One theory suggested that a nomadic, Indo European tribe, called the Aryans, invaded and conquered the Indus Valley Civilization. The eastward shift of monsoons may have reduced the water supply, forcing the Harappans of the Indus River Valley to migrate and establish smaller villages and isolated farms.
Astrolabe
is a very ancient astronomical computer for solving problems relating to time and the position of the Sun and stars in the sky. Several types of astrolabes have been made. By far the most popular type is the planispheric astrolabe, on which the celestial sphere is projected onto the plane of the equator