Solar eclipse

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Geometry of a Total Solar Eclipse (not to scale).

Photo of 1999 total eclipse.

A solar eclipse occurs when the moon passes between the Sun and the Earth so that the Sun is fully or partially covered. This can only happen during a new moon, when the Sun and Moon are in conjunction as seen from the Earth. At least two and up to five solar eclipses can occur each year on Earth, with between zero and two of them being total eclipses.^[1][2] Total solar eclipses are nevertheless rare at any location because during each eclipse totality exists only along a narrow corridor in the relatively tiny area of the Moon's umbra.

A total solar eclipse is a spectacular natural phenomenon and many people travel to remote locations to observe one. The solar eclipse of August 11, 1999 in Europe helped to increase public awareness of the phenomenon, as illustrated by the number of journeys made specifically to witness the total solar eclipse of October 3, 2005 and the total solar eclipse of March 29, 2006. The recent solar eclipse of January 26, 2009, was an annular eclipse (see below), while the solar eclipse of July 22, 2009 was a total solar eclipse.

In ancient times, and in some cultures today, solar eclipses have been attributed to supernatural causes. Total solar eclipses can be frightening for people who are unaware of their astronomical explanation, as the Sun seems to disappear in the middle of the day and the sky darkens in a matter of minutes.

[edit] Types

Annular solar eclipse on October 3, 2005

There are four types of solar eclipses:

• A total eclipse occurs when the Sun is completely obscured by the Moon. The intensely bright disk of the Sun is replaced by the dark silhouette of the Moon, and the much fainter corona is visible. During any one eclipse, totality is visible only from at most 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) transitions between a total and annular eclipse. At some points on the surface of the Earth it is visible as a total eclipse, whereas at others it is 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 never intersects the Earth's surface, passing above the Earth's polar regions.

The Sun's distance from the Earth is about 390 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 in front of the Sun as seen from STEREO-B on February 25, 2007 at 4.4 times the distance between the Earth and the Moon.^[3]

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.^[4][5] The magnitude 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 when the Moon is near its closest distance from 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 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 transitions 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.^[6]

The Earth's orbit around the Sun is also elliptical, so the Earth's distance from the Sun varies throughout the year. This also affects the apparent sizes of the Sun and Moon, but not so much as the Moon's varying distance from the Earth. When the Earth approaches its farthest distance from the Sun (the aphelion) in July, this tends to favor a total eclipse. As the Earth approaches its closest distance from the Sun (the perihelion) in January, this tends to favor an annular eclipse.

[edit] Terminology

Central eclipse is often used as a generic term for a total, annular, or hybrid eclipse. 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.^[7] 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.^[8]

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 {cause 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

[edit] Predictions

[edit] Geometry

Diagram of solar eclipse (not to scale).

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 the umbra, 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 eclipse 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.^[9][10]

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.

A Total eclipse in the umbra.
B Annular eclipse in the antumbra.
C Partial eclipse in the penumbra

The Moon crosses from south to north of the ecliptic at its ascending node, and vice versa at its descending node. However, the nodes of the Moon's orbit are gradually moving in a retrograde motion, due to the action of the Sun's gravity on the Moon's motion, and they make a complete circuit every 18.6 years. This means that the time between each passage of the Moon through the ascending node is slightly shorter than the sidereal month. This period is called the draconic month.

Finally, the Moon's perigee is moving forwards in its orbit, and makes a complete circuit in about 9 years. The time between one perigee and the next is known as the anomalistic month.

The Moon's orbit intersects with the ecliptic at the two nodes that are 180 degrees apart. Therefore, the new moon occurs close to the nodes at two periods of the year approximately six months apart, and there will always be at least one solar eclipse during these periods. Sometimes the new moon occurs close enough to a node during two consecutive months. This means that in any given year, there will always be at least two solar eclipses, and there can be as many as five. However, some are visible only as partial eclipses, because the umbra passes above Earth's north or south pole, and others are central only in remote regions of the Arctic or Antarctic.^[11][12]

[edit] Path

During a central eclipse, the Moon's umbra (or antumbra, in the case of an annular eclipse) moves rapidly from west to east across the Earth. The Earth is also rotating from west to east, but the umbra always moves faster than any given point on the Earth's surface, so it almost always appears to move in a roughly west-east direction across a map of the Earth (there are some rare exceptions to this which can occur during an eclipse of the midnight sun in Arctic or Antarctic regions).

The width of the track of a central eclipse varies according to the relative apparent diameters of the Sun and Moon. In the most favourable circumstances, when a total eclipse occurs very close to perigee, the track can be over 250 km wide and the duration of totality may be over 7 minutes. Outside of the central track, a partial eclipse can usually be seen over a much larger area of the Earth.^[13]

[edit] Occurrence and cycles

Total Solar Eclipse Paths: 1001–2000. This image was merged from 50 separate images from NASA.^[14]

Total solar eclipses are rare events. Although they occur somewhere on Earth every 18 months on average,^[15] it has been estimated that they recur at any given place only once every 370 years, on average. The total eclipse only lasts for a few minutes at that location, as the Moon's umbra moves eastward at over 1700 km/h. Totality can never last more than 7 min 31 s, and is usually much shorter: during each millennium there are typically fewer than 10 total solar eclipses exceeding 7 minutes. The last time this happened was June 30, 1973 (7 min 3 sec). Observers aboard a Concorde aircraft were able to stretch totality to about 74 minutes by flying along the path of the Moon's umbra. The next eclipse exceeding seven minutes in duration will not occur until June 25, 2150. The longest total solar eclipse during the 8,000-year period from 3000 BCE to 5000 AD will occur on July 16, 2186, when totality will last 7 min 29 s.^[16] For comparison, the longest eclipse of the 21st century occurred on July 22, 2009 and lasted 6 min 39 sec.

