Solar eclipse

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Solar Eclipse is also an alien friend of the rubber doll Betty Spaghetty.
File:Solar eclips 1999 4.jpg
Photo taken during the French 1999 eclipse

A solar eclipse occurs when the Moon passes in front of the Sun and obscures it totally or partially. This configuration can only exist at New Moon, when Sun, Moon and Earth are on a single line with the Moon in the middle.

There are four types of solar eclipses:

  • A partial solar eclipse occurs when the Sun is only partially overlapped by the Moon. This is similar to a (lunar) penumbral eclipse, and the part of the Earth experiencing the total eclipse is in the moon's penumbra.
  • A total solar eclipse occurs when the Moon completely obscures the Sun. This happens when the Moon is near perigee and its angular diameter as seen from Earth is identical to or slightly larger than that of the Sun. The part of the Earth experiencing the total eclipse is in the moon's umbra. A total solar eclipse is the only opportunity to observe the Sun's corona without specialised equipment.
  • An annular (ring-formed) eclipse occurs when the Moon's center passes in front of Sun's center while the Moon is near apogee. The Moon's angular diameter is then smaller than that of the Sun so that a ring of the Sun can still be seen around the Moon. The part of the Earth experiencing the total eclipse is in the moon's antumbra.
  • A hybrid eclipse occurs when the curvature of Earth's surface causes a single solar eclipse to be observed as annular from some locations but total from other locations. A total eclipse is seen from places on the Earth's surface that lie along the path of the eclipse and are physically closer to the Moon, and so intersect the Moon's umbra; other locations, further from the Moon, fall in the Moon's antumbra and the eclipse is annular.
File:Film eclipse soleil 1999.jpg
Photo taken by Luc Viatour during the French 1999 eclipse

The term "solar eclipse" is a misnomer: the phenomenon is actually an occultation. An "eclipse" occurs when one celestial object passes into the shadow cast by another (as with an eclipse of the Moon). An "occultation' occurs when one body passes in front of another. When at its new phase the Moon passes in front of, or occults, the Sun, as seen from Earth, the Moon also casts a small shadow on Earth. An "occultation" of the Sun is therefore also a partial "eclipse" of Earth.

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Photo taken during the Spanish 2005 annular eclipse

Observing a solar eclipse

Looking at the Sun is dangerous at any time when any part of the brilliant visible disk of the Sun (its photosphere) is visible; to do so can cause permanent eye damage. This is true at any time, including during solar eclipses; since an eclipse offers an unusually high temptation to look at the Sun, there is a high incidence of eye damage caused during solar eclipses. Viewing the Sun through any kind of optical aid —binoculars, a telescope, or even a camera's viewfinder— is extremely dangerous.

Safe Solar Viewing

  • NEVER look directly at the sun with binoculars or telescope etc - NEVER even look at the sun with the naked eye - Eye damage will result, which may cause permanent blindness!

The Sun can be viewed using appropriate filtration to block the harmful part of the Sun's radiation. Note that sunglasses are of little use, since they don't block the harmful and invisible infra-red radiation which causes retinal damage; other improvised methods, such as using a reflection in water, or looking through a compact disk, are equally dangerous. Only properly designed and certified solar filters should ever be used for direct viewing of the Sun; and these must be in perfect condition, as even a small defect could cause damage.

The safest way to view the Sun is by indirect projection. This can be done by projecting an image of the sun onto a white piece of paper or card using a pair of binoculars (with one of the lenses covered), a telescope, or another piece of cardboard with a small hole in it (about 1 mm diameter), often called a pinhole camera. The projected image of the sun can then be safely viewed; this technique can be used to observe sunspots, as well as eclipses. However, care must be taken to ensure that no-one looks through the projector (telescope, pinhole, etc.) directly, as this will cause severe eye damage; particular care should be taken if children are present.

It is safe to directly observe the total phase of a total solar eclipse, when the Sun's photosphere is completely covered by the Moon; indeed, this is a very beautiful sight. The Sun's faint corona will be visible, and even the chromosphere, solar prominences, and possibly even a solar flare may be visible. The danger here is of being caught out by the end of the total phase, and the return of the "exposed" Sun; because all parts of the Sun's disk are of similar intensity, even a tiny sliver of the Sun could cause permanent eye damage. For this reason, viewing the total phase of a solar eclipse through binoculars or a telescope should not be recommended.

For more information on safe eclipse viewing, see:

Eclipse frequency and cause

File:Solar eclipse.png
Diagram of solar eclipse

Total and annular eclipses both occur when the Moon lines up with the Sun exactly, but since the Moon's orbit is not perfectly circular it is sometimes farther away from Earth and doesn't always cover the entire solar disc from Earth's point of view.

