This is a brief look at the issues of Lunar light and shadow.
First, consider that the limit of either light or shadow is the horizon, which is much closer on the Moon than on Earth. On flat terrain such as a Mare, consider the horizon as less than two kilometers distance. A 500 meter peak may cast a shadow over forty kilometers distant – far “over the horizon.”
Effectively this is why the lunar North and South pole could not be imaged until LRO did it with radar. Consider the solar terminator moving the line of sunlight and dark across the lunar surface. The Moon has a slight axial tilt relative to the Sun, so the point we call the “North Pole” is not 90 degrees tangent to the Sun.
Because of the lack of an atmosphere, the transition from light to dark is sudden, abrupt and total. Continue reading Light and shadow on the Moon
