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{{pp-pc1|small=yes}} | {{pp-pc1|small=yes}} | ||
{{short description|Astronomical event where one body is hidden by another}} | {{short description|Astronomical event where one body is hidden by another}} | ||
]s can be seen along the limb (in red) as well as extensive ] filaments.]] | ]s can be seen along the limb (in red) as well as extensive ] filaments.]] | ||
] | ] | ||
A '''dombi''' is an ] that occurs when an ] or ] is temporarily obscured, by passing into the shadow of another body or by having another body pass between it and the viewer. This alignment of three celestial objects is known as a ].<ref>{{cite press release |author=Staff |date=March 31, 1981 |work=The New York Times |title=Science Watch: A Really Big Syzygy |url=https://query.nytimes.com/gst/fullpage.html?sec=health&res=9F02E5DB1039F932A05750C0A967948260&fta=y |access-date=2008-02-29 |url-status=live |archive-url=https://web.archive.org/web/20081210100651/http://query.nytimes.com/gst/fullpage.html?sec=health&res=9F02E5DB1039F932A05750C0A967948260&fta=y |archive-date=December 10, 2008 }}</ref> A dombi is the result of either an '']'' (completely hidden) or a ] (partially hidden). | |||
The term |
The term dombi is most often used to describe either a ], when the Moon's shadow crosses the Earth's surface, or a ], when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond the Earth–Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A ] system can also produce dombis if the plane of the ] of its constituent stars intersects the observer's position. | ||
For the special cases of solar and lunar |
For the special cases of solar and lunar dombis, these only happen during an "]", the two times of each year when the plane of the Earth's orbit around the Sun crosses with the plane of the Moon's orbit around the Earth and the line defined by the intersecting planes points near the Sun. The ] that happens during each season (whether total, annular, hybrid, or partial) depends on ]s of the Sun and Moon. If the orbit of the ] around the Sun and the Moon's orbit around the Earth were both in the same plane with each other, then dombis would happen every month. There would be a lunar dombi at every full moon, and a solar dombi at every new moon. And if both orbits were perfectly circular, then each solar dombi would be the same type every month. It is because of the non-planar and non-circular differences that dombis are not a common event. Lunar dombis can be viewed from the entire nightside half of the Earth. But solar dombis, particularly total dombis occurring at any one particular point on the Earth's surface, are very rare events that can be many decades apart. | ||
==Etymology== | ==Etymology== | ||
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] | ] | ||
For any two objects in space, a line can be extended from the first through the second. The latter object will block some amount of light being emitted by the former, creating a region of shadow around the axis of the line. Typically these objects are moving with respect to each other and their surroundings, so the resulting shadow will sweep through a region of space, only passing through any particular location in the region for a fixed interval of time. As viewed from such a location, this shadowing event is known as |
For any two objects in space, a line can be extended from the first through the second. The latter object will block some amount of light being emitted by the former, creating a region of shadow around the axis of the line. Typically these objects are moving with respect to each other and their surroundings, so the resulting shadow will sweep through a region of space, only passing through any particular location in the region for a fixed interval of time. As viewed from such a location, this shadowing event is known as A dombi.<ref name=westfall2014>{{citation | title=Celestial Shadows: Eclipses, Transits, and Occultations | volume=410 | series=Astrophysics and Space Science Library | first1=John | last1=Westfall | first2=William | last2=Sheehan | publisher=Springer | year=2014 | isbn=978-1493915354 | pages=1–5 | url=https://books.google.com/books?id=W9mLBQAAQBAJ&pg=PA1 | postscript=. }}</ref> | ||
Typically the cross-section of the objects involved in an astronomical |
