annular eclipse
   HOME

TheInfoList



A solar eclipse occurs when a portion of the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...

Earth
is engulfed in a shadow cast by the
Moon The Moon is Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distri ...

Moon
which fully or partially blocks sunlight. This occurs when the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
,
Moon The Moon is Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distri ...

Moon
and
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...

Earth
are aligned. Such alignment coincides with a new moon ( syzygy) indicating the Moon is closest to the
ecliptic plane
ecliptic plane
. In a total
eclipse ECLiPSe is a software system for the development and deployment of Constraint Programming applications, e.g. in the areas of optimization, planning, scheduling, resource allocation In economics Economics () is the social science that s ...

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 The orbital plane of a revolving body is the geometric plane in which its orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet around a star or a natural satel ...

orbital plane
, there would be total solar eclipses every new moon. However, since the Moon's orbit is
tilted
tilted
at more than 5 degrees to the
Earth's orbit around the Sun
Earth's orbit around the Sun
, its shadow usually misses Earth. A solar eclipse can occur only when the Moon is close enough to the
ecliptic plane
ecliptic plane
during a
new moon
new moon
. Special conditions must occur for the two events to coincide because the Moon's orbit crosses the ecliptic at its
orbital node An orbital node is either of the two points where an orbit intersects a plane of reference to which it is inclined. A non-inclined orbit, which is contained in the reference plane, has no nodes. Planes of reference Common planes of referenc ...
s twice every
draconic month In lunar calendars, a lunar month is the time between two successive Syzygy (astronomy), syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. This article deals with the def ...
(27.212220 days) while a new moon occurs one every
synodic month In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. This article deals with the definitions of a 'mo ...
(29.53059 days). Solar (and lunar) eclipses therefore happen only during
eclipse seasonAn eclipse season is one of only two periods during each year when eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by havi ...
s resulting in at least two, and up to five, solar eclipses each year; no more than two of which can be total eclipses. Total eclipses are rare because the timing of the
new moon
new moon
within the
eclipse seasonAn eclipse season is one of only two periods during each year when eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by havi ...
needs to be more exact for an alignment between the observer (on Earth) and the centers of the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
and
Moon The Moon is Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distri ...

Moon
. In addition, the elliptical orbit of the
Moon The Moon is Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distri ...

Moon
often takes it far enough away from
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...

Earth
that its
apparent size The angular diameter, angular size, apparent diameter, or apparent size is an angular distance Angular distance \theta (also known as angular separation, apparent distance, or apparent separation) is the angle In Euclidean geometry, an angle is ...
is not large enough to block the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
entirely. 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 full shadow or
umbra Umbra (A) and penumbra (B) The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction Diffraction refers to various phenomena that occur whe ...

umbra
. An eclipse is a
natural phenomenon Types of natural phenomena include: Weather, fog, thunder, tornadoes; biological processes, decomposition, germination seedlings, three days after germination. Germination is the process by which an organism grows from a seed or similar s ...
. However, in some ancient and modern cultures, solar eclipses were attributed to
supernatural The supernatural encompasses supposed phenomena or entities that are not subject to the . This term is attributed to , such as s, s, , and . It also includes claimed abilities embodied in or provided by such beings, including , , , , and . Th ...

supernatural
causes or regarded as bad
omen '' (1493): natural phenomena and unnatural births. An omen (also called ''portent'') is a phenomenon A phenomenon (; plural phenomena) is an observable fact or event. The term came into its modern philosophical usage through Immanuel Kant ...

omen
s. A total solar eclipse can be frightening to people who are unaware of its
astronomical Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies celestial objects and phenomena. It uses mathematics Mathematics (from Ancient Greek, Gr ...
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
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 safe to view only the total phase of a total solar eclipse with the unaided eye and without protection. This practice must be undertaken carefully, though the extreme fading of the solar brightness by a factor of over 100 times in the last minute before totality makes it obvious when totality has begun and it is for that extreme variation and the view of the solar corona that leads people to travel to the zone of totality (the partial phases span over two hours while the total phase can last only a maximum of 7.5 minutes for any one location and is usually less). People referred to as ''
eclipse chasersEclipse chasing is the pursuit of observing solar eclipses when they occur around the Earth. Solar eclipses must occur at least twice and as often as five time a year across the Earth. Total eclipses may occur multiple times every few years. A perso ...
'' or ''umbraphiles'' will travel even to remote locations to observe or witness predicted central solar eclipses.


