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Astronomy & Astrophysics
Michael Reid

Tides o The Moon is tidally locked to Earth, meaning that the same face of the Moon always faces Earth. o How did the Moon wind up in a tidally locked or synchronous orbit? o Synchronous orbits are caused by tidal gravity o Tidal gravity simply refers to the differencein the force of gravity exerted across some extended body o Tidal gravity comes into play when you start accounting for the real sizes of gravitating bodies. o Tidal gravity causes ocean tides on Earth, the tidal locking of the Moon, volcanoes on Io, destruction of asteroids and comets, etc. o How does gravity cause tides? o Moons gravity pulls harder on near side of Earth than on far side. o Difference in Moons gravitational pull stretches Earth. o The Sun has an effect, too! About half that of the Moon. o Spring tide occurs when the Sun and the Moon (full moon) are aligned. Neap tide occurs when Sun and Moon (last quarter) are perpendicular. o Tidal friction gradually slows Earth rotation (and makes Moon get farther from Earth). o Moon once orbited faster (or slower); tidal friction caused it to lock in synchronous rotation. Friction between the oceans and the Earths crust drags the ocean bulge away from the Earth-Moon line as Earth rotates. Moons gravity pulls back on the bulge, slowing Earths rotation. The Moon steals angular momentum from the spinning Earth and moves farther away. In fact, it moves about 4 centimetres further away from Earth each year, while Earths spin slows down about 2 milliseconds per 100 years. Precession o Precession is the conical shifting of the axis of a rotating object, also known as wobbling. o The Earth is not a perfect sphere; its equatorial diameter is about 26 miles greater than its polar diameter. Earths spinning on its axis causes it to flatten slightly at the poles. o The Earth is not a perfect sphere. At the equator, centrifugal force reduces gravity a little, and therefore the Earth is bigger at the Equator than at the Pole. (This decreases your weight some more at the Equator...). o Oblatenessis a measure of the flatness of a planet, calculated by dividing the difference between the largest and smallest diameter by the largest diameter. o The Earth precessesvery slowly, requiring a period of about 26,000 years. o As the Earth precesses, stars different from Polaris (or no visible stars) occupy the position near the Earths north celestial pole. A corresponding effect is that the position of the vernal equinox changes over the centuries. www.notesolution.com
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