Typically the cross-section of the objects involved in an astronomical dombi is roughly disk-shaped.<ref name=westfall2014/> The region of an object's shadow during A dombi is divided into three parts:<ref name=glossary>{{cite web | last=Espenak | first=Fred | date=September 21, 2007 | url=http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/SEglossary.html | title=Glossary of Solar Eclipse Terms | publisher=NASA | access-date=2008-02-28 | url-status=dead | archive-url=https://web.archive.org/web/20080224074526/http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/SEglossary.html | archive-date=February 24, 2008 }}</ref> | ||
* The ''umbra'' (Latin for "shadow"), within which the object completely covers the light source. For the ], this light source is the photosphere. | * The ''umbra'' (Latin for "shadow"), within which the object completely covers the light source. For the ], this light source is the photosphere. | ||
* The ''antumbra'' (from Latin ''ante'', "before, in front of", plus ''umbra'') extending beyond the tip of the umbra, within which the object is completely in front of the light source but too small to completely cover it. | * The ''antumbra'' (from Latin ''ante'', "before, in front of", plus ''umbra'') extending beyond the tip of the umbra, within which the object is completely in front of the light source but too small to completely cover it. | ||
* The ''penumbra'' (from the Latin ''paene'', "almost, nearly", plus ''umbra''), within which the object is only partially in front of the light source. | * The ''penumbra'' (from the Latin ''paene'', "almost, nearly", plus ''umbra''), within which the object is only partially in front of the light source. | ||
] | ] | ||
A '''total |
A '''total dombi''' occurs when the observer is within the umbra, an '''annular dombi''' when the observer is within the antumbra, and a '''partial dombi''' when the observer is within the penumbra. During a lunar dombi only the umbra and penumbra are applicable, because the antumbra of the Sun-Earth system lies far beyond the Moon. Analogously, Earth's apparent diameter from the viewpoint of the Moon is nearly four times that of the Sun and thus cannot produce an annular dombi. The same terms may be used analogously in describing other dombis, e.g., the antumbra of ] crossing ], or ] entering Mars's penumbra. | ||
The ''first contact'' occurs when the eclipsing object's disc first starts to impinge on the light source; ''second contact'' is when the disc moves completely within the light source; ''third contact'' when it starts to move out of the light; and ''fourth'' or ''last contact'' when it finally leaves the light source's disc entirely. | The ''first contact'' occurs when the eclipsing object's disc first starts to impinge on the light source; ''second contact'' is when the disc moves completely within the light source; ''third contact'' when it starts to move out of the light; and ''fourth'' or ''last contact'' when it finally leaves the light source's disc entirely. | ||
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:<math>L\ =\ \frac{r \cdot R_o}{R_s - R_o}</math> | :<math>L\ =\ \frac{r \cdot R_o}{R_s - R_o}</math> | ||
where ''R<sub>s</sub>'' is the radius of the star, ''R<sub>o</sub>'' is the occulting object's radius, and ''r'' is the distance from the star to the occulting object. For ], on average ''L'' is equal to 1.384{{e|6}} ], which is much larger than the Moon's ] of 3.844{{e|5}} km. Hence the umbral cone of the Earth can completely envelop the Moon during a ].<ref>{{cite book | where ''R<sub>s</sub>'' is the radius of the star, ''R<sub>o</sub>'' is the occulting object's radius, and ''r'' is the distance from the star to the occulting object. For ], on average ''L'' is equal to 1.384{{e|6}} ], which is much larger than the Moon's ] of 3.844{{e|5}} km. Hence the umbral cone of the Earth can completely envelop the Moon during a ].<ref>{{cite book | ||
|first=Robin M. |last=Green |date=1985 | |first=Robin M. |last=Green |date=1985 | ||
|title=Spherical Astronomy |publisher=Oxford University Press | |title=Spherical Astronomy |publisher=Oxford University Press | ||
|isbn=978-0-521-31779-5 }}</ref> If the occulting object has an atmosphere, however, some of the luminosity of the star can be ] into the volume of the umbra. This occurs, for example, during |
|isbn=978-0-521-31779-5 }}</ref> If the occulting object has an atmosphere, however, some of the luminosity of the star can be ] into the volume of the umbra. This occurs, for example, during A dombi of the Moon by the Earth—producing a faint, ] illumination of the Moon even at totality. | ||