It is one of the most remarkable coincidences of nature that the Sun lies approximately 400 times as far away from Earth as does the Moon, and the Sun is also approximately 400 times as large in diameter as the Moon. As a result, as seen from Earth, the Sun and the Moon appear to be nearly the same apparent size. The Moon orbits Earth in an elliptical, or elongated orbit, however, and not in a circular orbit. Thus during about 55-60% of its orbit the Moon is far enough from Earth ("apogee") that it is too small to cover the Sun's surface completely. During the remaining portion of its orbit, it is closer to Earth ("perigee") and large enough in apparent size to cover the Sun completely.

When a solar eclipse occurs near apogee, there is therefore a small ring or annulus of Sun that remains uncovered even at the moment of maxiumum eclipse. This produces an "annular" eclipse, during which the brilliant and blinding uncovered ring of the Sun makes the solar corona invisible. When a solar eclipse occurs near perigee, however, the Moon is close enough to Earth and large enough in the sky that it can cover the entire bright surface (the photosphere) of the Sun completely, and the observer sees a total eclipse, at which time the ghostly white solar corona appears.

A solar eclipse can only be seen in a band across Earth as the Moon's shadow moves across its surface, while a total or annular eclipse is actually total or ring-formed in only a small band within this band (the eclipse path), and partial elsewhere (total eclipse takes place where the umbra of the Moon's shadow falls, whereas a partial eclipse is visible where the penumbra falls). The full band is generally around 100 km in width. The eclipse path will be widest if the Moon happens to be at perigee, in which case the eclipse path alone can reach 270 km in width.

Total solar eclipses are rare events. Although they occur somewhere on Earth approximately every 18 months, it has been estimated that they recur at any given spot only every 300 to 400 years. And after waiting so long, the total solar eclipse only lasts for a few minutes, as the Moon's umbra moves eastward at over 1700 km/h. Totality can never last more than 7 min 40 s, and is usually a good deal shorter. During each millennium there are typically fewer than 10 total solar eclipses exceeding 7 minutes. The last time this happened was June 30, 1973. Those alive today probably won't live to see it happen again — on June 25, 2150. The longest total solar eclipse during the 8,000-year period from 3000 BC to 5000 AD will occur on July 16, 2186, when totality will last 7 min 29 s. (eclipse predictions by Fred Espenak, NASA/GSFC.)

For astronomers, a total solar eclipse forms a rare opportunity to observe the corona (the outer layer of the Sun's atmosphere). Normally this is not visible because the photosphere is much brighter than the corona.

Calculating the date of a solar eclipse

If you know the date and time of a solar eclipse, you can predict other eclipses using eclipse cycles. Two well-known eclipse cycles are the Saros cycle and the Inex cycle. The Saros cycle is probably the most well known, and one of the best, eclipse cycles. The Inex cycle is itself a poor cycle, but it is very convenient in the classification of eclipse cycles. After a Saros cycle finishes, a new Saros cycle begins 1 Inex later (hence its name: in-ex).

File:Total Solar Eclipse Paths- 1001-2000.gif
Total Solar Eclipse Paths: 1001-2000. This image was merged from 50 separated images from http://sunearth.gsfc.nasa.gov/eclipse/

Historical solar eclipses

In the Odyssey, XIV, 151, Homer states that Odysseus will return to his home, and take vengeance on the suitors of Penelope, at the failing of the old moon and the coming of the new. Later in the Odyssey (XX, 356-357 and 390), Homer adds that the Sun vanished out of heaven and an evil gloom covered all things about the hour of the midday meal, during the celebration of the new moon. A total eclipse of the Sun was visible from the Greek island of Ithaca on April 16, 1178 BC. This would be six years after the end of the Trojan War, as traditionally dated (1184 BC), though within the Odyssey narrative it is ten years after the war.

File:Solar Eclipse Path 16 Jun 763 BC.png
Path of the total eclipse of 763 BC described in an Assyrian text

A solar eclipse of 15 June, 763 BC mentioned in an Assyrian text is important for the Chronology of the Ancient Orient.

A double (solar and lunar) eclipse took place 23 years after the ascension of king Shulgi of Babylon. This has been identified with eclipses that occurred on 9 May (solar eclipse) and 24 May (lunar eclipse), 2138 BC . This identification is however much less commonly accepted than the eclipse of 763 BC. See also Chronology of Babylonia and Assyria.

