Medium Telescope Lunar Observing Challenge
In addition to viewing lunar craters in detail, a 3- to 4-inch refracting telescope, or a 6- to 8-inch reflecting telescope, brings lunar geology into view. The mountain chains forming the rim of the impact basins cradling some of the circular maria come into sharp view. Craters that have been modified by volcanism after their violent origin by meteor impact can be distinguished. A modest telescope will reveal rilles, or channels carved into the lunar surface by volcanic and tectonic forces. Shallow and delicate wrinkle ridges formed by compression of layers of basalt on the lunar seas are also seen in detail. The wispy streaks of crater rays can be traced.
The Moon is admittedly a world that has shown no significant physical change during the 400 year history of telescopic study, but our neighboring world is far from static. A modest telescope will show the ongoing dynamic daily changes on the Moon by following the hour by hour progression of sunrise shadows as they recede from mountain and craters. The appearance of geologic features on the face of the Moon also changes as the sun progressively illuminates the cycle of phases. As shadows disappear under noontime sun, some major craters seem to vanish from view while others become highly reflective with their floors or crater rims taking on searchlight brilliance. No two views of the Moon are the same, there are always new delights for the telescopic observer.