If the date and time of any solar eclipse are known, it is possible to predict other eclipses using eclipse cycles. Two such cycles are the Saros and the Inex. The Saros cycle is probably the best known, and one of the most accurate, eclipse cycles. The Inex cycle is itself a poor cycle, but it is very convenient in the classification of eclipse cycles. After a Saros cycle finishes, a new Saros cycle begins one Inex later, hence its name: in-ex. A Saros cycle lasts 6,585.3 days (a little over 18 years), which means that after this period a practically identical eclipse will occur. The most notable difference will be a shift of 120° in longitude (due to the 0.3 days) and a little in latitude. A Saros series always starts with a partial eclipse near one of Earth's polar regions, then shifts over the globe through a series of annular or total eclipses, and ends at the opposite polar region. A Saros (series) lasts 1226 to 1550 years and 69 to 87 eclipses, with about 40 to 60 central.^[17]

[edit] Frequency per year

Solar eclipses can occur 2 to 5 times per calendar year. Since the Gregorian calendar was begun in 1582, five solar eclipses occurred in 1693, 1758, 1823, 1805, 1870, 1935. The next occurrence will be 2206.^[18]

For example the 5 solar eclipses of 1935 were:

January 5	February 3		June 30	July 30		December 25
Partial (south)	Partial (north)		Partial (north)	Partial (south)		Annular (north)
Saros 111	Saros 149		Saros 116	Saros 154		Saros 121

[edit] Final totality

Spectacular solar eclipses are an extreme rarity within the universe at large. They are seen on Earth because of a fortuitous combination of circumstances. Even on Earth, spectacular eclipses of the type familiar to people today are a temporary (on a geological time scale) phenomenon. Many millions of years in the past, the Moon was too close to the Earth to precisely occult the Sun as it does during eclipses today; and many millions of years in the future, it will be too far away to do so.

Due to tidal acceleration, the orbit of the Moon around the Earth becomes approximately 3.8 cm more distant each year. It is estimated that in 600 million years, the distance from the Earth to the Moon will have increased by 23,500 km, meaning that it will no longer be able to completely cover the Sun's disk. This will be true even when the Moon is at perigee, and the Earth at aphelion.^[19]

A complicating factor is that the Sun will increase in size over this timescale. This makes it even more unlikely that the Moon will be able to cause a total eclipse. Therefore the last total solar eclipse on Earth will occur in slightly less than 600 million years.

[edit] Historical eclipses

Astronomers Studying an Eclipse by Antoine Caron

Historical eclipses are a valuable resource for historians, in that they allow a few historical events to be precisely dated, from which other dates and a society's calendar can be deduced. Aryabhata (476–550) concluded the Heliocentric theory in solar eclipse. A solar eclipse of June 15, 763 BCE mentioned in an Assyrian text is important for the Chronology of the Ancient Orient. Also known as the eclipse of Bur Sagale, it is the earliest solar eclipse mentioned in historical sources that has been successfully identified. Perhaps the earliest still-unproven claim is that of archaeologist Bruce Masse; on the basis of several ancient flood myths that mention a total solar eclipse, he links an eclipse that occurred May 10, 2807 BCE with a possible meteor impact in the Indian Ocean.^[20] There have been other claims to date earlier eclipses, notably that of Mursili II (likely 1312 BCE), in Babylonia, and also in China, during the 5th year (2084 BCE) of the regime of Emperor Zhong Kang of Xia dynasty, but these are highly disputed and rely on much supposition.^[21][22]

Herodotus wrote that Thales of Miletus predicted an eclipse which occurred during a war between the Medians and the Lydians. Soldiers on both sides put down their weapons and declared peace as a result of the eclipse. Exactly which eclipse was involved has remained uncertain, although the issue has been studied by hundreds of ancient and modern authorities. One likely candidate took place on May 28, 585 BCE, probably near the Halys river in the middle of modern Turkey.^[23]

An annular eclipse of the Sun occurred at Sardis on February 17, 478 BCE, while Xerxes was departing for his expedition against Greece, as Herodotus recorded.^[24] Hind and Chambers considered this absolute date more than a century ago.^[25] Herodotus also reports that another solar eclipse was observed in Sparta during the next year, on August 1, 477 BCE.^[26][27][28] The sky suddenly darkened in the middle of the day, well after the battles of Thermopylae and Salamis, after the departure of Mardonius to Thessaly at the beginning of the spring of (477 BCE) and his second attack on Athens, after the return of Cleombrotus to Sparta. The modern conventional dates are different by a year or two, and that these two eclipse records have been ignored so far.^[29] The Chronicle of Ireland recorded a solar eclipse on June 29, 512 CE, and a solar eclipse was reported to have taken place during the Battle of Stiklestad in July, 1030.

It has also been attempted to establish the exact date of Good Friday by means of solar eclipses, but this research has not yielded conclusive results.^[30] Research has manifested the inability of total solar eclipses to serve as explanations for the recorded Good Friday features of the crucifixion eclipse.^[31] (Good Friday is recorded as being at Passover, which is also recorded as being at or near the time of a full moon.)

