Solar eclipse

A total solar eclipse occurs when the Moon completely covers the Sun's disk, as seen in this 1999 solar eclipse. Solar prominences can be seen along the limb (in red) as well as extensive coronal filaments.

An annular solar eclipse (above) occurs when the Moon is too far away to completely cover the Sun's disk (May 20, 2012). During a partial solar eclipse (below), the Moon blocks only part of the Sun's disk (October 23, 2014).

A solar eclipse (as seen from the planet Earth) is a type of eclipse that occurs when the Moon passes between the Sun and Earth, and when the Moon fully or partially blocks ("occults") the Sun. This can happen only at new moon when the Sun and the Moon are in conjunction as seen from Earth in an alignment referred to as syzygy. In a total eclipse, the disk of the Sun is fully obscured by the Moon. In partial and annular eclipses, only part of the Sun is obscured.

If the Moon were in a perfectly circular orbit, a little closer to the Earth, and in the same orbital plane, there would be total solar eclipses every month. However, since the Moon's orbit is tilted at more than 5 degrees to the Earth's orbit around the Sun, its shadow usually misses Earth. The Moon's orbit must cross Earth's ecliptic plane in order for an eclipse (both solar as well as lunar) to occur. In addition, the Moon's actual orbit is elliptical, often taking it far enough away from Earth that its apparent size is not large enough to block the Sun entirely. The orbital planes cross each other at a line of nodes resulting in at least two, and up to five, solar eclipses occurring each year; no more than two of which can be total eclipses.^[1][2] However, total solar eclipses are rare at any particular location because totality exists only along a narrow path on the Earth's surface traced by the Moon's shadow or umbra.

An eclipse is a natural phenomenon. However, in some ancient and modern cultures, solar eclipses were attributed to supernatural causes or regarded as bad omens. A total solar eclipse can be frightening to people who are unaware of its astronomical explanation, as the Sun seems to disappear during the day and the sky darkens in a matter of minutes.

Since looking directly at the Sun can lead to permanent eye damage or blindness, special eye protection or indirect viewing techniques are used when viewing a solar eclipse. It is technically safe to view only the total phase of a total solar eclipse with the unaided eye and without protection; however, this is a dangerous practice, as most people are not trained to recognize the phases of an eclipse, which can span over two hours while the total phase can only last a maximum of 7.5 minutes for any one location. People referred to as eclipse chasers or umbraphiles will travel to remote locations to observe or witness predicted central solar eclipses.^[3][4]

For the dates of the next eclipses see the section Recent and forthcoming solar eclipses.

Types

Partial and annular phases of solar eclipse on May 20, 2012

Comparison of minimum and maximum apparent sizes of the Sun and Moon (and planets). An annular eclipse can occur when the Sun has a larger apparent size than the Moon, whereas a total eclipse can occur when the Moon has a larger apparent size.

Partial solar eclipse during annular solar eclipse of May 20, 2012

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 solar corona to be visible. During any one eclipse, totality occurs at best only in a narrow track on the surface of Earth.^[5]
• An annular eclipse occurs when the Sun and Moon are exactly in line with the Earth, 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 dark disk of the Moon.^[6]
• A hybrid eclipse (also called annular/total eclipse) shifts between a total and annular eclipse. At certain points on the surface of Earth, it appears as a total eclipse, whereas at other points it appears as annular. Hybrid eclipses are comparatively rare.^[6]
• A partial eclipse occurs when the Sun and Moon are not exactly in line with the Earth 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.^[6] Partial eclipses are virtually unnoticeable in terms of the sun's brightness, as it takes well over 90% coverage to notice any darkening at all. Even at 99%, it would be no darker than civil twilight.^[7] Of course, partial eclipses (and partial stages of other eclipses) can be observed if one is viewing the sun through a darkening filter (which should anyhow be used for safety).

The Sun's distance from 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.^[6]

A separate category of solar eclipses is that of the Sun being occluded by a body other than the Earth's moon, as can be observed at points in space away from the Earth's surface. Two examples are when the crew of Apollo 12 observed the Earth eclipse the Sun in 1969 and when the Cassini probe observed Saturn eclipsing the Sun in 2006.