Types

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 A corona (, in turn derived from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the f ...
to be visible. During any one eclipse, totality occurs at best only in a narrow track on the surface of Earth. This narrow track is called the path of totality. * 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 Annulus (or anulus) or annular may refer to: Human anatomy * ''Anulus fibrosus disci intervertebralis'', spinal structure * Annulus of Zinn, a.k.a. annular tendon or ''anulus tendineus communis'', around the optic nerve * Annular ligament (disam ...
, surrounding the dark disk of the Moon.Harrington, pp. 9–11 * 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. * 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 be seen only as a partial eclipse, because the
umbra Umbra (A) and penumbra (B) The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction Diffraction refers to various phenomena that occur whe ...

umbra
passes above the Earth's polar regions and never intersects the Earth's surface. 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 300px, Morning twilight: astronomical, nautical and civil stages at dawn. The apparent disk of the Sun is shown to scale. Twilight on Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life ...
. 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 always be used for safety). The Sun's distance from Earth is about 400 times the Moon's distance, and the Sun's
diameter In geometry Geometry (from the grc, γεωμετρία; ''wikt:γῆ, geo-'' "earth", ''wikt:μέτρον, -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathematics. It is concerned with properties of space ...

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 One degree (shown in red) andeighty nine degrees (shown in blue) A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol The degree symbol or degree sign, , is a typographical symbol that is use ...
in angular measure. 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 Apollo 12 (November 14–24, 1969) was the sixth crewed flight in the United States Apollo program and the second to land on the Moon. It was launched on November 14, 1969, from the Kennedy Space Center, Florida. Commander Pete Conrad, Charles ...
observed the Earth eclipse the Sun in 1969 and when the ''Cassini–Huygens, Cassini'' Space probe, probe observed :File:Saturn eclipse.jpg, Saturn eclipsing the Sun in 2006. The Moon's orbit around the Earth is slightly ellipse, elliptical, as is the Earth's orbit around the Sun. The apparent sizes of the Sun and Moon therefore vary. 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 or equal to 1.000. Conversely, an eclipse that occurs when the Moon is near its farthest distance from Earth (''i.e.,'' near its apogee) can be only 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. 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 locations nearer the midpoint, and annular at other locations nearer the beginning and end, since the sides of the Earth are slightly further away from the Moon. These eclipses are extremely narrow in their path width and relatively short in their duration at any point compared with fully total eclipses; the 2023 April 20 hybrid eclipse's totality is over a minute in duration at various points along the path of totality. Like a focus (optics), focal point, the width and duration of totality and annularity are near zero at the points where the changes between the two occur. 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. When Earth approaches its Aphelion, farthest distance from the Sun in early July, a total eclipse is somewhat more likely, whereas conditions favour an annular eclipse when Earth approaches its perihelion, closest distance to the Sun in early January.


Terminology for central eclipse

''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 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. Gamma (eclipse), Gamma is a measure of how centrally the shadow strikes. The last (umbral yet) non-central solar eclipse was Solar eclipse of April 29, 2014, on April 29, 2014. This was an annular eclipse. The next non-central total solar eclipse will be Solar eclipse of April 9, 2043, on April 9, 2043. The phases observed during a total eclipse are called: * 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

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 Umbra (A) and penumbra (B) The umbra, penumbra and antumbra are three distinct parts of a shadow, created by any light source after impinging on an opaque object. Assuming no diffraction Diffraction refers to various phenomena that occur whe ...