The ancient Chinese astronomer Shi Shen (fl. 4th century BCE) was aware of the relation of the moon in a solar eclipse, as he provided instructions in his writing to predict them by using the relative positions of the moon and sun.^[32] The 'radiating influence' theory for a solar eclipse (i.e., the moon's light was merely light reflected from the sun) was existent in Chinese thought from about the 6th century BCE (in the Zhi Ran of Zhi Ni Zi),^[33] and opposed by the Chinese philosopher Wang Chong (27–97 CE), who made clear in his writing that this theory was nothing new.^[34] This can be said of Jing Fang's writing in the 1st century BCE, which stated:

The moon and the planets are Yin; they have shape but no light. This they receive only when the sun illuminates them. The former masters regarded the sun as round like a crossbow bullet, and they thought the moon had the nature of a mirror. Some of them recognized the moon as a ball too. Those parts of the moon which the sun illuminates look bright, those parts which it does not, remain dark.^[33]

The ancient Greeks had known this as well, since it was Parmenides of Elea around 475 BCE who supported the theory of the moon shining because of reflected light, and was accepted in the time of Aristotle as well.^[33] The Chinese astronomer and inventor Zhang Heng (78–139 CE) wrote of both solar and lunar eclipses in the publication of Ling Xian in 120 CE, supporting the radiating influence theory that Wang Chong had opposed (Wade-Giles):

The sun is like fire and the moon like water. The fire gives out light and the water reflects it. Thus the moon's brightness is produced from the radiance of the sun, and the moon's darkness (pho) is due to (the light of) the sun being obstructed (pi). The side which faces the sun is fully lit, and the side which is away from it is dark. The planets (as well as the moon) have the nature of water and reflect light. The light pouring forth from the sun (tang jih chih chhung kuang) does not always reach the moon owing to the obstruction (pi) of the earth itself—this is called 'an-hsü', a lunar eclipse. When (a similar effect) happens with a planet (we call it) an occulation (hsing wei); when the moon passes across (kuo)(the sun's path) then there is a solar eclipse (shih).^[35]

The later Chinese scientist and statesman Shen Kuo (1031–1095 CE) also wrote of eclipses, and his reasoning for why the celestial bodies were round and spherical instead of flat (Wade-Giles spelling):

The Director [of the Astronomical Observatory] asked me about the shapes of the sun and moon; whether they were like balls or (flat) fans. If they were like balls they would surely obstruct (ai) each other when they met. I replied that these celestial bodies were certainly like balls. How do we know this? By the waxing and waning (ying khuei) of the moon. The moon itself gives forth no light, but is like a ball of silver; the light is the light of the sun (reflected). When the brightness is first seen, the sun(-light passes almost) alongside, so the side only is illuminated and looks like a crescent. When the sun gradually gets further away, the light shines slanting, and the moon is full, round like a bullet. If half of a sphere is covered with (white) powder and looked at from the side, the covered part will look like a crescent; if looked at from the front, it will appear round. Thus we know that the celestial bodies are spherical...Since the sun and moon are in conjunction (ho) and in opposition (tui) once a day, why then do they have eclipses only occasionally?' I answered that the ecliptic and the moon's path are like two rings, lying one over the other (hsiang tieh), but distant by a small amount. (If this obliquity did not exist), the sun would be eclipsed whenever the two bodies were in conjunction, and the moon would be eclipsed whenever they were exactly in position. But (in fact) though they may occupy the same degree, the two paths are not (always) near (each other), and so naturally the bodies do not (intrude) upon one another.^[36]

Eclipses have been interpreted as omens, or portents, especially when associated with battles. On 22 January 1879 a British battalion was massacred by Zulu warriors during the Zulu War in South Africa. At 2:29 PM there was a solar eclipse.^[37] The conflict was named the Battle of Isandlwana, the Zulu name for the battle translates as "the day of the dead moon".^[38]

[edit] Viewing

The Pinhole Projection Method of observing partial Solar Eclipse. At the insert in the upper left corner of this image you can see the partially eclipsed sun that was photographed with a white solar filter. At the bottom of the image you can see the projection of the partially eclipsed sun.

Looking directly at the photosphere of the Sun (the bright disk of the Sun itself), even for just a few seconds, can cause permanent damage to the retina of the eye, because of the intense visible and invisible radiation that the photosphere emits. This damage can result in permanent impairment of vision, up to and including blindness. The retina has no sensitivity to pain, and the effects of retinal damage may not appear for hours, so there is no warning that injury is occurring.^[39]

Under normal conditions, the Sun is so bright that it is difficult to stare at it directly, so there is no tendency to look at it in a way that might damage the eye. However, during an eclipse, with so much of the Sun covered, it is easier and more tempting to stare at it. Unfortunately, looking at the Sun during an eclipse is just as dangerous as looking at it outside an eclipse, except during the brief period of totality, when the Sun's disk is completely covered (totality occurs only during a total eclipse and only very briefly; it does not occur during a partial or annular eclipse). Viewing the Sun's disk through any kind of optical aid (binoculars, a telescope, or even an optical camera viewfinder) is extremely hazardous.^[40]

Glancing at the Sun with all or most of its disk visible is unlikely to result in permanent harm, as the pupil will close down and reduce the brightness of the whole scene. If the eclipse is near total, the low average amount of light causes the pupil to open. Unfortunately the remaining parts of the Sun are still just as bright, so they are now brighter on the retina than when looking at a full Sun. As the eye has a small fovea, for detailed viewing, the tendency will be to track the image on to this best part of the retina, causing damage.

[edit] Partial and annular eclipses

Eclipse glasses.