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.^[8] 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 that occurs when the Moon is near its closest distance to Earth (i.e., near its perigee) can be a total eclipse because the Moon will appear to be large enough to completely cover 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 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 less to greater than one, so the eclipse appears to be total at some locations on Earth and annular at other locations.^[9]

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 size of the Sun in the same way, but not as much as does the Moon's varying distance from Earth.^[6] When Earth approaches its farthest distance from the Sun in July, a total eclipse is somewhat more likely, whereas conditions favour an annular eclipse when Earth approaches its closest distance to the Sun in January.^[10]

Terminology for central eclipse

Each icon shows the view from the centre of its black spot, representing the moon (not to scale)

Central eclipse is often used as a generic term for a total, annular, or hybrid eclipse.^[11] 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 the Earth (thus creating an annular or total eclipse), but not its central line. This is then called a non-central total or annular eclipse.^[11] The last non-central solar eclipse was on April 29, 2014. This was an annular eclipse. The next non-central total solar eclipse will be on April 9, 2043.^[12]

The phases observed during a total eclipse are called:^[13]

• First contact—when the Moon's limb (edge) is exactly tangential to the Sun's limb.
• Second contact—starting with Baily's Beads (caused by light shining through valleys on the Moon's surface) and the diamond ring effect. Almost the entire disk is covered.
• Totality—the Moon obscures the entire disk of the Sun and only the solar corona is visible.
• Third contact—when the first bright light becomes visible and the Moon's shadow is moving away from the observer. Again a diamond ring may be observed.
• Fourth contact—when the trailing edge of the Moon ceases to overlap with the solar disk and the eclipse ends.

Predictions

Geometry

Geometry of a total solar eclipse (not to scale)

The diagrams to the right show the alignment of the Sun, Moon, and Earth during a solar eclipse. The dark gray region between the Moon and Earth is the umbra, where the Sun is completely obscured by the Moon. The small area where the umbra touches Earth's surface is where a total eclipse can be seen. The larger light gray area is the penumbra, in which a partial eclipse can be seen. An observer in the antumbra, the area of shadow beyond the umbra, will see an annular eclipse.^[14]

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 to the north or south of the Sun. A solar eclipse can occur only when new moon occurs close to one of the points (known as nodes) where the Moon's orbit crosses the ecliptic.^[15]

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 as seen from the Earth, 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.^[16][17]

	Moon		Sun
	At perigee (nearest)	At apogee (farthest)	At perihelion (nearest)	At aphelion (farthest)
Mean radius	1,737.10 km (1,079.38 mi)		696,000 km (432,000 mi)
Distance	363,104 km (225,622 mi)	405,696 km (252,088 mi)	147,098,070 km (91,402,500 mi)	152,097,700 km (94,509,100 mi)
Angular diameter[18]	33' 30" (0.5583°)	29' 26" (0.4905°)	32' 42" (0.5450°)	31' 36" (0.5267°)
Apparent size to scale
Order by decreasing apparent size	1st	4th	2nd	3rd

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, 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.^[15]

The Moon crosses from south to north of the ecliptic at its ascending node, and vice versa at its descending node.^[15] 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 regression 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 nodical or draconic month.^[19]

Finally, the Moon's perigee is moving forwards or precessing in its orbit and makes a complete circuit in 8.85 years. The time between one perigee and the next is slightly longer than the sidereal month and known as the anomalistic month.^[20]

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 (173.3 days) apart, known as eclipse seasons, 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 to eclipse the Sun on both occasions in two partial eclipses. This means that, in any given year, there will always be at least two solar eclipses, and there can be as many as five.^[21]

Eclipses can occur only when the Sun is within about 15 to 18 degrees of a node, (10 to 12 degrees for central eclipses). This is referred to as an eclipse limit. In the time it takes for the Moon to return to a node (draconic month), the apparent position of the Sun has moved about 29 degrees, relative to the nodes.^[1] Since the eclipse limit creates a window of opportunity of up to 36 degrees (24 degrees for central eclipses), it is possible for partial eclipses (or rarely a partial and a central eclipse) to occur in consecutive months.^[22][23]

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, at about 28 km/min at the Equator, but as the Moon is moving in the same direction as the Earth's spin at about 61 km/min, the umbra almost always appears to move in a roughly west-east direction across a map of the Earth at the speed of the Moon's orbital velocity minus the Earth's rotational velocity.^[24]

