Star Points for May, 1998; by Curtis Roelle Eye on the Moon Tonight (Sunday, May 3) a beautiful half-full 1st quarter moon will be hanging in the southern sky after sunset. From our distant vantage point on earth the moon appears round but its true shape is that of a ball. At any given time exactly one-half of the spherical moon is illuminated by the sun's light. (There is an exception however: during a total lunar eclipse.) So why do the moon's "phases" change from night to night? Orbiting earth at an average distance of nearly one quarter million miles, the moon completes its cycle of phases in 29.5 days. This period is called the "synodic" month. The moon is called "new" when it is on the same side of the earth as the sun. At this time we cannot see the moon because the side facing us is not illuminated by sunlight. The new moon rises and sets with the sun. New moon was one week ago on April 26. When the moon has gone 1/4 of the way around the sun the right side appears half full to people in earth's northern half. (In the southern hemisphere the moon is "upside down" so the illuminated half is on the left.) The "first quarter" moon rises around noon and sets approximately at midnight. Having completed half of its orbit around the earth the moon is "full". This month full moon is on May 11. The moon rises at sunset and sets near sunrise. When the moon has completed 3/4 of its orbit it again appears half full, but now the left half is illuminated. The "third quarter" moon occurs on May 19, rising near midnight and setting around noon. The new moon returns on May 25. When is the best time to look at the moon with a telescope or binoculars? Tonight or any night within a day or two of 1st quarter. There are several reasons for this. 1. The moon is up as soon as it gets dark. You don't need to set the alarm and get up in the middle of the night to see it. 2. The "terminator" crosses the center of the moon and is hence seen straight on. The terminator is the line that separates day and night on the moon. Along this line objects such as craters, mountains, and valleys are much more visible because they have shadows that are long and dramatic. 3. Even the unlit portion of the moon can appear dimly illuminated by "earth shine". Earth shine is light reflected from earth's oceans which illuminates the darkened lunar landscape. Earth shine seen from the U.S. during the evening is caused by sunlight reflected off the Pacific Ocean. Earth shine in the morning before sunrise is caused by light scattering off the Atlantic Ocean. The moon is an object which never disappoints no matter how small a telescope is used to view it. Passing a pair of binoculars between family members or friends can be a memorable experience leading to a lifelong passion of star gazing. For web surfers there are several good guides for learning more about and observing the moon. "The Hitchhiker's Guide to the Moon" and "The Lunar Website" are two of the best around.