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 Umbra#Antumbra, antumbra, the area of shadow beyond the umbra, will see an annular eclipse. The Orbit of the Moon, 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 a new moon occurs close to one of the points (known as Orbital node, nodes) where the Moon's orbit crosses the ecliptic.Harrington, pp. 4–5 As noted above, the Moon's orbit is also ellipse, 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. The Moon orbits the Earth in approximately 27.3 days, relative to a Inertial frame of reference, 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 In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. This article deals with the definitions of a 'mo ...
and corresponds to what is commonly called the lunar month. 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 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 In lunar calendars, a lunar month is the time between two successive Syzygy (astronomy), syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. This article deals with the def ...
. 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. 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 seasonAn eclipse season is one of only two periods during each year when eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by havi ...
s, 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. 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, and is given in ranges because the apparent sizes and speeds of the Sun and Moon vary throughout the year. 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. 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.


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 rotation 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. Rare exceptions can occur in polar regions where the path may go over or near the pole, as in 2021 on Solar eclipse of June 10, 2021, June 10 and Solar eclipse of December 4, 2021, December 4. 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 wide and the duration of totality may be over 7 minutes. 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. Besselian elements are used to predict whether an eclipse will be partial, annular, or total (or annular/total), and what the eclipse circumstances will be at any given location. Calculations with Besselian elements can determine the exact shape of the umbra's shadow on the Earth's surface. But at what ''longitudes'' on the Earth's surface the shadow will fall, is a function of the Earth's rotation, and on how much that rotation has slowed down over time. A number called ΔT (timekeeping), ΔT is used in eclipse prediction to take this slowing into account. As the Earth slows, ΔT increases. ΔT for dates in the future can only be roughly estimated because the Earth's rotation is slowing irregularly. This means that, although it is possible to predict that there will be a total eclipse on a certain date in the far future, it is not possible to predict in the far future exactly at what longitudes that eclipse will be total. Historical records of eclipses allow estimates of past values of ΔT and so of the Earth's rotation.


Duration

The following factors determine the duration of a total solar eclipse (in order of decreasing importance): # The Moon being almost exactly at perigee (making its angular diameter as large as possible). # The Earth being very near apsis, aphelion (furthest away from the Sun in its elliptical orbit, making its angular diameter nearly as small as possible). # The midpoint of the eclipse being very close to the Earth's equator, where the rotational velocity is greatest. # 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). # 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 Solar eclipse of July 16, 2186, July 16, 2186 (with a maximum duration of 7 minutes 29 seconds over northern Guyana).


Occurrence and cycles

Total solar eclipses are rare events. Although they occur somewhere on Earth every 18 months on average, it is estimated that they recur at any given place only once every 360 to 410 years, on average. 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. 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. The last time an eclipse longer than 7 minutes occurred was Solar eclipse of June 30, 1973, 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. The next total eclipse exceeding seven minutes in duration will not occur until Solar eclipse of June 25, 2150, 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 Solar eclipse of July 16, 2186, July 16, 2186, when totality will last 7 min 29 s. For comparison, the longest total eclipse of the 20th century at 7 min 8 s occurred on Solar eclipse of June 20, 1955, June 20, 1955, and there are no total solar eclipses over 7 min in duration in the 21st century. It is possible to predict other eclipses using eclipse cycles. The Saros cycle, 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.


Frequency per year

Between two and five solar eclipses occur every year, with at least one per
eclipse seasonAn eclipse season is one of only two periods during each year when eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by havi ...
. 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. On average, there are about 240 solar eclipses each century.


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 or partial, and there were no annular eclipses. Due to tidal acceleration, the orbit of the Moon around the Earth becomes approximately 3.8 cm more distant each year. Millions of years in the future, the Moon will be too far away to fully occlude the Sun, and no total eclipses will occur. In the same timeframe, the Sun may become brighter, making it appear larger in size. Estimates of the time when the Moon will be unable to occlude the entire Sun when viewed from the Earth range between 650 million and 1.4 billion years in the future.