Viewing the Sun during partial and annular eclipses (and during total eclipses outside the brief period of totality) requires special eye protection, or indirect viewing methods, if eye damage is to be avoided. The Sun's disk can be viewed using appropriate filtration to block the harmful part of the Sun's radiation. Sunglasses do not make viewing the sun safe. Only properly designed and certified solar filters should ever be used for direct viewing of the Sun's disk.^[41] Especially, self-made filters using common objects like a floppy disk removed from its case, a Compact Disc, a black colour slide film, etc. must be avoided despite what may have been said in the media.^[42]

The safest way to view the Sun's disk is by indirect projection. This can be done by projecting an image of the disk onto a white piece of paper or card using a pair of binoculars (with one of the lenses covered), a telescope, or another piece of cardboard with a small hole in it (about 1 mm diameter), often called a pinhole camera. The projected image of the Sun can then be safely viewed; this technique can be used to observe sunspots, as well as eclipses. However, care must be taken to ensure that no one looks through the projector (telescope, pinhole, etc.) directly. Viewing the Sun's disk on a video display screen (provided by a video camera or digital camera) is safe, although the camera itself may be damaged by direct exposure to the Sun. The optical viewfinders provided with some video and digital cameras are not safe. Securely mounting #14 welder's glass in front of the lens and viewfinder protects the equipment and makes viewing possible. Professional workmanship is essential because of the dire consequences any gaps or detaching mountings will have. In the partial eclipse path one will not be able to see the spectacular corona or nearly complete darkening of the sky, yet, depending on how much of the sun's disk is obscured, some darkening may be noticeable. If two-thirds or more of the sun is obscured, then an effect can be observed by which the daylight appears to be dim, as if the sky were overcast, yet objects still cast sharp shadows.

[edit] Totality

It is safe to observe the total phase of a solar eclipse directly with the unaided eye, binoculars or a telescope, when the Sun's photosphere is completely covered by the Moon. During this period the sun is too dim to be seen through filters. The Sun's faint corona will be visible, and the chromosphere, solar prominences, and possibly even a solar flare may be seen. However, viewing the Sun after totality can be dangerous.

Baily's beads.

When the shrinking visible part of the photosphere becomes very small, Baily's beads will occur. These are caused by the sunlight still being able to reach Earth through lunar valleys, but no longer where mountains are present. Totality then begins with the diamond ring effect, the last bright flash of sunlight.^[43]

At the end of totality, the same effects will occur in reverse order, and on the opposite side of the moon.

[edit] Photography

Photographing an eclipse is possible with fairly common camera equipment. In order for the disk of the sun/moon to be easily visible, a fairly high magnification telephoto lens is needed (70–200 mm for a 35 mm camera), and for the disk to fill most of the frame, a longer lens is needed (over 500 mm). As with viewing the sun directly, looking at it through the viewfinder of a camera can produce damage to the retina, so care is advised.^[44]

[edit] Other observations

The progression of a solar eclipse on August 1, 2008 in Novosibirsk, Russia. All times UTC (local time was UTC+7). The time span between shots is 3 minutes.

For astronomers, a total solar eclipse forms a rare opportunity to observe the corona (the outer layer of the Sun's atmosphere). Normally this is not visible because the photosphere is much brighter than the corona. According to the point reached in the solar cycle, the corona can appear small and symmetric, or large and fuzzy. It is very hard to predict this prior to totality.^[45]

During a solar eclipse, special (indirect) observations can also be done with the unaided eye only. Normally the spots of light which fall through the small openings between the leaves of a tree, have a circular shape. These are images of the Sun. During a partial eclipse, the light spots will show the partial shape of the Sun, as seen on the picture. Another famous phenomenon is shadow bands (also known as flying shadows), which are similar to shadows on the bottom of a swimming pool. They only occur just prior to and after totality, and are very difficult to observe. Many professional eclipse chasers have never seen them.^[46]

During a partial eclipse, a related effect that can be seen is anisotropy in the shadows of objects. Particularly if the partial eclipse is nearly total, the unobscured part of the sun acts as an approximate line source of light. This means that objects cast shadows which have a very narrow penumbra in one direction, but a broad penumbra in the perpendicular direction.

[edit] 1919 observations

The original photograph of the 1919 eclipse which was claimed to confirm Einstein's theory of general relativity.

The observation of a total solar eclipse of May 29, 1919 helped to confirm Einstein's theory of general relativity. By comparing the apparent distance between two stars, with and without the Sun between them, Arthur Eddington stated that the theoretical predictions about gravitational lenses were confirmed, though it now appears the data were ambiguous at the time. The observation with the Sun between the stars was only possible during totality, since the stars are then visible.^[47]

[edit] Gravity anomalies

There is a long history about the observations of gravity-related phenomena during solar eclipses, especially around totality. In 1954 and again in 1959, Maurice Allais reported that his observations of the strange/unexplained movement during solar eclipses^[48] This phenomenon is now called the Allais Effect. Similarly, Saxl and Allen in 1970 observed another event of the sudden change in motion of a torsion pendulum, and this phenomenon is called the Saxl effect^[49]

A recent published observation during the 1997 solar eclipse by Wang et al.^[50] suggested a possible gravitational shielding effect, though there is some serious debate. Later in 2002, Yang and Wang published the detailed data analysis suggested that the phenomenon still remain unexplained.^[51] More studies are being planned by NASA and ESA over the next decade.

