Endless sky aliens3/20/2023 ![]() The blinding glare tends to discourage observation of the low-contrast surface markings visible here. Still farther into the daylit hemisphere, the ground blazes under the high Sun like a desert at noon. A few bits of shadow can be found quite far into the Moon's day region, cast by the steepest hills and crater walls. Here shadows are shorter and fewer, and the ground is much more brightly lit. The left image shows Copernicus just after local sunrise the right image shows it with the Sun nearly overhead.Īway from the terminator, the Sun stands higher in the lunar sky. ![]() Sometimes changes can be detected in just a few minutes an hour is enough to modify everything along the sunrise or sunset line.Īs the Sun climbs higher in the lunar sky, a once-familiar crater can take on an unusual appearance. As the terminator creeps from the Moon's east to west (which is west to east in an earthbound telescope's field of view), the shadows gradually alter and new features come into daylight or vanish into night. But the features are certainly real, if amplified, and offer endless scope for exploring. The extreme contrast makes an overly strong impression on eyes that are used to Earth's softer lighting. Since the Moon has no atmosphere, the shadows are almost night black against the daylit land. The exaggeration of relief is due to the long, sharp shadows cast by every small irregularity when the Sun is low on the lunar horizon. The craggy mountains are usually just rolling hills, the black canyons shallow vales. In reality the Moon is not nearly as rugged as it looks near the terminator. Farther into the bright disk, the land seems much smoother. Here the landscape is a tangle of bold detail - crags, canyons, and seemingly bottomless craters filled with black shadow ringed by brilliant sunlit walls. Most lunar observing is done near the terminator, for reasons that become clear with the first look through a telescope. In the waning phases, the two weeks after full, the terminator is the line of sunset. At full Moon it coincides with the edge of the disk (the limb) and is not seen. As the Moon grows ( waxes) during the two weeks after new, the terminator is the line of sunrise, unveiling new terrain as it slowly sweeps across the lunar surface. The first thing evident about this landscape is that it's divided by the terminator, the line separating lunar day and night. Click on the image to see the surround terrain including the craters Ptolemaeus, Alphonsus, and nearby Arzachel. The dark line on the floor of Mare Nubium is the Straight Wall, discernible here only by the shadow it casts at sunrise. So it's fair to say there are really two types of observing: the Moon and everything else. Being so close, the Moon presents a landscape, not a skyscape. Its mean distance is hardly astronomical 239,000 miles (382,400 kilometers) may be less than you've driven a car during its lifetime. The lunar surface shows thousands of times more detail than anything else in the night sky, being over 100 times closer than the nearest planet ever gets. So if a 3-inch telescope gives an equally good view of such a world close by, why not take advantage of it? If a 10,000-mile-aperture telescope giving sharp images at a billion power could be turned to the nearest stars, many planets coming into view would most likely resemble the Moon. But of course the Moon is the same body it always was.Įven deep-space enthusiasts should consider it important to their subject, rather than just a bright nuisance, because it surely represents a standard type of world throughout the universe: an airless, geologically dead rockball covered with the impact craters of its formation and youth. It's as if Luna suddenly ceased to be an astronomical object once we walked on it. Since the Apollo landings there has been a definite loss of interest in the Moon. "Well," she demanded, "why don't they tell anyone?"Īmateur astronomers tend to be much more jaded. "How long have they known about this?" she asked. One evening I showed the first-quarter Moon in my 6-inch reflector to a visiting real-estate agent. The Moon is one celestial object that lives up to expectations the first time it's seen in a telescope, and it never fails to impress even casual viewers. ![]() This is usually the lunar face that beginning observers first study as every month it's nicely placed in the sunset sky. A crescent Moon is a visually pleasing combination of dark maria and bright, rugged lunar highlands.
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