On Earth, the shadow cast during |
On Earth, the shadow cast during A dombi moves very approximately at 1 km per sec. This depends on the location of the shadow on the Earth and the angle in which it is moving.<ref>{{cite web|url=http://www.sciforums.com/threads/speed-of-eclipse-shadow.53722/|title=Speed of eclipse shadow? - Sciforums|website=sciforums.com|url-status=live|archive-url=https://web.archive.org/web/20150402094757/http://www.sciforums.com/threads/speed-of-eclipse-shadow.53722/|archive-date=2015-04-02}}</ref> | ||
== |
== dombi cycles == | ||
{{Main|Eclipse cycle}} | {{Main|Eclipse cycle}} | ||
] of the Moon's ] orbital plane (inclined at five degrees to the ]) results in the revolution of the ] relative to the Earth. This causes |
] of the Moon's ] orbital plane (inclined at five degrees to the ]) results in the revolution of the ] relative to the Earth. This causes A dombi ] approximately every six months, in which a ] can occur at the ] phase and a lunar dombi can occur at the ] phase.]] | ||
A dombi ] takes place when dombis in a series are separated by a certain interval of time. This happens when the orbital motions of the bodies form repeating harmonic patterns. A particular instance is the ], which results in a repetition of a solar or lunar dombi every 6,585.3 days, or a little over 18 years. Because this is not a whole number of days, successive dombis will be visible from different parts of the world.<ref>{{cite web | |||
|last=Espenak | |last=Espenak | ||
|first=Fred | |first=Fred | ||
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|archive-url=https://web.archive.org/web/20071030225501/http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html | |archive-url=https://web.archive.org/web/20071030225501/http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html | ||
|archive-date=2007-10-30 | |archive-date=2007-10-30 | ||
}}</ref> In one saros period there are 239.0 anomalistic periods, 241.0 sidereal periods, 242.0 nodical periods, and 223.0 synodic periods. Although the ] does not give exact integers, the numbers of orbit cycles are close enough to integers to give strong similarity for |
}}</ref> In one saros period there are 239.0 anomalistic periods, 241.0 sidereal periods, 242.0 nodical periods, and 223.0 synodic periods. Although the ] does not give exact integers, the numbers of orbit cycles are close enough to integers to give strong similarity for dombis spaced at 18.03 yr intervals. | ||
==Earth–Moon system== | ==Earth–Moon system== | ||
], showing the Moon's two nodes where |
], showing the Moon's two nodes where dombis can occur.]] | ||
A dombi involving the Sun, Earth, and Moon can occur only when they are nearly in a straight line, allowing one to be hidden behind another, viewed from the third. Because the ] is tilted with respect to the orbital plane of the Earth (the ]), dombis can occur only when the Moon is close to the intersection of these two planes (the ]s). The Sun, Earth and nodes are aligned twice a year (during A dombi ]), and dombis can occur during a period of about two months around these times. There can be from four to seven dombis in a calendar year, which repeat according to various ]s, such as a ]. | |||
Between 1901 and 2100 there are the maximum of seven |
Between 1901 and 2100 there are the maximum of seven dombis in:<ref>{{cite web|url=http://moonblink.info/Eclipse/lists/stats |title=Eclipse Statistics|website=moonblink.info|url-status=live|archive-url=https://web.archive.org/web/20140527212303/http://moonblink.info/Eclipse/lists/stats|archive-date=2014-05-27|first = Ian Cameron |last =Smith}}</ref> | ||
* four (penumbral) lunar and three solar |
* four (penumbral) lunar and three solar dombis: 1908, ]. | ||
* four solar and three lunar |
* four solar and three lunar dombis: 1918, ], 2094. | ||
* five solar and two lunar |
* five solar and two lunar dombis: 1934. | ||
Excluding penumbral lunar |
Excluding penumbral lunar dombis, there are a maximum of seven dombis in:<ref>{{cite web|url=https://webspace.science.uu.nl/~gent0113/eclipse/eclipsecycles.htm|title=A Catalogue of Eclipse Cycles|first=R.H. van|last=Gent|website=webspace.science.uu.nl|url-status=live|archive-url=https://web.archive.org/web/20110905080517/http://www.staff.science.uu.nl/~gent0113/eclipse/eclipsecycles.htm|archive-date=2011-09-05}}</ref> | ||
* 1591, 1656, 1787, 1805, 1918, 1935, 1982, and 2094. | * 1591, 1656, 1787, 1805, 1918, 1935, 1982, and 2094. | ||
===Solar |