[edit] Before sunrise, after sunset

The phenomenon of atmospheric refraction makes it possible to observe the Sun (and hence a solar eclipse) even when it is slightly below the horizon. It is however possible for a solar eclipse to attain totality (or in the event of a partial eclipse, near-totality) before (visual and actual) sunrise or after sunset from a particular location. When this occurs shortly before the former or after the latter, the sky will appear much darker than it would otherwise be immediately before sunrise or after sunset. On these occasions, an object (especially a planet, often Mercury) may be visible near the sunrise or sunset point of the horizon when it could not have been seen without the eclipse.^[52]

[edit] Eclipses and transits

In principle, the simultaneous occurrence of a Solar eclipse and a transit of a planet is possible. But these events are extremely rare because of their short durations. The next anticipated simultaneous occurrence of a Solar eclipse and a transit of Mercury will be on July 5, 6757, and a Solar eclipse and a transit of Venus is expected on April 5, 15232.^[53]

Only 5 hours after the transit of Venus on June 4, 1769, there was a total solar eclipse, which was visible in Northern America, Europe and Northern Asia as partial solar eclipse. This was the lowest time difference between a transit of a planet and a solar eclipse in the historical past.

More common, but still infrequent, is a conjunction of any planet (not only Mercury or Venus) at the time of a total solar eclipse, in which event the planet will be visible very near the eclipsed Sun, when without the eclipse it would have been lost in the Sun's glare. At one time, some scientists hypothesized that there may be a planet (often given the name Vulcan) even closer to the Sun than Mercury; the only way to confirm its existence would have been to observe it during a total solar eclipse. It is now known that no such planet exists. While there does remain some possibility for small Vulcanoid asteroids to exist, none have ever been found.

[edit] Artificial satellites

Shadow of the moon above Turkey and Cyprus, seen from the ISS during a 2006 solar eclipse.

Artificial satellites can also pass in front of, or transit, the Sun as seen from Earth, but none are large enough to cause an eclipse. At the altitude of the International Space Station, for example, an object would need to be about 3.35 km across to blot the Sun out entirely. These transits are difficult to watch, because the zone of visibility is very small. The satellite passes over the face of the Sun in about a second, typically. As with a transit of a planet, it will not get dark.^[54]

Artificial satellites do play an important role in documenting solar eclipses. Images of the umbra on the Earth's surface taken from Mir and the International Space Station are among the most spectacular of all eclipse images.^[55] Observations of eclipses from satellites orbiting above the Earth's atmosphere are not subject to weather conditions.

The direct observation of a total solar eclipse from space is rare. The only documented case is Gemini 12 in 1966. The partial phase of the 2006 total eclipse was visible from the International Space Station. At first, it looked as though an orbit correction in the middle of March would bring the ISS in the path of totality, but this correction was postponed.^[56]

[edit] Meteorological measurements

A special weather station used for meteorological measurements during solar eclipses.^[57]

A marked drop of the intensity of the solar radiation occurs during solar eclipse. It influences the actions in the atmosphere. The variations of the atmospheric actions display in changes of standard meteorological and physical quantities. These can be noticed by a measurement of the air temperature and other meteorological quantities (e.g.: air humidity, soil temperature, colour of the solar radiation).

The progressions of the quantities are usually detected by special weather stations because of a short duration of a total (annular) solar eclipse. The properties of the devices usually are: high speed of measurement, high resolution and sensitivity. Acquired results show variations in progressions of meteorological and physical quantities (e.g.: colour of the light).^[57]

[edit] Recent and upcoming solar eclipses

Short term eclipse cycles repeat every 6 lunations (every 177 days), each set lasting 3–4 years. They occur at either the ascending and descending nodes of the moon's orbit. Each set has the moon's shadow crossing the earth near the north or south pole, and subsequent events progress towards the other pole until it misses the earth and the series ends. The saros cycle increments by 5 within each set, and 5 different sets repeat every 18 years, the saros period.

[edit] 1990-1992

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 1990–1992

Ascending node				Descending node
Saros	Map	Photo		Saros	Map	Photo
				121	January 26, 1990 Annular
126	July 22, 1990 Total			131	January 15, 1991 Annular
136	July 11, 1991 Total			141	January 4, 1992 Annular
146	June 30, 1992 Total			151	December 24, 1992 Partial

[edit] 1993-1996

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 1993–1996

Ascending node				Descending node
Saros	Map	Photo		Saros	Map	Photo
118	May 21, 1993 Partial			123	November 13, 1993 Partial
128	May 10, 1994 Annular			133	November 3, 1994 Total
138	April 29, 1995 Annular			143	October 24, 1995 Total	Totality at Dundlod, India
148	April 17, 1996 Partial			153	October 12, 1996 Partial

[edit] 1997-2000

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 1997–2000

Ascending node				Descending node
Saros	Map	Photo		Saros	Map	Photo
120	March 9, 1997 Total			125	September 2, 1997 Partial
130	February 26, 1998 Total			135	August 22, 1998 Annular
140	February 16, 1999 Annular			145	August 11, 1999 Total	Totality France
150	February 5, 2000 Partial			155	July 31, 2000 Partial
Partial solar eclipses on July 1, 2000 and December 25, 2000 occur in the next lunar year eclipse set.

[edit] 2000-2003

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Note: Partial solar eclipses on February 5, 2000 and July 31, 2000 occur in the previous lunar year set.