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 up to 267 km (166 mi) wide and the duration of totality may be over 7 minutes.^[25] Outside of the central track, a partial eclipse is seen over a much larger area of the Earth. Typically, the umbra is 100–160 km wide, while the penumbral diameter is in excess of 6400 km.^[26]

Duration

The following factors determine the duration of a total solar eclipse (in order of decreasing importance):^[27][28]

1. The moon being almost exactly at perigee (making its angular diameter as large as possible).
2. The earth being very near aphelion (furthest away from the sun in its elliptical orbit, making its angular diameter nearly as small as possible).
3. The midpoint of the eclipse being very close to the earth's equator, where the orbital velocity is greatest.
4. The vector of the eclipse path at the midpoint of the eclipse aligning with the vector of the earth's rotation (i.e. not diagonal but due east).
5. The midpoint of the eclipse being near the subsolar point (the part of the earth closest to the sun).

The longest eclipse that has been calculated thus far is the eclipse of July 16, 2186 (with a maximum duration of 7 minutes 4 seconds over northern Guyana).

Occurrence and cycles

Total Solar Eclipse Paths: 1001–2000, showing that total solar eclipses occur almost everywhere on Earth. This image was merged from 50 separate images from NASA.^[29]

Total solar eclipses are rare events. Although they occur somewhere on Earth every 18 months on average,^[30] it is estimated that they recur at any given place only once every 360 to 410 years, on average.^[31] The total eclipse lasts for only a maximum of a few minutes at any location, because the Moon's umbra moves eastward at over 1700 km/h.^[32] Totality currently can never last more than 7 min 32 s. This value changes over the millennia and is currently decreasing. By the 8th millennium, the longest theoretically possible total eclipse will be less than 7 min 2 s.^[27] The last time an eclipse longer than 7 minutes occurred was June 30, 1973 (7 min 3 sec). Observers aboard a Concorde supersonic aircraft were able to stretch totality for this eclipse to about 74 minutes by flying along the path of the Moon's umbra.^[33] The next total eclipse exceeding seven minutes in duration will not occur until June 25, 2150. The longest total solar eclipse during the 11,000 year period from 3000 BC to at least 8000 AD will occur on July 16, 2186, when totality will last 7 min 29 s.^[27][34] For comparison, the longest total eclipse of the 20th century at 7 min 8 s occurred on June 20, 1955, and there are no total solar eclipses over 7 min in duration in the 21st century.^[35]

If the date and time of any solar eclipse are known, it is possible to predict other eclipses using eclipse cycles. The saros is probably the best known and one of the most accurate. A saros 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 westward shift of about 120° in longitude (due to the 0.3 days) and a little in latitude (north-south for odd-numbered cycles, the reverse for even-numbered ones). 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 with a partial eclipse at the opposite polar region. A saros series lasts 1226 to 1550 years and 69 to 87 eclipses, with about 40 to 60 of them being central.^[36]

Frequency per year

Between two and five solar eclipses occur every year, with at least one per eclipse season. Since the Gregorian calendar was instituted in 1582, years that have had five solar eclipses were 1693, 1758, 1805, 1823, 1870, and 1935. The next occurrence will be 2206.^[37] On average, there are about 240 solar eclipses each century.^[38]

The 5 solar eclipses of 1935

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

Final totality

Total solar eclipses are seen on Earth because of a fortuitous combination of circumstances. Even on Earth, the diversity of eclipses familiar to people today is a temporary (on a geological time scale) phenomenon. Hundreds of millions of years in the past, the Moon was closer to the Earth and therefore apparently larger, so every solar eclipse was total and there were no annular eclipses. Over a billion years in the future, the Moon will be too far away to fully occlude the Sun, and no total eclipses will occur.^[39]

Due to tidal acceleration, the orbit of the Moon around the Earth becomes about 2.2 cm more distant each year. It is estimated that, in slightly less than 1.4 billion years, the distance from the Earth to the Moon will have increased by 30,400 km. During that period, the apparent angular diameter of the Moon will decrease in size, meaning that it will no longer be able to completely cover the Sun's disk as seen from the Earth. This will be true even when the Moon is at perigee, and the Earth at aphelion. Moreover, the Sun is increasing in diameter by about 5% per billion years.^[40] Therefore, the last total solar eclipse on Earth will occur about six hundred million years from now.^[39]