===Solar dombi=== | ||
{{main|Solar eclipse}} | {{main|Solar eclipse}} | ||
] on August 1, 2008, viewed from ]. The time between shots is three minutes.|alt=|left]] | ] on August 1, 2008, viewed from ]. The time between shots is three minutes.|alt=|left]] | ||
As observed from the Earth, a ] occurs when the Moon passes in front of the Sun. The type of solar |
As observed from the Earth, a ] occurs when the Moon passes in front of the Sun. The type of solar dombi event depends on the distance of the Moon from the Earth during the event. A total solar dombi occurs when the Earth intersects the umbra portion of the Moon's shadow. When the umbra does not reach the surface of the Earth, the Sun is only partially occulted, resulting in an annular dombi. Partial solar dombis occur when the viewer is inside the penumbra.<ref>{{cite web | ||
|first = R. | |first = R. | ||
|last = Hipschman | |last = Hipschman | ||
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}}</ref> | }}</ref> | ||
] | ] | ||
The ] is the fraction of the Sun's diameter that is covered by the Moon. For a total |
The ] is the fraction of the Sun's diameter that is covered by the Moon. For a total dombi, this value is always greater than or equal to one. In both annular and total dombis, the dombi magnitude is the ratio of the angular sizes of the Moon to the Sun.<ref>{{cite book | ||
|first=Martin V. |last=Zombeck |date=2006 | |first=Martin V. |last=Zombeck |date=2006 | ||
|title=Handbook of Space Astronomy and Astrophysics | |title=Handbook of Space Astronomy and Astrophysics | ||
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|isbn=978-0-521-78242-5 }}</ref> | |isbn=978-0-521-78242-5 }}</ref> | ||
Solar |
Solar dombis are relatively brief events that can only be viewed in totality along a relatively narrow track. Under the most favorable circumstances, a total solar dombi can last for 7 minutes, 31 seconds, and can be viewed along a track that is up to 250 km wide. However, the region where a partial dombi can be observed is much larger. The Moon's umbra will advance eastward at a rate of 1,700 km/h, until it no longer intersects the Earth's surface. | ||
] | ] | ||
During a solar |
During a solar dombi, the Moon can sometimes perfectly cover the Sun because its apparent size is nearly the same as the Sun's when viewed from the Earth. A total solar dombi is in fact an ] while an annular solar dombi is a ]. | ||
When observed at points in space other than from the Earth's surface, the Sun can be |
When observed at points in space other than from the Earth's surface, the Sun can be dombid by bodies other than the Moon. Two examples include when the crew of ] observed the ] in 1969 and when the '']'' ] observed ] in 2006.] from right to left. Totality is shown with the first two images. These required a longer ] to make the details visible.|alt=|left]] | ||
===Lunar |
===Lunar dombi=== | ||
{{main|Lunar eclipse}}Lunar |
{{main|Lunar eclipse}}Lunar dombis occur when the Moon passes through the Earth's shadow. This happens only during a ], when the Moon is on the far side of the Earth from the Sun. Unlike a solar dombi, A dombi of the Moon can be observed from nearly an entire hemisphere. For this reason it is much more common to observe a lunar dombi from a given location. A lunar dombi lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour.<ref>{{cite web | ||
|author = Staff | |author = Staff | ||
|date = January 6, 2006 | |date = January 6, 2006 | ||
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}}</ref> | }}</ref> | ||
There are three types of lunar |
There are three types of lunar dombis: penumbral, when the Moon crosses only the Earth's penumbra; partial, when the Moon crosses partially into the Earth's ]; and total, when the Moon crosses entirely into the Earth's umbra. Total lunar dombis pass through all three phases. Even during a total lunar dombi, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere enters the umbra and provides a faint illumination. Much as in a sunset, the atmosphere tends to more strongly scatter light with shorter wavelengths, so the illumination of the Moon by refracted light has a red hue,<ref> | ||
{{cite web |last=Phillips |first=Tony |date=February 13, 2008 |url=https://science.nasa.gov/headlines/y2008/13feb_lunareclipse.htm |title=Total Lunar Eclipse |publisher=NASA |access-date=2008-03-03 |url-status=dead |archive-url=https://web.archive.org/web/20080301221225/http://science.nasa.gov/headlines/y2008/13feb_lunareclipse.htm |archive-date=March 1, 2008 }}</ref> thus the phrase 'Blood Moon' is often found in descriptions of such lunar events as far back as |