Historical eclipses

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 Assyrian eclipse, solar eclipse of June 15, 763 BC mentioned in an Assyrian people, Assyrian text is important for the chronology of the ancient Near East. There have been other claims to date earlier eclipses. The Book of Joshua 10:13 describes the sun staying still for an entire day in the sky; a group of University of Cambridge scholars concluded this to be the annular solar eclipse that occurred on 30 October 1207 BC. The Chinese king Zhong Kang supposedly beheaded two astronomers, Hsi and Ho, who failed to predict an eclipse 4,000 years ago. 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 impact event, meteor impact in the Indian Ocean on the basis of several ancient flood myths that mention a total solar eclipse. Eclipses have been interpreted as
omen '' (1493): natural phenomena and unnatural births. An omen (also called ''portent'') is a phenomenon A phenomenon (; plural phenomena) is an observable fact or event. The term came into its modern philosophical usage through Immanuel Kant ...

omen
s, or portents. The ancient Greek historian Herodotus wrote that Thales, Thales of Miletus predicted Eclipse of Thales, 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. 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, Halys river in Asia Minor. An eclipse recorded by Herodotus before Xerxes I, Xerxes departed for his expedition against Ancient Greece, Greece, 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. Alternatively, a partial eclipse was visible from Persia on October 2, 480 BC. Herodotus also reports a solar eclipse at Sparta during the Second Persian invasion of Greece. The date of the eclipse (August 1, 477 BC) does not match exactly the conventional dates for the invasion accepted by historians. Chinese records of eclipses begin at around 720 BC. The 4th century BC astronomer Shi Shen described the prediction of eclipses by using the relative positions of the Moon and Sun. Attempts have been made to establish the exact date of Good Friday by assuming that the Crucifixion darkness and eclipse, darkness described at Jesus's crucifixion was a solar eclipse. This research has not yielded conclusive results, 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. Contemporary chronicles wrote about an eclipse at the beginning of May 664 that coincided with the beginning of the plague of 664 in the British isles. In the Western hemisphere, there are few reliable records of eclipses before AD 800, until the advent of Arab and monastic observations in the early medieval period. The Cairo astronomer Ibn Yunus wrote that the calculation of eclipses was one of the many things that connect astronomy with the Islamic law, because it allowed knowing when Salat al-Kusuf, a special prayer can be made. The first recorded observation of the corona was made in Constantinople in AD 968. The first known telescopic observation of a total solar eclipse was made in France in 1706. Nine years later, English astronomer Edmund Halley accurately predicted and observed the solar eclipse of May 3, 1715. 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 Solar eclipse of July 8, 1842, 1842, and the first photograph (or daguerreotype) of a total eclipse was taken of the solar eclipse of July 28, 1851. Spectroscope observations were made of the solar eclipse of August 18, 1868, which helped to determine the chemical composition of the Sun. John Fiske (philosopher), John Fiske summed up myths about the solar eclipse like this in his 1872 book ''Myth and Myth-Makers'',


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 Solar retinopathy, 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. 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.


Partial and annular eclipses

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. 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. The safest way to view the Sun's disk is by indirect projection.Harrington, p. 25 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. 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 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.


Totality

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. 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. During this period, the Sun is too dim to be seen through filters. The Sun's faint solar corona, 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.


Eclipse chasing

A dedicated group of eclipse chasers have pursued the observation of solar eclipses when they occur around the
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wit ...

Earth
. A person who chases eclipses is known as an umbraphile, meaning shadow lover. Umbraphiles travel for eclipses and use various tools to help view the sun including solar viewer, solar viewing glasses, also known as eclipse glasses, as well as telescopes.


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 optical viewfinder of a camera can produce damage to the retina, so care is recommended. Solar filters are required for digital photography even if an optical viewfinder is not used. Using a camera's live view feature or an electronic viewfinder is safe for the human eye, but the Sun's rays could potentially irreparably damage digital image sensors unless the lens is covered by a properly designed solar filter.


Other observations

A total solar eclipse provides a rare opportunity to observe the solar corona, 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. As the light filters through leaves of trees during a partial eclipse, the overlapping leaves create natural pinholes, displaying mini eclipses on the ground. 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 occur only just prior to and after totality, when a narrow solar crescent acts as an anisotropy, anisotropic light source.


