Bob Moler's Ephemeris Blog

This is Bob Moler with Ephemeris for Monday, April 24th. Today the Sun will be up for 13 hours and 55 minutes, setting at 8:38, and it will rise tomorrow at 6:42. The Moon, 3 days before first quarter, will set at 2:02 tomorrow morning.

The Moon’s changing appearance over the month may seem to be mysterious at first glance. Maybe because one may think that the objects in the sky are somehow different from the familiar objects we see around us on the Earth. In ancient times, especially the Greeks, thought that everything in the heavens was perfect and spotless. They explained the definite markings we see as the man-in-the-moon as a reflection of the Earth by a spotless Moon. The Moon’s phases are simply light and shadow on a ball in the sunlight. Sometime, when the Moon appears in the daytime, take a small ball, like a golf ball and hold it up to the Moon, while the ball is also in sunlight, and the small ball will exhibit the same phase as the Moon.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EST, UT –4 hours). They may be different for your location.

Addendum

This is the best diagram of the Moon’s phases and how the it appears from the Earth. Credit http://planetfacts.org/phases-of-the-moon/ which I recommend.

A demonstration of the Moon’s crescent phase with the styrofoam moon ball we use for Project Astro held up to a light off frame to the right. The line between the bright (day) and dark (night) side of the ball, moon or planet is called the terminator. The night side of the ball is illuminated a bit by the translucency of the ball, and the reflection off my hand. Note the roughness of the ball is visible only at the terminator, where the shadows are longest. I photographed this outside at night to minimize the ball’s nighttime illumination.