In astronomy, a syzygy is a roughly straight-line configuration of three or more celestial bodies in a gravitational system. as viewed by the Curiosity rover on Mars.
Overview
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 or opposition. The word syzygy is often used to describe interesting configurations of astronomical objects in general. For example, one such case occurred on March 21, 1894, around 23:00 GMT, when Mercury transited the Sun as would have been seen from Venus, and Mercury and Venus both simultaneously transited the Sun as seen from Saturn. It is also used to describe situations when all the planets are on the same side of the Sun although they are not necessarily in a straight line, such as on March 10, 1982. On June 3, 2014, the Curiosity rover on Mars observed the planet Mercury transiting the Sun, marking the first time a planetary transit has been observed from a celestial body besides Earth.
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.
Transits and occultations of the Sun by Earth's Moon are called solar eclipses regardless of whether the Sun is completely or partially covered. By extension, transits of the Sun by a satellite of a planet may also be called eclipses, as with the transits of Phobos and Deimos shown on , as may the passage of a satellite into the planet's shadow, as with this . The term eclipse is also used more generally for bodies passing in front of one another. For example, refers to the Moon eclipsing and occulting Saturn interchangeably.
Einstein ring
As electromagnetic rays are somewhat bent by gravitation, when they pass by a heavy mass they are bent. Thus, the heavy mass acts as a form of gravitational lens. If the light source, the diffracting mass and the observer stand ina line, one sees what is termed an Einstein ring.
