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eclipse

(ēklĭps`, ĭ–) [Gr.,=failing], in astronomy, partial or total obscuring of one celestial body by the shadow of another. Best known are the lunar eclipses, which occur when the earth blocks the sun's light from the moon, and solar eclipses, occurring when the moon blocks the sun's light from a small portion of the earth. Occasionally a double or binary star system is aligned so that one star eclipses the other as seen from the earth; these stars are known as eclipsing binaries. Also important to science have been the eclipses of Jupiter's satellites; in 1675 the Danish astronomer Ole Roemer used these eclipses to calculate the speed of light. Observations of starlight passing near the sun during the 1919 solar eclipse were of particular value in validating Einstein's general theory of relativity.

Lunar Eclipses

Since the earth and moon shine only by the reflected light of the sun, each casts a shadow into space in the direction away from the sun. The shadow consists of a cone-shaped area of darkness called the umbra, where all light from the sun is cut off, and a larger area of partial darkness called the penumbra, which surrounds the umbra and receives light from a part of the sun's disk. Lunar eclipses can occur only when the moon is in its full phase, i.e., when the earth is between the sun and the moon. These eclipses may be total or partial, depending on whether the moon passes completely into the umbra of the earth's shadow or remains partly in the penumbra. Since the moon cuts the umbra close to the base, it can experience long periods of total eclipse ranging up to 1 hr, 42 min. A partial eclipse (when it passes through the penumbra) can last more than 2 hr, and the entire lunar eclipse may continue for as long as 4 hr. Some light is refracted, or bent, by the earth's atmosphere into the umbra, so that the moon at totality, instead of appearing black, ranges from a dull gray to a coppery color, depending on the amount of dust in the earth's atmosphere.

Solar Eclipses

A total solar eclipse can occur only when the moon is in its new phase. At this time the moon is between the sun and the earth and cannot be seen until it moves across the sun's disk. At the onset of totality, parts of the sun may be seen shining brightly between the high points of the moon's irregular edge, a phenomenon known as Baily's beads; the disk of the moon appears black and is surrounded by the sun's coronacorona,
luminous envelope surrounding the sun, outside the chromosphere. Its density is less than one billionth that of the earth's atmosphere. The corona is visible only at the time of totality during a total eclipse of the sun.
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, out of which shoot immense, flamelike spurts called prominences. The sky darkens to twilight, the brightest stars become visible, and there is a noticeable drop in temperature. Baily's beads are seen again as the sun reappears and the sky grows lighter.

At apogee (when the moon is at its farthest point from the earth) the umbra of its shadow is too short to reach the earth's surface, causing the apparent diameter of the sun's disk to be larger than that of the moon. Where the moon would otherwise block the sun entirely, now the sun is seen as a bright ring completely surrounding the moon's disk; this eclipse is known as an annular, or ring, eclipse. The longest possible duration of totality for a solar eclipse is 7 min, 40 sec at or near the equator when the sun is directly overhead; the duration decreases with increasing latitude. The eclipse of June 20, 1955, lasted 7 min, 8 sec, which was the longest duration of totality in 1,238 years; an eclipse almost as long occurred on July 11, 1991.

Frequency and Prediction of Eclipses

If the plane of the moon's orbit about the earth coincided with that of the earth about the sun, a solar eclipse would be observed each month when the moon is new and a lunar eclipse when the moon is full. However, the moon's orbital plane is tilted at an angle of about 5°10' to the earth's orbital plane, making eclipses possible only when the three bodies are aligned (at new or full moon) and when the moon is crossing the earth's orbital plane (at a point called the nodenode,
in astronomy, point at which the orbit of a body crosses a reference plane. One reference plane that is often used is the plane of the earth's orbit around the sun (ecliptic).
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). Within a given year, a maximum of seven eclipses can occur, either four solar and three lunar or five solar and two lunar. Despite the fact that there are more solar than lunar eclipses each year, over time many more lunar eclipses are seen at any single location on earth than solar eclipses. This occurs because a lunar eclipse can be seen from the entire half of the earth facing the moon at that time, while a solar eclipse is visible only along a narrow path on the earth's surface.

From their observations of eclipses the Chaldaeans (fl. 1000 B.C.–540 B.C.) discovered that similar eclipses of the sun recur in cycles of 18 years, 11 1-3 days; this cycle, called the saros, is an interval in which the sun, earth, and moon return to nearly identical relative positions. Since the orbits of the earth and moon are quite accurately known, eclipses can be predicted far in advance, both in time and location. Similar calculations can determine the time and place of past eclipses; this information is useful for dating historical events that are known to have occurred at the same time as an eclipse.

Eclipseclick for a larger image
Eclipse: (a) solar and lunar eclipses; (b) lunar shadow in solar eclipse

eclipse

The total or partial obscuration of light from a celestial body as it passes through the shadow of another body. A planetary satellite is eclipsed when it passes through the shadow of its primary or another satellite. An eclipse of the Sun is strictly an occultation.

An eclipse of the Sun – a solar eclipse – or the Moon – a lunar eclipse – occurs when the Sun, Moon, and Earth lie in or nearly in a straight line: see illustration (a). If the plane of the Moon's orbit lay exactly in the plane of the ecliptic a solar eclipse would take place at each new Moon and a lunar eclipse at each full Moon. The two planes are however inclined at an angle of about 5°, intersecting at the nodes of the Moon's orbit. Eclipses are only observed when the Sun is at or near a node and the Moon is near the same node (solar eclipse) or the opposite one (lunar eclipse). The ecliptic limits are the maximum angular distances of the new or full Moon from its node for an eclipse to take place.