Solar eclipse series sets from 2000–2003

Ascending node				Descending node
Saros	Map	Photo		Saros	Map	Photo
117	July 1, 2000 Partial (south)			122	December 25, 2000 Partial (north)
127	June 21, 2001 Total	Totality from Zambia		132	December 14, 2001 Annular	Partial from Minneapolis, MN
137	June 10, 2002 Annular	Partial Los Angeles, CA		142	December 4, 2002 Total
147	May 31, 2003 Annular	Partial from Belfort		152	November 23, 2003 Total

[edit] 2004-2007

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 2004–2007

Ascending node				Descending node
Saros	Map	Photo		Saros	Map	Photo
119	2004 April 19 Partial (south)			124	2004 October 14 Partial (north)
129	2005 April 8 Hybrid			134	2005 October 3 Annular	Annular from Spain
139	2006 March 29 Total	Totality from Side, Turkey		144	2006 September 22 Annular	Partial from São Paulo, Brazil
149	2007 March 19 Partial (north)			154	2007 September 11 Partial (south)

[edit] 2008-2011

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 2008–2011

Ascending node				Descending node
Saros	Map	Photo		Saros	Map	Photo
121	2008 February 7 Annular			126	2008 August 1 Total	Total from Russia
131	2009 January 26 Annular			136	2009 July 22 Total	Total from Bangladesh
141	2010 January 15 Annular			146	2010 July 11 Total
151	2011 January 4 Partial (north)			156	2011 July 1 Partial (south)
Partial solar eclipses on June 1, 2011 and November 25, 2011 occur on the next lunar year eclipse set.

[edit] 2011-2014

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Note: Partial solar eclipses on January 4, 2011 and July 1, 2011 occur in the previous lunar year eclipse set.

Solar eclipse series sets from 2011–2014

Ascending node			Descending node
118	June 1, 2011 Partial		123	November 25, 2011 Partial
128	May 20, 2012 Annular		133	November 13, 2012 Total
138	May 10, 2013 Annular		143	November 3, 2013 Hybrid
148	April 29, 2014 Annular		153	October 23, 2014 Partial

[edit] 2015-2018

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 2015–2018

Ascending node			Descending node
120	March 20, 2015 Total		125	September 13, 2015 Partial
130	March 9, 2016 Total		135	September 1, 2016 Annular
140	February 26, 2017 Annular		145	August 21, 2017 Total
150	February 15, 2018 Partial		155	August 11, 2018 Partial
Partial solar eclipses on July 13, 2018 and January 6, 2019 occur on the next lunar year eclipse set.

[edit] 2018-2021

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Note: Partial solar eclipses on February 15, 2018 and August 11, 2018 occur on the previous lunar year eclipse set.

Solar eclipse series sets from 2018–2021

Ascending node			Descending node
117	July 13, 2018 Partial		122	January 6, 2019 Partial
127	July 2, 2019 Total		132	December 26, 2019 Annular
137	June 21, 2020 Annular		142	December 14, 2020 Total
147	June 10, 2021 Annular		152	December 4, 2021 Total

[edit] 2022-2025

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 2022-2025

Ascending node			Descending node
119	April 30, 2022 Partial		124	October 25, 2022 Partial
129	April 20, 2023 Hybrid		134	October 14, 2023 Annular
139	April 8, 2024 Total		144	October 2, 2024 Annular
149	March 29, 2025 Partial		154	September 21, 2025 Partial

‎

[edit] 2026-2029

This set of solar eclipses repeat approximately every 177 days and 4 hours at alternating nodes of the moon's orbit.

Solar eclipse series sets from 2026-2029

Ascending node			Descending node
121	February 17, 2026 Annular		126	August 12, 2026 Total
131	February 6, 2027 Annular		136	August 2, 2027 Total
141	January 26, 2028 Annular		146	July 22, 2028 Total
151	January 14, 2029 Partial		156	July 11, 2029 Partial
Partial solar eclipses on June 12, 2029 and December 5, 2029 occur in the next lunar year eclipse set.

[edit] See also

[edit] Eclipses elsewhere

• Solar eclipses on Jupiter
• Solar eclipses on Pluto
• Transit of Deimos from Mars
• Transit of Phobos from Mars

[edit] Eclipse lists

• Articles on individual solar eclipses
• List of solar eclipses

[edit] Miscellaneous

• Allais effect
• Crucifixion eclipse
• Lunar eclipse
• Solar eclipses in fiction

[edit] Notes

[edit] References

• Needham, Joseph (1986). Science and Civilization in China: Volume 3. Taipei: Caves Books, Ltd.

[edit] External links

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[edit] General

• Solar eclipse of January 15, 2010
• Solar eclipse of January 15, 2010, F. Espenak, NASA
• Animated explanation of the mechanics of a solar eclipse, University of Glamorgan
• Solar eclipse time sequence
• NASA's Eclipse Home Page, Fred Espenak
• Search among the 11,898 solar eclipses over five millennium and display interactive maps
• Detailed eclipse explanations and predictions, Hermit Eclipse
• Prof. Druckmüller's eclipse photography site
• World Atlas of Solar Eclipse Paths, F. Espenak
• Animated maps of past and future solar eclipses.
• Looking Back at an Eclipsed Earth 1999 August 11 from Mir EO-27 - Astronomy Picture of the Day 2007 June 10

[edit] Eye safety

• Eye Safety During Solar Eclipses, F. Espenak (NASA Goddard Space Flight Center)
• How to Watch a Partial Solar Eclipse Safely, A. M. MacRobert (Sky & Telescope magazine)
• UK hospitals assess eye damage after solar eclipse, British Medical Journal, August 21, 1999, p. 319–469