Historical eclipses

Astronomers Studying an Eclipse painted by Antoine Caron in 1571

Historical eclipses are a very valuable resource for historians, in that they allow a few historical events to be dated precisely, from which other dates and ancient calendars may be deduced. A solar eclipse of June 15, 763 BC mentioned in an Assyrian text is important for the Chronology of the Ancient Orient.^[41] There have been other claims to date earlier eclipses. The King Zhong Kang supposedly beheaded two astronomers, Hsi and Ho, who failed to predict an eclipse 4,000 years ago.^[42] Perhaps the earliest still-unproven claim is that of archaeologist Bruce Masse, who putatively links an eclipse that occurred on May 10, 2807 BC with a possible meteor impact in the Indian Ocean on the basis of several ancient flood myths that mention a total solar eclipse.^[43]

Eclipses have been interpreted as omens, or portents.^[44] The ancient Greek historian Herodotus wrote that Thales of Miletus predicted an eclipse that occurred during a battle between the Medes and the Lydians. Both sides put down their weapons and declared peace as a result of the eclipse.^[45] The exact eclipse involved remains uncertain, although the issue has been studied by hundreds of ancient and modern authorities. One likely candidate took place on May 28, 585 BC, probably near the Halys river in Asia Minor.^[46] An eclipse recorded by Herodotus before Xerxes departed for his expedition against Greece,^[47] which is traditionally dated to 480 BC, was matched by John Russell Hind to an annular eclipse of the Sun at Sardis on February 17, 478 BC.^[48] Alternatively, a partial eclipse was visible from Persia on October 2, 480 BC.^[49] Herodotus also reports a solar eclipse at Sparta during the Second Persian invasion of Greece.^[50] The date of the eclipse (August 1, 477 BC) does not match exactly the conventional dates for the invasion accepted by historians.^[51]

Chinese records of eclipses begin at around 720 BC.^[52] The 4th century BC astronomer Shi Shen described the prediction of eclipses by using the relative positions of the Moon and Sun.^[53] The "radiating influence" theory (i.e., the Moon's light was reflection from the Sun) was existent in Chinese thought from about the sixth century BC (in the Zhi Ran of Zhi Ni Zi),^[54] though it was opposed by the 1st century AD philosopher Wang Chong, who made clear in his writing that this theory was nothing new.^[53] Ancient Greeks, such as Parmenides and Aristotle, also supported the theory of the Moon shining because of reflected light.^[54]

Attempts have been made to establish the exact date of Good Friday by assuming that the darkness described at Jesus's crucifixion was a solar eclipse. This research has not yielded conclusive results,^[55][56] and Good Friday is recorded as being at Passover, which is held at the time of a full moon. Further, the darkness lasted from the sixth hour to the ninth, or three hours, which is much, much longer than the eight-minute upper limit for any solar eclipse's totality. In the Western hemisphere, there are few reliable records of eclipses before 800 AD, until the advent of Arab and monastic observations in the early medieval period.^[52] The first recorded observation of the corona was made in Constantinople in 968 AD.^[49][52]

The first known telescopic observation of a total solar eclipse was made in France in 1706.^[52] Nine years later, English astronomer Edmund Halley accurately predicted and observed the solar eclipse of May 3, 1715.^[49][52] By the mid-19th century, scientific understanding of the Sun was improving through observations of the Sun's corona during solar eclipses. The corona was identified as part of the Sun's atmosphere in 1842, and the first photograph (or daguerreotype) of a total eclipse was taken of the solar eclipse of July 28, 1851.^[49] Spectroscope observations were made of the solar eclipse of August 18, 1868, which helped to determine the chemical composition of the Sun.^[49]