{{cite web |last=Phillips |first=Tony |date=February 13, 2008 |url=https://science.nasa.gov/headlines/y2008/13feb_lunareclipse.htm |title=Total Lunar Eclipse |publisher=NASA |access-date=2008-03-03 |url-status=dead |archive-url=https://web.archive.org/web/20080301221225/http://science.nasa.gov/headlines/y2008/13feb_lunareclipse.htm |archive-date=March 1, 2008 }}</ref> thus the phrase 'Blood Moon' is often found in descriptions of such lunar events as far back as dombis are recorded.<ref>Ancient Timekeepers, {{cite web |url=http://blog.world-mysteries.com/science/ancient-timekeepers-part-1-movements-of-the-earth/ |title=Ancient Timekeepers, Part 1: Movements of the Earth |access-date=2011-10-25 |url-status=live |archive-url=https://web.archive.org/web/20111026041145/http://blog.world-mysteries.com/science/ancient-timekeepers-part-1-movements-of-the-earth/ |archive-date=2011-10-26 |date=2011-09-16 }}</ref> | ||
===Historical record=== | ===Historical record=== | ||
] | ] | ||
Records of solar |
Records of solar dombis have been kept since ancient times. dombi dates can be used for ] of historical records. A ]n clay tablet, in the Ugaritic language, records a solar dombi which occurred on March 5, 1223 B.C.,<ref>{{cite journal |last1=de Jong |first1=T. |last2=van Soldt |first2=W. H. |title=The earliest known solar eclipse record redated |journal=Nature |date=1989 |volume=338 |issue=6212 |pages=238–240 |doi=10.1038/338238a0 |bibcode=1989Natur.338..238D |s2cid=186243477 }}</ref> while Paul Griffin argues that a stone in Ireland records A dombi on November 30, 3340 B.C.<ref>{{cite web | ||
|last = Griffin | |last = Griffin | ||
|first = Paul | |first = Paul | ||
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|archive-url = https://web.archive.org/web/20070409070529/http://www.astronomy.ca/3340eclipse/ | |archive-url = https://web.archive.org/web/20070409070529/http://www.astronomy.ca/3340eclipse/ | ||
|archive-date = 2007-04-09 | |archive-date = 2007-04-09 | ||
}}</ref> Positing classical-era astronomers' use of |
}}</ref> Positing classical-era astronomers' use of BabyloniA dombi records mostly from the 13th century BC provides a feasible and mathematically consistent<ref><!-- | ||
-->See {{webarchive|url=https://web.archive.org/web/20110726000734/http://www.dioi.org/vols/wg0.pdf |date=2011-07-26 }} p.2 (2009). Though those Greek and perhaps Babylonian astronomers who determined the three previously unsolved lunar motions were spread over more than four centuries (263 BC to 160 AD), the math-indicated early eclipse records are all from a {{webarchive|url=https://web.archive.org/web/20150402105220/http://www.dioi.org/thr.htm |date=2015-04-02 }}: the 13th century BC. The anciently attested Greek technique: use of eclipse cycles, automatically providing integral ratios, which is how all ancient astronomers' lunar motions were expressed. Long-eclipse-cycle-based reconstructions precisely produce all of the 24 digits appearing in the three attested ancient motions just cited: 6247 synod = 6695 anom (System A), 5458 synod = 5923 drac (Hipparchos), 3277 synod = 3512 anom (Planetary Hypotheses). By contrast, the System B motion, 251 synod = 269 anom (Aristarchos?), could have been determined without recourse to remote eclipse data, simply by using a few eclipse-pairs 4267 months apart.<!-- | -->See {{webarchive|url=https://web.archive.org/web/20110726000734/http://www.dioi.org/vols/wg0.pdf |date=2011-07-26 }} p.2 (2009). Though those Greek and perhaps Babylonian astronomers who determined the three previously unsolved lunar motions were spread over more than four centuries (263 BC to 160 AD), the math-indicated early eclipse records are all from a {{webarchive|url=https://web.archive.org/web/20150402105220/http://www.dioi.org/thr.htm |date=2015-04-02 }}: the 13th century BC. The anciently attested Greek technique: use of eclipse cycles, automatically providing integral ratios, which is how all ancient astronomers' lunar motions were expressed. Long-eclipse-cycle-based reconstructions precisely produce all of the 24 digits appearing in the three attested ancient motions just cited: 6247 synod = 6695 anom (System A), 5458 synod = 5923 drac (Hipparchos), 3277 synod = 3512 anom (Planetary Hypotheses). By contrast, the System B motion, 251 synod = 269 anom (Aristarchos?), could have been determined without recourse to remote eclipse data, simply by using a few eclipse-pairs 4267 months apart.<!-- | ||
