also not the first person to turn a telescope towards the heavens, but he was the first to publish his results in a small book entitled Sidereus Nuncius (Starry Messenger). Here he described his observations of our cratered moon, sunspots and the rotation of the sun, the phases of Venus, and the four large moons of Jupiter. In addition, Galileo noticed an oddity associated with Saturn, which one day would be discovered to be its rings, and the proliferation of stars in the hazy ribbon of light that straddles the nighttime sky that today we call our Milky Way galaxy. In honor of Galileoís achievements, the International Astronomical Union, the world congress of astronomers and chief sponsor of IYA 2009, has developed a quality telescope for the mass market which will be made available to the public in late April. The refractor has a two-inch diameter lens. A second lens corrects for color, a problem in most inexpensive refractors, and it is designed for interchangeable, inch-and-a-quarter diameter eyepieces, a standard in the industry. The price for the 30 piece kit which takes five minutes to assemble, according to IYA 2009 officials, is $15 plus shipping. Even if youíre spatially impaired and it takes an hour, it still might be the greatest bargain of the century. More information can be garnered at

The Galileoscope may be one of the best telescope bargains of the century. It is designed to show the heavens as Galileo first saw them in 1609, but with an optical quality that Galileo could never have imagined or achieved. Images supplied from

661    APRIL 19, 2009:   Lyrids: First Major Meteor Event
The week of April 19 marks the beginning of the meteor season with the Lyrid shower putting on the first major act since early January. Comet Thatcher, an interloper that requires 415 years to travel around the sun, is responsible for the Lyrid display. During the winter months and early spring, the Earth simply does not intersect any large amount of organized cometary debris. It is the dust from a cometís tail coming close to Earthís orbital path which triggers an increase in the rate of shooting star activity, as well as the radiant, the undisputed indicator that these meteor events are related to each other. The larger sandy particles released by the nucleus in the cometís outgassing process generally follow the cometís orbit. The meteoroid particles are moving parallel to each other, so when they enter Earthís atmosphere, they appear to diverge from their common position of origin in similar fashion to a long stretch of roadway which diverges from a vanishing point far into the distance. In astronomy this is called the radiant, and the Lyrids radiate from a part of the summer sky in the constellation of the Lyra the Harp just to the right (south) of the brilliant, blue-white star Vega. Lyra and Vega are almost mid-sky in the ENE by 1 a.m. on the morning of the 22nd when the Lyrids are predicted to be most active. But donít expect the sky to be ablaze with shooting stars. Rates are normally about 5-10 events per hour. Meteor trails will point back towards Vega. The optimal time for observing Lyrid activity should be about an hour before dawn, 3:45-4:45 a.m. when Vega will be that really bright star near the zenith. All youíll have to do is lay out on a tarp inside the cozy comfort of a sleeping bag with a soft pillow under your head and gaze straight up. Just donít let the stillness and serenity of the morning sky and fragrance of the pungent spring air put you to sleep. Good observing!

662    APRIL 26, 2009:   Twinkle Slowly Little Mercury
Readers of this column know that Mercury is my favorite planet to view and photograph. I certainly enjoy observing the others, but the sheer difficulty of spotting Mercury because of its proximity to the sun gives it the edge. To see Mercury clearly means having an observing location with a flat, unobscured western or eastern horizon and a transparent enough atmosphere so that Mercury can be distinguished as a starlike object against the brighten dawn or dimming twilight sky. Binoculars are particularly handy for determining whether you have snagged a planet or you are simply looking at a bright star. Stars twinkle (scintillate); planets do not. That rule needs modification when making observations nearer to the horizon where the long corridor of air that the light is passing through causes everything to scintillate. Here, the twinkling effect will be less pronounced for planets than for the stars. This week presents an especially good opportunity for viewing the Messenger God. Using binoculars, view near to the WNW horizon about 45 minutes after sundown. Sunday, April 26 is the primo evening because a very thin slivery moon will lie only four degrees above Mercury. The bow of the crescent will point towards the horizon and Mercury. Look for the ďold moon in the new moonís arms,Ē as twilight deepens. It is the ghostly appearance of the unlit portion of the moonís surface reflecting the light from a nearly full Earth back to us again. Mercury will be visible in the WNW all week, while the moonís crescent, in its journey around the Earth, thickens and reaches first quarter by Friday, May 1. Donít get confused by the brighter winter stars of the constellations of Taurus, Orion, and Canis Major. They will all be to Mercuryís left and nearing the horizon at the same time. Enjoy!

[Moon, Mercury and the Pleiades]
The moon, the Pleiades star cluster, and Mercury light up the twilight sky on April 26. If the clouds near the horizon look more like summer, that was because the temperature in Coopersburg, PA had reached into the low 90s earlier in the day, unprecedented warmth for mid-spring. An equatorially mounted Canon 40D camera was used to image this 10 sec., 112mm, F/4.5 exposure of the western horizon. The scene was equally impressive through binoculars. Photography by Gary A. Becker...

[Moon and Mercury]

[April Star Map]

[April Moon Phase Calendar]