John Fiske summed up myths about the solar eclipse like this in his 1872 book Myth and Myth-Makers,

the myth of Hercules and Cacus, the fundamental idea is the victory of the solar god over the robber who steals the light. Now whether the robber carries off the light in the evening when Indra has gone to sleep, or boldly rears his black form against the sky during the daytime, causing darkness to spread over the earth, would make little difference to the framers of the myth. To a chicken a solar eclipse is the same thing as nightfall, and he goes to roost accordingly. Why, then, should the primitive thinker have made a distinction between the darkening of the sky caused by black clouds and that caused by the rotation of the earth? He had no more conception of the scientific explanation of these phenomena than the chicken has of the scientific explanation of an eclipse. For him it was enough to know that the solar radiance was stolen, in the one case as in the other, and to suspect that the same demon was to blame for both robberies.^[57]

Viewing

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 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.^[58][59]

Under normal conditions, the Sun is so bright that it is difficult to stare at it directly. However, during an eclipse, with so much of the Sun covered, it is easier and more tempting to stare at it. Looking at the Sun during an eclipse is 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 and can cause irreversible eye damage within a fraction of a second.^[60][61]

Partial and annular eclipses

Eclipse glasses

Pinhole projection method of observing partial solar eclipse. Insert (upper left): partially eclipsed Sun photographed with a white solar filter. Main image: projections of the partially eclipsed Sun (bottom right)

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 be used for direct viewing of the Sun's disk.^[62] Especially, self-made filters using common objects such as a floppy disk removed from its case, a Compact Disc, a black colour slide film, smoked glass, etc. must be avoided.^[63][64]

The safest way to view the Sun's disk is by indirect projection.^[65] 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. Care must be taken, however, to ensure that no one looks through the projector (telescope, pinhole, etc.) directly.^[66] 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.^[64] 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 corona or nearly complete darkening of the sky, however, depending on how much of the Sun's disk is obscured, some darkening may be noticeable. If three-quarters 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.^[67]

Totality

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 the Earth through lunar valleys. Totality then begins with the diamond ring effect, the last bright flash of sunlight.^[68]

It is safe to observe the total phase of a solar eclipse directly only when the Sun's photosphere is completely covered by the Moon, and not before or after totality.^[65] 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. At the end of totality, the same effects will occur in reverse order, and on the opposite side of the Moon.^[68]

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 long focus lens is needed (at least 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 recommended.^[69]

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 three minutes.

A total solar eclipse provides 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 may appear small and symmetric, or large and fuzzy. It is very hard to predict this in advance.^[70]

Phenomena associated with eclipses include 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, when a narrow solar crescent acts as an anisotropic light source.^[71]

1919 observations

Eddington's original photograph of the 1919 eclipse, which provided evidence for 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 stars in the constellation Taurus, with and without the Sun between them, Arthur Eddington stated that the theoretical predictions about gravitational lenses were confirmed.^[72] The observation with the Sun between the stars was only possible during totality since the stars are then visible. Though Eddington's observations were near the experimental limits of accuracy at the time, work in the later half of the 20th century confirmed his results.^[73][74]

Gravity anomalies

There is a long history of observations of gravity-related phenomena during solar eclipses, especially around totality. In 1954, and again in 1959, Maurice Allais reported observations of strange and unexplained movement during solar eclipses.^[75] This phenomenon is now called the Allais effect. Similarly, in 1970, Saxl and Allen observed the sudden change in motion of a torsion pendulum; this phenomenon is called the Saxl effect.^[76]

A recent published observation during the 1997 solar eclipse by Wang et al. suggested a possible gravitational shielding effect,^[77] which generated debate. Later in 2002, Yang and Wang published detailed data analysis, which suggested that the phenomenon still remains unexplained.^[78]

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.^[79]

More common, but still infrequent, is a conjunction of a planet (especially, but 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 in transit or during a total solar eclipse. No such planet was ever found, and general relativity has since explained the observations that led astronomers to suggest that Vulcan might exist.^[80]

Earthshine

During a total solar eclipse, the Moon's shadow covers only a small fraction of the Earth. The Earth continues to receive at least 92 percent of the amount of sunlight it receives without an eclipse – more if the penumbra of the Moon's shadow partly misses the Earth. Seen from the Moon, the Earth during a total solar eclipse is mostly brilliantly illuminated, with only a small dark patch showing the Moon's shadow. The brilliantly-lit Earth reflects a lot of light to the Moon. If the corona of the eclipsed Sun were not present, the Moon, illuminated by earthlight, would be easily visible from Earth. This would be essentially the same as the earthshine which can frequently be seen when the Moon's phase is a narrow crescent. In reality, the corona, though much less brilliant than the Sun's photosphere, is much brighter than the Moon illuminated by earthlight. Therefore, by contrast, the Moon during a total solar eclipse appears to be black, with the corona surrounding it.