On June 4, 780 BC a solar eclipse was recorded in China.

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

An annular eclipse of the Sun occurred at Sardis on February 17, 478 BC, while Xerxes was departing for his expedition against Greece, as Herodotus, VII, 37 recorded ([Hind and Chambers, 1889: 323] considered this absolute date more than a century ago). Herodotus (book IX, 10, book VIII, 131, and book IX, 1) reports that another solar eclipse was observed in Sparta during the next year, on August 1, 477 BC. The sky suddenly darkened in the middle of the sky, well after the battles of Thermopylae and Salamis, after the departure of Mardonius to Thessaly at the beginning of the spring of (477 BC) and his second attack on Athens, after the return of Cleombrotus to Sparta. Note that the modern conventional dates are different by a year or two, and that these two eclipse records have been ignored so far.

The foundation of Rome took place 437 years after the capture of Troy (1182 BC), according to Velleius Paterculus (VIII, 5). It took place shortly before an eclipse of the Sun that was observed at Rome on June 25, 745 BC and had a magnitude of 50.3%. Its beginning occurred at 16:38, its middle at 17:28, and its end at 18:16. Varro may have used the consular list with its mistakes, calling the year of the first consuls "245 ab urbe condita" (a.u.c.). A new study claims that the Varronian date has been superseded. Its correctness has not been proved scientifically but it is used worldwide.

According to Lucius Tarrutius of Firmum, Romulus was conceived in the womb on the 23rd day of the Egyptian month Choiac, at the time of a total eclipse of the Sun. This eclipse occurred on June 15, 763 BC, with a magnitude of 62.5% at Rome. Its beginning took place at 6:49, its middle at 7:47 and its end at 8:51. He was born on the 21st day of the month of Thoth. The first day of Thoth fell on 2 March in that year (Prof. E. J. Bickerman, 1980: 115). That implies that Rhea Silvia's pregnancy lasted for 281 days. Rome was founded on the ninth day of the month Pharmuthi, which was April 21, as universally agreed. The Romans add that, about the time Romulus started to build the city, an eclipse of the Sun was observed by Antimachus, the Teian poet, on the 30th day of the lunar month. This eclipse (see above) had a magnitude of 54.6% at Teos, Asia Minor. It started at 17:49 and was still eclipsed at sunset, at 19:20. Romulus vanished in the 54th year of his life, on the Nones of Quintilis (July), on a day when the Sun was darkened. The day turned into night, which sudden darkness was believed to be an eclipse of the Sun. It occurred on July 17, 709 BC, with a magnitude of 93.7%, beginning at 5:04 and ending at 6:57. All these eclipse data have been calculated by Prof. Aurél Ponori-Thewrewk, retired director of the Planetarium of Budapest. Plutarch placed it in the 37th year from the foundation of Rome, on the fifth of our month July, then called Quintilis, on "Caprotine Nones". Livy (I, 21) also states that Romulus ruled for 37 years. He was slain by the Senate or disappeared in the 38th year of his reign. Most of these have been recorded by Plutarch (Lives of Romulus, Numa Pompilius and Camillus), Florus (Book I, I), Cicero (The Republic VI, 22: Scipio's Dream), Dio (Dion) Cassius and Dionysius of Halicarnassus (L. 2). Dio in his Roman History (Book I) confirms these data by telling that Romulus was in his 18th year of age when he founded Rome. Therefore, three eclipse records prove that Romulus reigned from 746 BC to 709 BC.

File:IMG 1650 zonsverduistering Malta.JPG
Images of the sun during a partial eclipse through the leaves of a tree

Observations

During a solar eclipse special observations can be done with the unaided eye. Normally the spots of light which fall through the small openings between the leaves of a tree, have a circular shape. These are images of the sun. During a partial eclipse, the light spots will show the partial shape of the sun, as seen on the picture.

Special observation campaigns

Solar eclipse before sunrise or after sunset

It is possible for a solar eclipse to attain totality (or in the event of a partial eclipse, near totality) before sunrise or after sunset from a particular location. When this occurs shortly before the former or after the latter, the sky will appear much darker than it would otherwise be immediately before sunrise or after sunset. On these occasions, an object — especially a planet (often Mercury) — may be visible near the sunrise or sunset point of the horizon when it could not have been seen without the eclipse.

Simultaneous occurrence of solar eclipse and transit of a planet

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 of a Solar eclipse and a transit of Venus is expected on April 5, 15232.