1919 observations

The observation of a total solar eclipse of May 29, 1919, helped to confirm Albert Einstein, Einstein's theory of general relativity. By comparing the apparent distance between stars in the constellation Taurus (constellation), Taurus, with and without the Sun between them, Arthur Eddington stated that the predictive power, theoretical predictions about gravitational lenses were confirmed. The observation with the Sun between the stars was possible only 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.


Gravity anomalies

There is a long history of observations of gravity-related phenomena during solar eclipses, especially during the period of totality. In 1954, and again in 1959, Maurice Allais reported observations of strange and unexplained movement during solar eclipses. The reality of this phenomenon, named the Allais effect, has remained controversial. Similarly, in 1970, Erwin Saxl, Saxl and Mildred Allen (physicist), Allen observed the sudden change in motion of a torsion pendulum; this phenomenon is called the Saxl effect. Observation during the 1997 solar eclipse by Wang ''et al.'' suggested a possible gravitational shielding effect, which generated debate. In 2002, Wang and a collaborator published detailed data analysis, which suggested that the phenomenon still remains unexplained.


Eclipses and transits

In principle, the simultaneous occurrence of a solar eclipse and a Astronomical transit, 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. More common, but still infrequent, is a astronomical conjunction, 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 (hypothetical planet), 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.


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 solar corona, 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 Lunar phase, 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

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 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. 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. The partial phase of the Solar eclipse of August 11, 1999, 1999 total eclipse was visible from Mir. 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 A corona (, in turn derived from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the f ...
.


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 synchronous grid of Continental Europe, continental Europe and National Grid (Great Britain), 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.Solar Eclipse 2015 – Impact Analysis
" pp. 3, 6–7, 13. ''European Network of Transmission System Operators for Electricity'', 19 February 2015. Accessed: 4 March 2015.
Eclipses may cause the temperature to decrease by 3 °C, with wind power potentially decreasing as winds are reduced by 0.7 m/s. In addition to the drop in light level and air temperature, animals change their behavior during totality. For example, birds and squirrels return to their nests and crickets chirp.


Recent and forthcoming solar eclipses

Eclipses occur only in the
eclipse seasonAn eclipse season is one of only two periods during each year when eclipse An eclipse is an astronomical event that occurs when an astronomical object or spacecraft is temporarily obscured, by passing into the shadow of another body or by havi ...
, when the Sun is close to either the ascending or descending Lunar node, node of the Moon. Each eclipse is separated by one, five or six lunations (
synodic month In lunar calendars, a lunar month is the time between two successive syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. This article deals with the definitions of a 'mo ...
s), 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 month In lunar calendars, a lunar month is the time between two successive Syzygy (astronomy), syzygies of the same type: new moons or full moons. The precise definition varies, especially for the beginning of the month. This article deals with the def ...
s, eclipses with similar geometry recur 223 synodic months (about 6,585.3 days) apart. This period (18 years 11.3 days) is a Saros (astronomy), 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. Saros cycles are numbered; currently, cycles 117 to 156 are active.


See also

* Lists of solar eclipses * Eclipse chasing * Lunar eclipse * Occultation * Solar eclipses in fiction * Solar eclipses on the Moon * Transit of Deimos from Mars * Transit of Phobos from Mars


Notes


References

* * * * * * *


External links


NASA Eclipse Web Site


Fred Espenak's new eclipse site

with maps and circumstances for 5000 years of solar eclipses
Detailed eclipse explanations and predictions
Hermit Eclipse
Eclipse Photography
Prof. Miroslav Druckmüller

Larry Koehn

Xavier M. Jubier

, University of South Wales
Eclipse Image Gallery
, The World at Night
Ring of Fire Eclipse: 2012
Photos * *
Solar eclipse photographs taken from the Lick Observatory from the Lick Observatory Records Digital Archive, UC Santa Cruz Library’s Digital Collections
*
Total Solar Eclipse Shadow on Earth March 09 2016
CIMSSSatelite
List of all solar eclipses

National Geographic Solar Eclipse 101 video
* {{DEFAULTSORT:Solar Eclipse Eclipses Solar eclipses,