Artificial satellites

From space, the Moon's shadow during a solar eclipse appears as a dark spot moving across the Earth.

The Moon's shadow over Turkey and Cyprus, seen from the ISS during a 2006 total solar eclipse.

Artificial satellites can also pass in front of the Sun as seen from the Earth, but none is 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 (2.08 mi) 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.^[81]

Observations of eclipses from spacecraft or artificial satellites orbiting above the Earth's atmosphere are not subject to weather conditions. The crew of Gemini 12 observed a total solar eclipse from space in 1966.^[82] The partial phase of the 1999 total eclipse was visible from Mir.^[83]

During the Apollo–Soyuz Test Project conducted in July 1975, the Apollo spacecraft was positioned to create an artificial solar eclipse giving the Soyuz crew an opportunity to photograph the solar corona.

Impact

The solar eclipse of March 20, 2015, was the first occurrence of an eclipse estimated to potentially have a significant impact on the power system, with the electricity sector taking measures to mitigate any impact. The continental Europe and Great Britain synchronous areas were estimated to have about 90 Gigawatts of solar power and it was estimated that production would temporarily decrease by up to 34 GW compared to a clear sky day.^[84][85] The temperature may decrease by 3 °C, and wind power potentially decreases as winds are reduced by 0.7 m/s.^[86]

Recent and forthcoming solar eclipses

Eclipse path for total and hybrid eclipses from 2001 to 2020.

Eclipses only occur in the eclipse season, when the Sun is close to either the ascending or descending node of the Moon. Each eclipse is separated by one, five or six lunations (synodic months), and the midpoint of each season is separated by 173.3 days, which is the mean time for the Sun to travel from one node to the next. The period is a little less than half a calendar year because the lunar nodes slowly regress. Because 223 synodic months is roughly equal to 239 anomalistic months and 242 draconic months, eclipses with similar geometry recur 223 synodic months (about 6,585.3 days) apart. This period (18 years 11.3 days) is a saros. Because 223 synodic months is not identical to 239 anomalistic months or 242 draconic months, saros cycles do not endlessly repeat. Each cycle begins with the Moon's shadow crossing the earth near the north or south pole, and subsequent events progress toward the other pole until the Moon's shadow misses the earth and the series ends.^[22] Saros cycles are numbered; currently, cycles 117 to 156 are active.

See also

Notes

References

• Harrington, Philip S. (1997). Eclipse! The What, Where, When, Why and How Guide to Watching Solar and Lunar Eclipses. New York: John Wiley and Sons. ISBN 0-471-12795-7. 
• Mobberley, Martin (2007). Total Solar Eclipses and How to Observe Them. Astronomers' Observing Guides. New York: Springer. ISBN 978-0-387-69827-4. 
• Steel, Duncan (1999). Eclipse: The celestial phenomenon which has changed the course of history. London: Headline. ISBN 0-7472-7385-5. 

External links

Wikimedia Commons has media related to Solar eclipse.

Wikivoyage has a travel guide for Solar eclipses.

• NASA Eclipse Web Site
• Eclipsewise, Fred Espenak's new eclipse site
• Detailed eclipse explanations and predictions, Hermit Eclipse
• Eclipse Photography, Prof. Miroslav Druckmüller
• Animated maps of August 21, 2017 solar eclipses, Larry Koehn
• Five Millennium (−1999 to +3000) Canon of Solar Eclipses Database, Xavier M. Jubier
• Animated explanation of the mechanics of a solar eclipse, University of South Wales
• Eclipse Image Gallery, The World at Night
• Ring of Fire Eclipse: 2012, Photos
•  "Sun, Eclipses of the". Collier's New Encyclopedia. 1921. 
• Centered and aligned video recording of Total Solar Eclipse 20th March 2015 on YouTube
• Solar eclipse photographs taken from the Lick Observatory from the Lick Observatory Records Digital Archive, UC Santa Cruz Library’s Digital Collections
• Video with Total Solar Eclipse March 09 2016 (From the Beginning to the Total Phase) on YouTube
• Total Solar Eclipse Shadow on Earth March 09 2016 CIMSSSatelite
• List of all solar eclipses in the United States
• Wikiversity has a solar eclipse lab that students can do on any sunny day.