Links to related articles v • d • e Solar eclipses Lists of eclipses Antiquity · 20th century BCE · 19th century BCE · 18th century BCE · 17th century BCE · 16th century BCE · 15th century BCE · 14th century BCE · 13th century BCE · 12th century BCE · 11th century BCE · 10th century BCE · 9th century BCE · 8th century BCE · 7th century BCE · 6th century BCE · 5th century BCE · 4th century BCE · 3rd century BCE · 2nd century BCE · 1st century BCE · 1st century · 2nd century · 3rd century · 4th century · 5th century · 6th century · 7th century · 8th century · 9th century · 10th century · 11th century · 12th century · 13th century · 14th century · 15th century · 16th century · 17th century · 18th century · 19th century · 20th century · 21st century · 22nd century · 23rd century · 24th century · 25th century · 26th century · 27th century · 28th century · 29th century · 30th century Eclipses seen from: China · the United Kingdom · Philippines Saros cycles: 110 · 111 · 112 · 113 · 114 · 115 · 116 · 117 · 118 · 119 · 120 · 121 · 122 · 123 · 124 · 125 · 126 · 127 · 128 · 129 · 130 · 131 · 132 · 133 · 134 · 135 · 136 · 137 · 138 · 139 · 140 · 141 · 142 · 143 · 144 · 145 · 146 · 147 · 148 · 149 · 150 · 151 · 152 · 153 · 154 · 155 · 156 · 157 · 158 · 159 · 160 · 161 · 162 Historical eclipses Mursili's eclipse (1312 BC) · Assyrian eclipse (763 BC) · Battle of Halys (585 BC) · Crucifixion darkness and eclipse Past Total/hybrid eclipses 1715 May 3 · 1778 Jun 24 · 1806 Jun 16 · 1842 Jul 8 · 1851 Jul 28 · 1858 Sep 7 · 1860 Jul 18  · 1868 Aug 18 · 1870 Dec 22 · 1878 Jul 29 · 1882 May 17  · 1883 May 6  · 1885 Sep 8  · 1886 Aug 29  · 1887 Aug 19  · 1889 Dec 22  · 1889 Jan 1 · 1893 Apr 16  · 1896 Aug 9  · 1898 Jan 22  · 1900 May 28 · 1901 May 18 · 1903 Sep 21 · 1904 Sep 9 · 1905 Aug 30 · 1907 Jan 14 · 1908 Jan 3 · 1908 Dec 23 · 1909 Jun 17 · 1910 May 9 · 1911 Apr 28 · 1912 Apr 17 · 1912 Oct 10 · 1914 Aug 21 · 1916 Feb 3 · 1918 Jun 8 · 1919 May 29 · 1921 Oct 1 · 1922 Sep 21 · 1923 Sep 10 · 1925 Jan 24 · 1926 Jan 14 · 1927 Jun 29 · 1928 May 19 · 1929 May 9 · 1930 Apr 28 · 1930 Oct 21 · 1932 Aug 31 · 1934 Feb 14 · 1936 Jun 19 · 1937 Jun 8 · 1938 May 29 · 1939 Oct 12 · 1940 Apr 7 · 1940 Oct 1 · 1941 Sep 21 · 1943 Feb 4 · 1944 Jan 25 · 1945 Jul 9 · 1947 May 20 · 1948 Nov 1 · 1950 Sep 12 · 1952 Feb 25 · 1954 Jun 30 · 1955 Jun 20 · 1956 Jun 8 · 1957 Oct 23 · 1958 Oct 12 · 1959 Oct 2 · 1961 Feb 15 · 1962 Feb 5 · 1963 Jul 20 · 1965 May 30 · 1966 Nov 12 · 1967 Nov 2 · 1968 Sep 22 · 1970 Mar 7 · 1972 Jul 10 · 1973 Jun 30 · 1974 Jun 20 · 1976 Oct 23 · 1977 Oct 12 · 1979 Feb 26 · 1980 Feb 16 · 1981 Jul 31 · 1983 Jun 11 · 1984 Nov 22 · 1985 Nov 12 · 1986 Oct 3 · 1987 Mar 29 · 1988 Mar 18 · 1990 Jul 22 · 1991 Jul 11 · 1992 Jun 30 · 1994 Nov 3 · 1995 Oct 24 · 1997 Mar 9 · 1998 Feb 26 · 1999 Aug 11 · 2001 Jun 21 · 2002 Dec 4 · 2003 Nov 23 · 2005 Apr 8 · 2006 Mar 29 · 2008 Aug 1 · 2009 Jul 22 Future Total/hybrid eclipses 2010 Jul 11 · 2012 Nov 13 · 2013 Nov 3 · 2015 Mar 20 · 2016 Mar 9 · 2017 Aug 21 · 2019 Jul 2 · 2020 Dec 14 · 2021 Dec 4 · 2023 Apr 20 · 2024 Apr 8 · 2026 Aug 12 · 2027 Aug 2 · 2028 Jul 22 · 2030 Nov 25 · 2031 Nov 14 · 2033 Mar 30 · 2034 Mar 20 · 2035 Sep 2 · 2037 Jul 13 · 2038 Dec 26 · 2039 Dec 15 · 2041 Apr 30 · 2042 Apr 20 · 2043 Apr 9 · 2044 Aug 23 · 2045 Aug 12 · 2046 Aug 2 · 2048 Dec 5 · 2049 Nov 25 · 2050 May 20 · 2052 Mar 30 · 2053 Sep 12 · 2055 Jul 24 · 2057 Jan 5 · 2057 Dec 26 · 2059 May 11 · 2060 Apr 30 · 2061 Apr 20 · 2063 Aug 24 · 2064 Aug 12 · 2066 Dec 17 · 2067 Dec 6 · 2068 May 31 · 2070 Apr 11 · 2071 Sep 23 · 2072 Sep 12 · 2073 Aug 3 · 2075 Jan 16 · 2076 Jan 6 · 2077 May 22 · 2078 May 11 · 2079 May 1 · 2081 Sep 3 · 2082 Aug 24 · 2084 Dec 27 · 2086 Jun 11 · 2088 Apr 21 · 2089 Oct 4 · 2090 Sep 23 · 2091 Aug 15 · 2093 Jan 27 · 2094 Jan 16 · 2095 Jun 2 · 2096 May 22 · 2097 May 11 · 2099 Sep 14 · 2100 Sep 4 Past Annular eclipses 1854 May 26  · ... 