Chandrayaan : Introduction
2008
“MOON”, our closest celestial neighbour, has aroused curiosity much more than any other object in the sky. Moon has been worshipped as deity in different mythologies, called as Chandra / Soma in Indian, Luna in Roman, Selene in Greek and Chang’e in Chinese civilization. One of the oldest Indian scriptures ‘Àgveda’ which originated in Indus valley civilization states.
O Moon! We should be able to know you through our intellect,
You enlighten us through the right path.
Rugveda Part – I/91/1
(About 2000 years B.C)
The Moon with the early history of the solar system etched on it, challenges mankind from time immemorial to discover its secrets and admire its marvels. Understanding the Moon provides a pathway to unravel the early evolution of the solar system and that of planet Earth.
The Moon
The Moon is the brightest object in the night sky, fifth largest satellite of the solar system and only second in brightness to that of the Sun. The Moon orbits the earth at a distance of about 384,400 km, has a diameter of 3,476 km and a mass of 7.35×1022 kg with a mean density of only 13.35 gcm-3 as compared to 5.52 gcm-3 of that of the Earth. It has no atmosphere and outgassing from the surface is negligible. The gravitational force on the Moon is only one sixth of that of the Earth, and not capable of retaining an atmosphere. The absence of any atmosphere causes the Moon to undergo extremes in temperature. The side of the Moon receiving sunlight becomes scorching hot reaching 130 °C. the night side of the Moon reaches freezing cold temperature of -180 °C. The Moon does not have a substantial core of molten iron like Earth and hence, has no intrinsic magnetic field; but it has weak, scattered, localized magnetic anomalies.
An interesting fact is that the Moon always has the same side facing the Earth. This is because Earth’s gravity has slowed the Moon’s rotation in such a way that the rotation time just matches the time it takes to go around the Earth. The Moon’s rotation period around its axis and revolution period around the Earth are same and is about 27? days. Therefore the Moon’s day is equal to its year. The time taken from one new Moon to another new Moon (synodic period) is about 29½ days.
Releted Stories
Tags: Chandrayaan, India, ISRO