Although the Moon is 400 times smaller than the Sun, it is also about 400 times nearer the Earth. As a result, Sun and Moon have almost exactly the same angular size (about ½°), so that it is possible for the Moon to obscure the Sun. The Earth and Moon both cast shadows in sunlight, the shadow having a dark cone-shaped inner region – the umbra – and an outer lighter penumbral region. A solar eclipse occurs, between sunrise and sunset at new Moon, when the Moon passes directly in front of the Sun so that the Earth lies in the Moon's shadow: see illustration (b). When the Moon is sufficiently close to Earth so that its apparent diameter exceeds that of the Sun, then the umbra of the Moon's shadow can just reach the Earth's surface. It moves in a general west to east trend over a very narrow curved zone of the surface, known as the path of totality, which can be up to 250 km wide but averages about 160 km. An observer at a point where only the penumbra will move past sees a partial eclipse, in which only part of the Sun is obscured. An observer in the path of totality will experience a total eclipse, in which the Sun is completely obscured. If the Moon is far enough away to appear smaller than the Sun, a rim (or annulus) of light will be seen around the eclipsed Sun and an annular eclipse occurs. The period of annularity never exceeds 12.5 minutes and is normally much less.

In a total solar eclipse, first contact occurs when the Moon just appears to touch the Sun's western limb. As the Moon gradually covers the Sun, the landscape darkens and animals become disturbed. Totality begins at second contact when the Sun disappears from sight. The maximum duration of totality is 7m 31s but is usually much less. Totality ends at third contact, just as the crescent Sun emerges, and at fourth contact the whole disk of the Sun is once more seen. The time between first and last contact can approach four hours. During totality the chromosphere, corona, and other phenomena can be observed and studied. There are between two and five solar eclipses each year. Total eclipses are, however, very rare at any particular place.

A lunar eclipse occurs, at full Moon, when the Moon passes into the shadow cone of the Earth. It can be seen from any place at which the Moon is visible above the horizon. A total eclipse occurs when the Moon enters completely into the umbra of the Earth's shadow. If only part of the Moon enters the umbra the eclipse is partial. When the Moon only enters the penumbral region, a penumbral eclipse takes place in which a slight, usually quite unappreciable darkening of the Moon's surface occurs. The maximum duration of totality is 1h 47m. The Moon can usually be seen throughout totality, being illuminated by sunlight refracted by the Earth's atmosphere into the shadow area. Since the bluer wavelengths are removed by scattering, the Moon has a coppery-red color. There are up to either two or three lunar eclipses each year. Up to seven eclipses can occur in one year, either five solar and two lunar or four solar and three lunar.

See also saros.

Eclipse

(religion, spiritualism, and occult)

An eclipse is the full or partial obscuring of the Sun by the Moon (a solar eclipse), or the full or partial obscuring of the Moon by the Sun (a lunar eclipse). When planets and stars are obscured by another celestial body (particularly by the Moon), it is called an occultation. The orbits of the Sun and Moon intersect, but are not parallel; if they were parallel, a solar eclipse would occur during every new moon and a lunar eclipse every full moon. Eclipses can occur only when the Sun and Moon intersect the lunar nodes.

Traditionally, the influence of eclipses, whether full or partial, has been regarded as negative, portending famine, war, and the like. Also, with respect to individual natal charts, the traditional interpretation is that an eclipse exerts a malefic influence, particularly if it falls on or near (within 5° of) a natal planet or an angle. Contemporary astrologers tend to see eclipses as indicating emphasis or a crisis in the affairs related to the house in which the eclipse occurs. For instance, should an eclipse occur in a person’s second house, she or he may be compelled to attend to financial matters. Should the eclipse occur near (within 5° of) a natal planet or be directly opposed to (180° away from, give or take 5°) a natal planet, the crisis will be a major one and will be colored by the nature of the planet or planets involved.

Sources:

Brau, Jean-Louis, Helen Weaver, and Allan Edmands. Larousse Encyclopedia of Astrology. New York: New American Library, 1980.
Jansky, Robert Carl. Interpreting the Eclipses. San Diego: Astro Computing, 1979.
Michelsen, Neil F. Tables of Planetary Phenomena. San Diego: Astro Computing, 1979.

What does it mean when you dream about an eclipse?

The sun is often taken to represent the conscious, rational self and the moon, the subconscious, emotional self. Their union in an eclipse may signify a coming together of separate parts of oneself (self-integration). It may also stand for the “eclipsing” of reason or consciousness by emotion or the subconscious (in a solar eclipse), or vice versa (in a lunar eclipse). We sometimes speak of being “eclipsed,” and this may also be the meaning of a dream about eclipses.

eclipse

[i′klips]
(astronomy)
The reduction in visibility or disappearance of a body by passing into the shadow cast by another body.
The apparent cutting off, wholly or partially, of the light from a luminous body by a dark body coming between it and the observer. Also known as astronomical eclipse.

eclipse

regarded as portent of misfortune. [World Folklore: Leach, 337]

eclipse

1. the total or partial obscuring of one celestial body by another. A solar eclipse occurs when the moon passes between the sun and the earth; a lunar eclipse when the earth passes between the sun and the moon
2. the period of time during which such a phenomenon occurs

ECLIPSE

A Prolog + CLP compiler from ECRC.

Eclipse

(1) An open source Java-based platform for integrating software tools for application development. Running under Windows and Linux, it provides a universal platform for tools created as Eclipse plug-ins. IBM started the Eclipse consortium in late 2001 with USD $40 million and donated a large amount of code. In 2004, it was spun off as an independent foundation. For more information, visit www.eclipse.org. See NetBeans.

(2) (ECLIPSE) An early series of 32-bit minicomputers from Data General. The development of the initial 32-bit ECLIPSE MV/8000 was the subject of Tracy Kidder's best-selling book, "Soul of a New Machine" published in 1981 by Little, Brown and Company.