Imagine how frightened prehistoric people must have been when they saw a black disk covering up the sun. This darkening of the sun In the middle of the day is called eclipse. The moon can go dark in a similar way at night.
An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer
The term eclipse is most often used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond the Earth-Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A binary star system can also produce eclipses if the plane of the orbit of its constituent stars intersects the observer's position.
An eclipse cycle takes place when a series of eclipses are separated by a certain interval of time. This happens when the orbital motions of the bodies form repeating harmonic patterns. A particular instance is the saros, which results in a repetition of a solar or lunar eclipse every 6,585.3 days, or a little over 18 years (because this is not a whole number of days, successive eclipses will be visible from different parts of the world)
In fact, there are two kinds of eclipse: the eclipse of the sun and the eclipse of the moon.
The progression of a solar eclipse on August 1, 2008, viewed from Novosibirsk, Russia. The time between shots is three minutes.As observed from the Earth, a solar eclipse occurs when the Moon passes in front of the Sun. The type of solar eclipse event depends on the distance of the Moon from the Earth during the event. A total solar eclipse occurs when the Earth intersects the umbra portion of the Moon's shadow. When the umbra does not reach the surface of the Earth, the Sun is only partially occulted, resulting in an annular eclipse. Partial solar eclipses occur when the viewer is inside the penumbra.
The eclipse magnitude is the fraction of the Sun's diameter that is covered by the Moon. For a total eclipse, this value is always greater than or equal to one. In both annular and total eclipses, the eclipse magnitude is the ratio of the angular sizes of the Moon to the Sun.
Geometry of a total solar eclipse (not to scale)When observed at points in space other than from the Earth's surface, the Sun can be eclipsed by bodies other than the Moon. Two examples are when the crew of Apollo 12 observed the Earth to eclipse the Sun in 1969 and when the Cassini probe observed Saturn to eclipse the Sun in 2006.
Main article: Lunar eclipse
lunar eclipse. Totality is shown with the last two images to lower right. These required a longer exposure time to make the details visible.Lunar eclipses occur when the Moon passes through the Earth's shadow. Since this occurs only when the Moon is on the far side of the Earth from the Sun, lunar eclipses only occur when there is a full moon. Unlike a solar eclipse, an eclipse of the Moon can be observed from nearly an entire hemisphere. For this reason it is much more common to observe a lunar eclipse from a given location. A lunar eclipse also lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour.
There are three types of lunar eclipses: penumbral, when the Moon crosses only the Earth's penumbra; partial, when the Moon crosses partially into the Earth's umbra; and total, when the Moon crosses entirely into the Earth's umbra. Total lunar eclipses pass through all three phases. Even during a total lunar eclipse, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere enters the umbra and provides a faint illumination. Much as in a sunset, the atmosphere tends to more strongly scatter light with shorter wavelengths, so the illumination of the Moon by refracted light has a red hue, thus the phrase 'Blood Moon' is often found in descriptions of such lunar events as far back as eclipses are recorded
Sumber : wikipedia.com