Syzygie

_Syzygy In astronomy, a syzygy (ˈsɪzədʒi ; ) is a roughly straight-line configuration of three or more celestial bodies in a gravitational system. When Earth is one of the bodies involved, the other objects appear to be close together (or overlapping) in the sky. The word is often used in reference to the Sun, Earth, and either the Moon or a planet, where the latter is in conjunction or opposition. Solar and lunar eclipses occur at times of syzygy, as do transits and occultations. The term is often applied when the Sun and Moon are in conjunction (new moon) or opposition (full moon). A syzygy sometimes results in an occultation, transit, or an eclipse. An occultation occurs when an apparently larger body passes in front of an apparently smaller one. A transit occurs when a smaller body passes in front of a larger one. In the combined case where the smaller body regularly transits the larger, an occultation is also termed a secondary eclipse. An eclipse occurs when a body totally or partially disappears from view, either by an occultation, as with a solar eclipse, or by passing into the shadow of another body, as with a lunar eclipse (thus both are listed on NASA's eclipse page). Einstein ring As electromagnetic rays are affected by gravitation, when they pass by a heavy mass they are bent. As a result the heavy mass acts as a form of gravitational lens. If the light source, the gravitating mass and the observer stand in a line, one sees what is termed an Einstein ring. A syzygy causes the fortnightly phenomena of spring and neap tides. At the new and full moon, the Sun and Moon are in syzygy. Their tidal forces act to reinforce each other, and the ocean both rises higher and falls lower than the average. Conversely, at the first and third quarter, the Sun and Moon are at right angles, their tidal forces counteract each other, and the tidal range is smaller than average. Tidal variations can also be measured in the Earth's crust, and these Earth tide influences may affect the frequency of earthquakes.