<Tr> <Td> </Td> <Td> This section needs additional citations for verification . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (December 2016) (Learn how and when to remove this template message) </Td> </Tr> <P> There are preserved observations of solar and lunar eclipses from Babylonian astronomy and Chinese astronomy beginning from the 8th century BCE . These observations, as well as further astronomical historical records from astronomy in the medieval Islamic world and elsewhere, can be used to determine the actual changes in the rotation of the Earth over the last 27 centuries: The calculation to describe the place and time of eclipse is dependent on the rotation of the Earth . The ancient observations are consistent with the Earth having rotated a significant fraction of a total turn than would result from today's value of the speed of rotation would indicate: The Earth was turning ever faster throughout the past . The cumulative effect of the faster turn, of a magnitude of milliseconds per day per century, 36,525 days per century, shows up in a magnitude of hours and thousands of kilometers in observations . Scholars have combed the ancient records and calculated by modern models the magnitude of the long term historical slowing down of the Earth's rotation . </P> <P> The Earth's original rotation was a vestige of the original angular momentum of the cloud of dust, rocks, and gas that coalesced to form the Solar System . This primordial cloud was composed of hydrogen and helium produced in the Big Bang, as well as heavier elements ejected by supernovas . As this interstellar dust is heterogeneous, any asymmetry during gravitational accretion resulted in the angular momentum of the eventual planet . </P> <P> However, if the giant - impact hypothesis for the origin of the Moon is correct, this primordial rotation rate would have been reset by the Theia impact 4.5 billion years ago . Regardless of the speed and tilt of the Earth's rotation before the impact, it would have experienced a day some five hours long after the impact . Tidal effects would then have slowed this rate to its modern value . </P>

Earth spins on its rotation axis in a counterclockwise direction