Solar eclipses
Lists of eclipses	By century Antiquity 20th BC 19th BC 18th BC 17th BC 16th BC 15th BC 14th BC 13th BC 12th BC 11th BC 10th BC 9th BC 8th BC 7th BC 6th BC 5th BC 4th BC 3rd BC 2nd BC 1st BC 1st 2nd 3rd 4th 5th 6th 7th 8th 9th 10th 11th 12th 13th 14th 15th 16th 17th 18th 19th 20th 21st 22nd 23rd 24th 25th 26th 27th 28th 29th 30th Saros series 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 Visibility China United Kingdom Philippines United States Historical Mursili's eclipse (1312 BC) Assyrian eclipse (763 BC) Eclipse of Thales (585 BC)
Total/hybrid eclipses → symbol denotes next total/hybrid eclipse	1560 Aug 21 1598 Mar 7 1652 Apr 8 1654 Aug 12 1673 Aug 12 1699 Sep 23 1715 May 3 1724 May 22 1766 Feb 9 1778 Jun 24 1780 Oct 27 1806 Jun 16 1816 Nov 19 1824 Jun 26 1842 Jul 8 1851 Jul 28 1853 Nov 30 1857 Mar 25 1858 Sep 7 1860 Jul 18 1865 Apr 25 1867 Aug 29 1868 Aug 18 1869 Aug 7 1870 Dec 22 1871 Dec 12 1874 Apr 16 1875 Apr 6 1878 Jul 29 1882 May 17 1883 May 6 1885 Sep 8 1886 Aug 29 1887 Aug 19 1889 Jan 1 1889 Dec 22 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 Oct 1 1941 Sep 21 1943 Feb 4 1944 Jan 25 1944 Jul 20 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 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 2114 Jun 3 2132 Jun 13 2150 Jun 25 2168 Jul 5 2186 Jul 16
Annular eclipses → symbol denotes next annular eclipse	1820 Sep 7 1854 May 26 1879 Jan 22 1889 Jun 28 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 1940 Apr 7 1941 Mar 27 1943 Aug 1 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 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
Partial eclipses → symbol denotes next partial eclipse	1902 Apr 8 1902 May 7 1902 Oct 31 1906 Feb 23 1906 Jul 21 1906 Aug 20 1909 Dec 12 1910 Nov 2 1913 Apr 6 1913 Aug 31 1913 Sep 30 1916 Dec 24 1917 Jan 23 1917 Jun 19 1917 Jul 19 1920 May 18 1920 Nov 10 1924 Mar 5 1924 Jul 31 1924 Aug 30 1927 Dec 24 1928 Jun 17 1928 Nov 12 1931 Apr 18 1931 Sep 12 1931 Oct 11 1935 Jan 5 1935 Feb 3 1935 Jun 30 1935 Jul 30 1938 Nov 21 1942 Mar 16 1942 Aug 12 1942 Sep 10 1946 Jan 3 1946 May 30 1946 Jun 29 1946 Nov 23 1949 Apr 28 1949 Oct 21 1953 Feb 14 1953 Jul 11 1953 Aug 9 1956 Dec 2 1960 Mar 27 1960 Sep 20 1964 Jan 14 1964 Jun 10 1964 Jul 9 1964 Dec 4 1967 May 9 1968 Mar 28 1971 Feb 25 1971 Jul 22 1971 Aug 20 1974 Dec 13 1975 May 11 1975 Nov 3 1978 Apr 7 1978 Oct 2 1982 Jan 25 1982 Jun 21 1982 Jul 20 1982 Dec 15 1985 May 19 1986 Apr 9 1989 Mar 7 1989 Aug 31 1992 Dec 24 1993 May 21 1993 Nov 13 1996 Apr 17 1996 Oct 12 1997 Sep 2 2000 Feb 5 2000 Jul 1 2000 Jul 31 2000 Dec 25 2004 Apr 19 2004 Oct 14 2007 Mar 19 2011 Jan 4 2011 Jun 1 2011 Jul 1 2011 Nov 25 2014 Oct 23 2015 Sep 13 → 2018 Feb 15 2018 Jul 13 2018 Aug 11 2019 Jan 6 2022 Apr 30 2022 Oct 25 2025 Mar 29 2025 Sep 21 2029 Jan 14 2029 Jun 12 2029 Jul 11 2032 Nov 3 2033 Sep 23 2036 Feb 27 2036 Jul 23 2036 Aug 21 2037 Jan 16 2040 May 11 2040 Nov 4 2047 Jan 26 2047 Jun 23 2047 Jul 22 2047 Dec 16 2050 Nov 14 2051 Apr 11 2051 Oct 4 2054 Mar 9 2054 Aug 3 2054 Sep 2 2055 Jan 27 2058 May 22 2058 Jun 21 2058 Nov 16 2062 Mar 11 2062 Sep 3 2065 Feb 5 2065 Jul 3 2065 Aug 2 2065 Dec 27 2068 Nov 24 2069 Apr 21 2069 May 20 2069 Oct 15 2072 Mar 19 2073 Feb 7 2076 Jun 1 2076 Jul 1 2076 Nov 26 2083 Feb 16 2083 Jul 15 2083 Aug 13 2084 Jan 7 2086 Dec 6 2087 May 2 2087 Jun 1 2087 Oct 26 2090 Mar 31 2091 Feb 18 2094 Jun 13 2094 Jul 12 2094 Dec 7 2098 Apr 1 2098 Sep 25 2098 Oct 24
Other bodies	Mars Moon Jupiter Neptune Pluto Saturn Uranus
Related topics	Solar eclipses in fiction
Book Category Commons Portal WikiProject