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

More common — but still quite rare — is a conjunction of any planet (not confined exclusively to Mercury or Venus) concomitant with 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 (unless the line-up of it and the Sun was so exact that the Sun occulted it). At one time, some scientists — including Albert Einstein — hypothesized that there may have been a planet even closer to the Sun than Mercury; the only way to confirm its existence would have been to observe it during a total solar eclipse. When no such planet was found during such an eclipse, the possibility of its existence was ruled out.

Solar eclipses by artificial satellites

Artificial satellites can also get in the line between Earth and Sun. But none are large enough to cause an eclipse. At the altitude of the International Space Station, for example, an object would need to be about 3.35 km across to blot the Sun out entirely. This means the best you can get is a satellite transit, but these events 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. Like a transit of a planet it will not get dark. [1]

Past and future eclipses

Although there is a total eclipse visible somewhere on Earth most years, some are more conveniently observed than others. Eclipses where the path of totality crosses major population centres generate the most interest in the general public.

Selected past and upcoming eclipses are:

Selected Solar Eclipses
Date of
eclipse
Time (UTC) Type Max Duration Eclipse Path Notes
Start Mid End
1919-05-29 - - - total   West Africa Photographed by Arthur Eddington to verify general relativity
1999-08-11 - - - total - Europe, Asia
2001-06-21 - - - total 04:57 min South America, Africa
December 14, 2001 - - - annular 03:53 min North and Middle America
June 10, 2002 - - - annular 00:23 min Asia, Australia, North America
December 4, 2002 - - - total 02:04 min South Africa, Antarctica, Indonesia, Australia
May 31, 2003 - - - annular 03:37 min Europe, Asia, North America
November 23, 2003 - - - total 01:57 min Australia, New Zealand, Antarctica, South America
April 19, 2004 - - - partial - Antarctica, South Africa
October 14, 2004 - - - partial - Asia, Hawaii, Alaska
April 8, 2005 - - - hybrid 00:42 min Pacific, Middle America
2005-10-03 08:41 10:31 12:22 annular 04:32 min northern Africa, Europe, western Asia, Middle East and India [2]
2006-03-29 - - - total 04:07 min Brazil, northern Africa, central Asia, Mongolia [3]
September 22, 2006 - - - annular 07:09 min South America, West Africa, Antarctica
March 19, 2007 - - - partial - Asia, Alaska
September 11, 2007 - - - partial - South America, Antarctica
February 7, 2008 - - - annular 02:12 min Antarctica, Australia, New Zealand
August 1, 2008 - - - total 02:27 min North America, Europe, Asia
January 26, 2009 - - - annular 07:54 min Southern Africa, Antarctica, South East Asia, Australia
2009-07-22 - - - total 06:39 min India, China, Pacific Ocean, best view in Shanghai, Hangzhou or Wuhan. Longest duration of totality in the 21st century
January 15, 2010 - - - annular 11:08 min Africa, Asia
July 11, 2010 - - - total 05:20 min Southern South America, Tahiti
January 4, 2011 - - - partial - Europe, Africa, Central Asia
June 1, 2011 - - - partial - Iceland, northern North America, East Asia
July 1, 2011 - - - partial - Southern Indian Ocean
November 25, 2011 - - - partial - Southern Africa, Antarctica, Tasmania, New Zealand
May 20, 2012 - - - annular 05:46 min Pacific, Asia, North America
November 13, 2012 - - - total 04:02 min Australia, New Zealand, southern South America, southern Pacific
May 10, 2013 - - - annular 06:03 min Australia, New Zealand, Central Pacific
November 3, 2013 - - - hybrid 01:40 min Eastern America, South Europe, Africa
April 29, 2014 - - - annular 00:00 min South India, Australia, Antarctica
October 23, 2014 - - - partial - Northern Pacific, North America
March 20, 2015 - - - total 02:47 min Atlantic before England, Norway, North Pole (!)
September 13, 2015 - - - partial - South Africa, South India, Antarctica
March 9 2016 - - - total 04m09s South Asia, Pacific
September 1 2016 - - - annular 03m06s Africa
February 26 2017 - - - annular 00m44s Southern Africa, southern South America
August 21 2017 - - - total 02m40s North America
February 15 2018 - - - partial - Antarctic, southern South America
July 13 2018 - - - partial - South Australia
August 11 2018 - - - partial - Northern Europe, north Asia
January 6 2019 - - - partial - Eastern Asia
July 2 2019 - - - total 04m33s South America
December 26 2019 - - - annular 03m39s South Asia
June 21 2020 - - - annular 00m38s South Asia
December 14 2020 - - - total 02m10s South America

(*) Duration of central eclipse.

See also

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External links

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