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Solar Eclipse Solar Eclipse Photo of 1999 total eclipse As seen from the Earth, a solar eclipse occurs when the Moon passes between the Sun and the Earth, and the Moon fully or partially covers the Sun as viewed from a location on Earth. This can happen only during a new moon, when the Sun and Moon are in conjunction as seen from Earth. At least two, and up to five, solar eclipses occur each year; no more than two can be total eclipses.[1][2] Total solar eclipses are nevertheless rare at any particular location because totality exists only along a narrow path on the Earth's surface traced by the Moon's umbra. Some people, sometimes referred to as "eclipse chasers" or "umbraphiles",[3][4] will travel to remote locations to observe or witness a predicted central solar eclipse (see Types below). The solar eclipse of August 11, 1999, in Europe helped to increase public awareness of the phenomenon,[citation needed] which apparently led to an unusually large number of journeys made specifically to witness the annular solar eclipse of October 3, 2005, and of March 29, 2006. The last total solar eclipse was the solar eclipse of July 11, 2010; the next will be the solar eclipse of November 13, 2012. The recent solar eclipse of June 1, 2011 and the Solar eclipse of July 1, 2011, were partial eclipses (see Types below); the next partial eclipse will occur on November 25, 2011. A total solar eclipse is a natural phenomenon. Nevertheless, in ancient times, and in some cultures today, solar eclipses have been attributed to supernaturalcauses or regarded as bad omens. A total solar eclipse can be frightening to people who are unaware of their astronomical explanation, as the Sun seems to disappear during the day and the sky darkens in a matter of minutes. Types Annular solar eclipse on October 3, 2005 There are four types of solar eclipses: A total eclipse occurs when the dark silhouette of the Moon completely obscures the intensely bright light of the Sun, allowing the much fainter solarcorona to be visible. During any one eclipse, totality occurs at best only in a narrow track on the surface of the Earth. An annular eclipse occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than that of the Sun. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon. A hybrid eclipse (also called annular/total eclipse) shifts between a total and annular eclipse. At some points on the surface of the Earth it appears as a total eclipse, whereas at others it appears as annular. Hybrid eclipses are comparatively rare. A partial eclipse occurs when the Sun and Moon are not exactly in line and the Moon only partially obscures the Sun. This phenomenon can usually be seen from a large part of the Earth outside of the track of an annular or total eclipse. However, some eclipses can only be seen as a partial eclipse, because the umbra passes above the Earth's polar regions and never intersects the Earth's surface. The Sun's distance from the Earth is about 400 times the Moon's distance, and the Sun's diameter is about 400 times the Moon's diameter. Because these ratios are approximately the same, the Sun and the Moon as seen from Earth appear to be approximately the same size: about 0.5 degree of arc in angular measure. The Moon transiting the Sun as seen fromSTEREO-B on February 25, 2007 at 4.4 times the distance between the Earth and the Moon.[5] The Moon's orbit around the Earth is an ellipse, as is the Earth's orbit around the Sun; the apparent sizes of the Sun and Moon therefore vary.[6][7] Themagnitude of an eclipse is the ratio of the apparent size of the Moon to the apparent size of the Sun during an eclipse. An eclipse that occurs when the Moon is near its closest distance to the Earth (i.e., near its perigee) can be a total eclipse because the Moon will appear to be large enough to cover completely the Sun's bright disk, or photosphere; a total eclipse has a magnitude greater than 1. Conversely, an eclipse that occurs when the Moon is near its farthest distance from the Earth (i.e., near its apogee) can only be an annular eclipse because the Moon will appear to be slightly smaller than the Sun; the magnitude of an annular eclipse is less than 1. Slightly more solar eclipses are annular than total because, on average, the Moon lies too far from Earth to cover the Sun completely. A hybrid eclipse occurs when the magnitude of an eclipse changes during the event from smaller than one to larger than one—or vice versa—so the eclipse appears to be total at some locations on Earth and annular at other locations.[8] Because the Earth's orbit around the Sun is also elliptical, the Earth's distance from the Sun similarly varies throughout the year. This affects the apparent sizes of the Sun and Moon in the same way, but not so much as the Moon's varying distance from the Earth. When the Earth approaches its farthest distance from the Sun in July, a total eclipse is somewhat more likely, whereas conditions favour an annular eclipse when the Earth approaches its closest distance to the Sun in January. Terminology for central eclipse Central eclipse is often used as a generic term for a total, annular, or hybrid eclipse.[9] This is, however, not completely correct: the definition of a central eclipse is an eclipse during which the central line of the umbra touches the Earth's surface. It is possible, though extremely rare, that part of the umbra intersects with Earth (thus creating an annular or total eclipse), but not its central line. This is then called a non-central total or annular eclipse.[10] The next non-central solar eclipse will be on April 29, 2014. This will be an annular eclipse. The next non- central total solar eclipse will be on April 9, 2043.[11] The phases observed during a total eclipse are called: First Contact—when the moon's shadow first becomes visible on the solar disk. Some also name individual phases between First and Second Contact e.g. Pac-Man phase. Second Contact—starting with Baily's Beads {caused by light shining through valleys on the moon's surface} and the Diamond Ring. Almost the entire disk is covered. Totality—with the shadow of the moon obscuring the entire disk of the sun and only the corona visible Third Contact—when the first bright light becomes visible and the shadow is moving away from the sun. Again a Diamond Ring may be observed Predictions Geometry A Total eclipse in the umbra. B Annular eclipse in the antumbra. C Partial eclipse in the penumbra The diagram to the right shows the alignment of the Sun, Moon and Earth during a solar eclipse. The dark gray region below the Moon is theumbra, where the Sun is completely obscured by the Moon. The small area where the umbra touches the Earth's surface is where a total eclipse can be seen. The larger light gray area is the penumbra, in which only a partial and annular eclipses can be seen. The Moon's orbit around the Earth is inclined at an angle of just over 5 degrees to the plane of the Earth's orbit around the Sun (the ecliptic). Because of this, at the time of a new moon, the Moon will usually pass above or below the Sun. A solar eclipse can occur only when the new moon occurs close to one of the points (known as nodes) where the Moon's orbit crosses the ecliptic. As noted above, the Moon's orbit is also elliptical. The Moon's distance from the Earth can vary by about 6% from its average value. Therefore, the Moon's apparent size varies with its distance from the Earth, and it is this effect that leads to the difference between total and annular eclipses. The distance of the Earth from the Sun also varies during the year, but this is a smaller effect. On average, the Moon appears to be slightly smaller than the Sun, so the majority (about 60%) of central eclipses are annular. It is only when the Moon is closer to the Earth than average (near its perigee) that a total eclipse occurs.[12][13] Moon Sun At At perigee At apogee At aphelion perihelion (nearest) (farthest) (farthest) (nearest) Mean 1,737.10 kilometres 696,000 kilometres radius, r (1,079.38 miles) (432,000 miles) 147,098,070 152,097,700 363,104 km 405,696 km km km Distance, d (225,622 mi) (252,088 mi) (91,402,500 (94,509,100 mi) mi) Angular diameter, 32' 54" 29' 26" 32' 32" 31' 28" 2 × (0.5482°) (0.4907°) (0.5422°) (0.5244°) arctan(r / d) Apparent size to scale Rank in descending 1st 4th 2nd 3rd order The Moon orbits the Earth in approximately 27.3 days, relative to a fixed frame of reference. This is known as the sidereal month. However, during one sidereal month, the Earth has revolved part way around the Sun, making the average time between one new moon and the next longer than the sidereal month: it is approximately 29.5 days. This is known as the synodic month, and corresponds to what is commonly called the lunar month.
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