Solar eclipse

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

A solar eclipse occurs when a portion of the Earth is engulfed in a shadow cast by the Moon which fully or partially blocks ("occults") sunlight. This occurs when the Sun, Moon and Earth are aligned. Such alignment coincides with a new moon (syzygy) indicating the Moon is closest to the ecliptic plane.[1] 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 new moon. 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. A solar eclipse can only occur when the moon is close enough to the ecliptic plane during a new moon. Special conditions must occur for the two events to coincide because the Moon's orbit crosses the ecliptic at its orbital nodes twice every draconic month (27.212220 days) while a new moon occurs one every synodic month (29.530587981 days). Solar (and lunar) eclipses therefore happen only during eclipse seasons resulting in at least two, and up to five, solar eclipses each year; no more than two of which can be total eclipses.[2][3]

Total eclipses are rare because the timing of the new moon within the eclipse season needs to be more exact for an alignment between the observer (on Earth) and the centers of the Sun and Moon. In addition, the elliptical orbit of the Moon often takes it far enough away from Earth that its apparent size is not large enough to block the 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.

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.[4][5]

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.

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.[6] This narrow track is called the path of totality.[7]
  • 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.[8]
  • 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.[8]
  • 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.[8] 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.[9] 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 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.[8]

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 slightly elliptical, as is the Earth's orbit around the Sun. The apparent sizes of the Sun and Moon therefore vary.[10] 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 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.[11]

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 extremely short in their duration at any point, at most just a few seconds at any location within just a few kilometres of the centerline of the path. Like a focal point, the width and duration of totality and annularity are near zero at the points where the changes between the two occur.[12]

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.[8] When Earth approaches its 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 closest distance to the Sun in early January.[13]

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.[14] 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.[14] The last (umbral yet) 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.[15]

Diamond ring effect at third contact, marking the end of totality. Some prominences can also be seen.

The phases observed during a total eclipse are called:[16]

  • 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.
Other Languages
Alemannisch: Sonnenfinsternis
العربية: كسوف الشمس
অসমীয়া: সূৰ্য গ্ৰহণ
asturianu: Eclís solar
Avañe'ẽ: Kuarahykañy
azərbaycanca: Günəş tutulması
Bân-lâm-gú: Sit-ji̍t
беларуская (тарашкевіца)‎: Сонечнае зацьменьне
čeština: Zatmění Slunce
davvisámegiella: Beaivvášsevnnjodeapmi
Ελληνικά: Έκλειψη Ηλίου
español: Eclipse solar
Esperanto: Suna eklipso
føroyskt: Sólarmyrking
français: Éclipse solaire
한국어: 일식
hrvatski: Pomrčina Sunca
Bahasa Indonesia: Gerhana matahari
ᐃᓄᒃᑎᑐᑦ/inuktitut: ᓯᕿᓃᖅᓯᖅᑐᖅ
íslenska: Sólmyrkvi
italiano: Eclissi solare
עברית: ליקוי חמה
Kapampangan: Lawu aldo
kaszëbsczi: Zacmienié Słuńca
Kiswahili: Kupatwa kwa Jua
Kreyòl ayisyen: Eklips solèy
kurdî: Rojgirtin
latviešu: Saules aptumsums
Lëtzebuergesch: Sonnendäischtert
مازِرونی: کسوف
Bahasa Melayu: Gerhana matahari
монгол: Нар хиртэлт
Nederlands: Zonsverduistering
नेपाली: सूर्यग्रहण
日本語: 日食
Nordfriisk: Sanjonken
norsk nynorsk: Solformørking
occitan: Eclipsi solar
Plattdüütsch: Sünndüüsternis
português: Eclipse solar
Simple English: Solar eclipse
سنڌي: سج گرهڻ
slovenčina: Zatmenie Slnka
slovenščina: Sončev mrk
Soomaaliga: Qorax madoobaad
کوردی: ڕۆژگیران
српски / srpski: Помрачење Сунца
srpskohrvatski / српскохрватски: Pomrčina Sunca
татарча/tatarça: Кояш тотылу
ئۇيغۇرچە / Uyghurche: قۇياش تۇتۇلۇشى
vèneto: Crisse solar
Tiếng Việt: Nhật thực
文言: 日食
吴语: 日食
ייִדיש: ליקוי חמה
粵語: 日食
中文: 日食