The Sun
Internal structure	Core Radiation zone Tachocline Convection zone
Atmosphere	Photosphere Supergranulation Granule Faculae Sunspot Chromosphere Plage Spicule Moreton wave Corona Transition region Coronal hole Coronal loop Coronal mass ejection Prominence Helmet streamer Supra-arcade downflows
Variation	Solar cycle List of solar cycles Solar maximum Solar minimum Wolf number Solar wind Flare Helioseismology
Heliosphere	Current sheet Termination shock Heliosheath Heliopause Bow shock
Related topics	Solar activity Solar astronomy Solar dynamo Eclipse Solar energy Solar observation Solar physics Solar System Solar telescope Solar time Standard solar model Radiation Solar neutrino
Spectral class: G2V

The Moon
Physical features	Face on the Moon Internal structure Gravity field Topography Magnetic field Atmosphere Ion tail Moonlight Lunar swirls
Orbit	Orbit of the Moon Phases Lunation Lunar libration Full Moon Lunar terminator Full moon cycle Earthshine Lunar eclipse Solar eclipse Solar eclipses on the Moon Tide
Surface	Selenography Near side Far side North pole South pole Lunar mare List Craters List Calderas Mountains Valleys Volcanic features South Pole–Aitken basin Shackleton crater Water Soil Ray systems Peak of eternal light Crater of eternal darkness Space weathering Transient lunar phenomenon Lunar basalt 70017
Science	Geology timescale Giant-impact hypothesis Hill sphere Moon rocks Lunar meteorites KREEP Late Heavy Bombardment Lunar laser ranging ALSEP Observation Origin Lunar sample displays Apollo 11 lunar sample display Apollo 17 lunar sample display
Exploration	Apollo program Exploration of the Moon Colonization of the Moon List of lunar probes List of missions to the Moon Moon landing conspiracy theories
Related topics	Lunar calendar Lunisolar calendar Craters named after people Double planet Lunar effect Man in the Moon Memorials on the Moon Month Lunar month Moon illusion Harvest moon Hunter's moon Moon in art and literature Moon in mythology Hjúki and Bil (Norse legends) Moon is made of green cheese Natural satellite Solar System Supermoon Theia Tourism
Phases / Occurrence	Black moon Blue moon Lunar phase New moon Dark moon Wet moon Lilith (hypothetical moon)
Category Moon portal Earth sciences portal Solar System portal