Stars are always fascinating to mankind. They are the most beautiful celestial bodies, about which mankind contemplates. All the bodies in the universe, including the earth, constitute the celestial bodies. The moon is the celestial body closest to us. Phases of the moon are the most fascinating thing for people of all ages in spite of knowing the science behind the formation of the phases. The moon is a natural satellite of the earth, and it reflects the sunlight incident on it. Due to its revolution around the earth, when it is at different positions in its path, the apparent disc of the moon changes, which gives rise to its phases. When the moon is positioned between the sun and the earth, the illuminated portion of the moon is away from the earth, and we are not able to see the moon. We call this day as the ‘new moon day’. With time, the position of the moon changes and the illuminated portion of the moon exposed to the earth gradually increases. Thus, the size of the apparent disc of the moon increases gradually from a crescent to a full round when the earth lies between the moon and the sun. We call this day the ‘full moon day’.
The duration from one new moon day to the succeeding new moon day is the lunar month. If the moon is observed closely, we find craters, depressions on the surface of the moon, which might have been formed by the collision of some heavenly body like a meteorite with the moon. Even before astronauts landed on the moon, we were able to find information about the universe by celestial objects like meteorites. Meteors are dust-like material, which vary from a small pebble to a big boulder of several hundred kilometre in size, from outer space that enters the earth’s atmosphere. Due to friction between the meteor and the atmosphere, the meteor may get burnt while reaching the surface of the earth. If the size of the meteor is large, a lump of it may be left without getting destroyed in the course of reaching the earth. This part of the meteor is called a meteorite.
The huge distances between the earth and other celestial bodies are measured in light years. A light year is the distance covered by light in one year.