Moon Craters and Myths
The beautiful new moon has enthralled people for centuries. Even in ancient times people noticed that its surface did not appear smooth.
There are a number of interesting stories about images on the lunar surface. In the Hindu mythology, the Moon is known by the name Sasanka, which means, with the image of a hare. According to the myth, once there lived a hare, a monkey, a fox and a coot. These friends made a promise that they will not kill any other animals. On seeing this, the God Sakkria decided to test them. He took the shape of a Brahmin and approached each of them for food. As the hare didn’t have anything to offer, he offered himself and the God was so surprised by this gesture that he took the hare with him and painted its image on the Moon so that hare’s goodness will be remembered as long as the world exists.
Lunar Craters: How Are They Formed?
Cosmic bodies like asteroids, comets and meteors, which move freely in outer space, collide with the Moon, leaving behind evidence of their collisions. The moon is a victim of more frequent collisions, as it lacks an atmosphere, which would protect it from the smaller cosmic bodies. Besides that, volcanic eruptions have created craters on its surface. Even our planet Earth has impact craters on its surface. But unlike the Moon, where weather is absent, erosion, precipitation and tectonic activity cause these terrestrial impact craters to erode, and hence become difficult to detect.
Many of the caters on the lunar surface are named after eminent scientists: Copernicus, Archimedes, Moltke, Schrodinger and Tycho are a few of the craters on the Moon so named. The image above shows lunar crater Peary, taken by NASA’s Lunar Reconnaissance Orbiter.
Objects of varying size and speeds collide with the Moon and cause craters of different sizes. As a fast moving object plunges into the lunar surface it compresses the surface creating a depression. Also, the compressed area is accelerated by this impact, while at the same time the compressed lunar surface opposes this action and this resistance decelerates the cosmic impactor. This compression, and subsequent resistance creates a shock wave which propagates through different layers of the lunar surface and the impactor. Due to this shock wave the compressed material is thrown out of the depression formed. The material ejected falls far away from the point of impact. The pressure wave created by this impact is so large that it creates a crater much bigger than the size of the impacting object. The rims of the craters will undergo changes under gravitational impact, where materials on the rim fall into the craters, thus covering part of it. The crater rays, which are formed by the materials ejected during the collision, gives an indication of the age of crater formed. Crater rays appear as bright lines starting from the center of crater. For younger craters the crater rays are more prominent and hence more visible.
List of Craters on the Moon
There are different types of craters.
Simple craters: There are numerous simple craters on lunar surface. These are small in size and hence difficult to detect.
Complex craters: Craters larger than simple craters, and have large basins which are visible from Earth, are grouped as complex craters.
Secondary craters: These are formed by the materials ejected from the impact site.
Halo craters: Those craters in which the rim is covered with materials lighter or darker than the surrounding area are called halo craters.
Weird craters: Those craters which don’t come under any of these classes are grouped as weird craters.
Tycho crater is featured in a number of scientific fiction stories. It is a relatively young crater and is one of the most conspicuous craters on the lunar surface. It spans over 85 km and 4.8 km deep. Its age is estimated to be 108 million years. Scientists believe that it was caused by asteroid from the main asteroid belt, and another asteroid from the same group might have produced the Chicxulub Crater on Earth, which is believed to have wiped out the dinosaurs . The image above shows Tycho Crater.