On Thursday night, April 22, the sun will rise over the oneof the most spectacular topographic features on the moon ? the Straight Wall ?giving skywatchers a good chance to spot the lunar marvel.
The moon is the only astronomical body on whichtopographical features can be seen in detail with small telescopes or evenbinoculars. It is fascinating to watch the sunlight playing on these featuresas themoon rotates.
To locate the Straight Wall (or Rupes Recta, as it?sformally known in Latin) first look for the trio of large craters right in thecenter of the terminator, the line dividing light and shadow on the moon?ssurface: Ptolemaeus, Alphonsus, and Arzachel. Just to the southwest of Arzachelis a large ruined crater, flooded by lava from the Mare Nubium. The StraightWall is a huge fault crossing this ghost crater. [See the moon's Straight Wall.]
At this time in the lunar month, the Straight Wall, 68miles (110 km) long, casts a wide shadow. Despite this, it is really not veryhigh, ranging from 800 to 1,000 feet (240?300 meters) in height. Heights ofobjects close to the terminator are often exaggerated by the glancing rays ofthe sun.
Although the slope of this fault line looks steep, it isreally quite gentle compared to similar fault lines on Earth, only about sevendegrees. A cluster of hills at the southern end of the Straight Wall oftenlooks like the handle of a sword, the blade being formed by the Straight Wallitself. Just to the west of the Straight all is the small but deep crater Birt,which is 11 miles (17 km) in diameter and 11,400 feet (3,470 meters) deep.
It will be interesting to look at this area again in alittle under two weeks, on the morning of May 6, when the sun is setting on theStraight Wall. The face of the wall, currently in shadow, will then be bathedin the light of the settingsun, a brilliant white line instead of the current black one.
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This article was provided to SPACE.com by Starry Night Education, theleader in space science curriculum solutions.
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