1901 Nov 11 · 1903 Mar 29 · 1904 Mar 17 · 1905 Mar 6 · 1907 Jul 10 · 1908 Jun 28 · 1911 Oct 22 · 1914 Feb 25 · 1915 Feb 14 · 1915 Aug 10 · 1916 Jul 30 · 1917 Dec 14 · 1918 Dec 3 · 1919 Nov 22 · 1921 Apr 8 · 1922 Mar 28 · 1923 Mar 17 · 1925 Jul 20 · 1926 Jul 9 · 1927 Jan 3 · 1929 Nov 1 · 1932 Mar 7 · 1933 Feb 24 · 1933 Aug 21 · 1934 Aug 10 · 1935 Dec 25 · 1936 Dec 13 · 1937 Dec 2 · 1939 Apr 19 · 1941 Mar 27 · 1943 Aug 1 · 1944 Jul 20 · 1945 Jan 14 · 1947 Nov 12 · 1948 May 9 · 1950 Mar 18 · 1951 Mar 7 · 1951 Sep 1 · 1952 Aug 20 · 1954 Jan 5 · 1954 Dec 25 · 1955 Dec 14 · 1957 Apr 30 · 1958 Apr 19 · 1959 Apr 8 · 1961 Aug 11 · 1962 Jul 31 · 1963 Jan 25 · 1965 Nov 23 · 1966 May 20 · 1969 Mar 18 · 1969 Sep 11 · 1970 Aug 31 · 1972 Jan 16 · 1973 Jan 4 · 1973 Dec 24 · 1976 Apr 29 · 1977 Apr 18 · 1979 Aug 22 · 1980 Aug 10 · 1981 Feb 4 · 1983 Dec 4 · 1984 May 30 · 1987 Sep 23 · 1988 Sep 11 · 1990 Jan 26 · 1991 Jan 15 · 1992 Jan 4 · 1994 May 10 · 1995 Apr 29 · 1998 Aug 22 · 1999 Feb 16 · 2001 Dec 14 · 2002 Jun 10 · 2003 May 31 · 2005 Oct 3 · 2006 Sep 22 · 2008 Feb 7 · 2009 Jan 26 Future Annular eclipses 2010 Jan 15 · 2012 May 20 · 2013 May 10 · 2014 Apr 29 · 2016 Sep 1 · 2017 Feb 26 · 2019 Dec 26 · 2020 Jun 21 · 2021 Jun 10 · 2023 Oct 14 · 2024 Oct 2 · 2026 Feb 17 · 2027 Feb 6 · 2028 Jan 26 · 2030 Jun 1 · 2031 May 21 · 2032 May 9 · 2034 Sep 12 · 2035 Mar 9 · 2038 Jan 5 · 2038 Jul 2 · 2039 Jun 21 · 2041 Oct 25 · 2042 Oct 14 · 2043 Oct 3 · 2044 Feb 28 · 2045 Feb 16 · 2046 Feb 5 · 2048 Jun 11 · 2049 May 31 · 2052 Sep 22 · 2053 Mar 20 · 2056 Jan 16 · 2056 Jul 12 · 2057 Jul 1 · 2059 Nov 5 · 2060 Oct 24 · 2061 Oct 13 · 2063 Feb 28 · 2064 Feb 17 · 2066 Jun 22 · 2067 Jun 11 · 2070 Oct 4 · 2071 Mar 31 · 2074 Jan 27 · 2074 Jul 24 · 2075 Jul 13 · 2077 Nov 15 · 2078 Nov 4 · 2079 Oct 24 · 2081 Mar 10 · 2082 Feb 27 · 2084 Jul 3 · 2085 Jun 22 · 2085 Dec 16 · 2088 Oct 14 · 2089 Apr 10 · 2092 Feb 7 · 2092 Aug 3 · 2093 Jul 23 · 2095 Nov 27 · 2096 Nov 15 · 2097 Nov 4 · 2099 Mar 21 · 2100 Mar 10 Other planets Jupiter · Mars · Pluto Related topics Solar eclipses in fiction · Images v • d • e The Sun Structure Core · Radiation zone · Convection zone Atmosphere Photosphere · Chromosphere · Transition region · Corona Extended structure Heliosphere (Current sheet · Termination shock) · Heliosheath · Heliopause · Bow shock Sun-related phenomena Coronal holes · Coronal loops · Coronal mass ejections · Eclipses · Faculae · Helmet streamers · Flares · Granules · Moreton waves · Prominences and filaments · Radiation (variation) · Solar cycle (Solar maximum · Solar minimum · Sunspots) · Spicules · Supergranulation · Solar wind Related topics Solar System · Solar dynamo · Solar telescope Spectral class: G2 v • d • e The Moon Physical features Internal structure · Gravity field · Topography · Magnetic field · Atmosphere Orbit Orbit of the Moon · Phases · Solar eclipse · Lunar eclipse · Tides Lunar surface Selenography · Near side · Far side · Lunar mare · Craters · South Pole-Aitken basin · Shackleton crater · Water · Soil · Peak of eternal light · Space weathering · 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