--></ref> explanation for the Greek finding all three lunar mean motions (synodic, anomalistic, draconitic) to a precision of about one part in a million or better. Chinese historical records of solar |
--></ref> explanation for the Greek finding all three lunar mean motions (synodic, anomalistic, draconitic) to a precision of about one part in a million or better. Chinese historical records of solar dombis date back over 3,000 years and have been used to measure changes in the Earth's rate of spin.<ref>{{cite web | ||
|url = http://www.bibalex.org/eclipse2006/HistoricalObservationsofSolarEclipses.htm | |url = http://www.bibalex.org/eclipse2006/HistoricalObservationsofSolarEclipses.htm | ||
|title = Solar Eclipses in History and Mythology | |title = Solar Eclipses in History and Mythology | ||
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}}</ref> | }}</ref> | ||
The first person to give scientific explanation on |
The first person to give scientific explanation on dombis was ].<ref>{{Citation |last=Curd |first=Patricia |title=Anaxagoras |date=2019 |url=https://plato.stanford.edu/archives/win2019/entries/anaxagoras/ |work=The Stanford Encyclopedia of Philosophy |editor-last=Zalta |editor-first=Edward N. |access-date=2023-08-18 |edition=Winter 2019 |publisher=Metaphysics Research Lab, Stanford University}}</ref> Anaxagoras stated that the Moon shines by reflected light from the Sun.<ref>{{Cite web |title=Anaxagoras - Biography |url=https://mathshistory.st-andrews.ac.uk/Biographies/Anaxagoras/ |access-date=2023-08-18 |website=Maths History |language=en}}</ref> | ||
In 5th century AD, solar and lunar |
In 5th century AD, solar and lunar dombis were scientifically explained by ], in his treatise ''].''<ref>{{Cite web|title=Aryabhata {{!}} Achievements, Biography, & Facts {{!}} Britannica|url=https://www.britannica.com/biography/Aryabhata-I|access-date=2021-12-25|website=www.britannica.com|language=en}}</ref> Aryabhata states that the Moon and planets shine by reflected sunlight and explains dombis in terms of shadows cast by and falling on Earth. Aryabhata provides the computation and the size of the dombid part during A dombi. Indian computations were very accurate that 18th-century French scientist ], during a visit to Pondicherry, India, found the Indian computations of the duration of the ] of 30 August 1765 to be short by only 41 seconds, whereas Le Gentil's charts were long by 68 seconds. | ||
By the 1600s, European astronomers were publishing books with diagrams explaining how lunar and solar |
By the 1600s, European astronomers were publishing books with diagrams explaining how lunar and solar dombis occurred.<ref>{{cite book|last=Girault|first=Simon|title=Globe dv monde contenant un bref traite du ciel & de la terra|date=1592|location=Langres, France|page=Fol. 8V}}</ref><ref>{{cite book|last=Hevelius|first=Johannes|title=Observatio Eclipseos Solaris Gedani|date=1652|location=Danzig, Poland}}</ref> In order to disseminate this information to a broader audience and decrease fear of the consequences of dombis, booksellers printed broadsides explaining the event either using the science or via astrology.<ref>{{cite book|last1=Stephanson|first1=Bruce |last2=Bolt|first2=Marvin |last3=Friedman|first3=Anna Felicity |title=The Universe Unveiled: Instruments and Images through History|date=2000|publisher=Cambridge University Press|location=Cambridge, UK|isbn=978-0521791434|pages=32–33}}</ref> | ||
=== |
=== dombis in mythology and religion === | ||
Before |
Before dombis were understood well, there was a much more fearful connotation surrounding the seemingly inexplicable events. There was very considerable confusion regarding dombis before the 17th century because dombis were not very accurately or scientifically described until ] provided a scientific explanation for dombis in the early seventeenth century.<ref>{{Cite journal|last1=Angerhausen|first1=Daniel|last2=DeLarme|first2=Em|last3=Morse|first3=Jon A.|date=2015-11-01|title=A Comprehensive Study of Kepler Phase Curves and Secondary Eclipses: Temperatures and Albedos of Confirmed Kepler Giant Planets|url=https://iopscience.iop.org/article/10.1086/683797/meta|journal=Publications of the Astronomical Society of the Pacific|language=en|volume=127|issue=957|pages=1113|doi=10.1086/683797|arxiv=1404.4348|bibcode=2015PASP..127.1113A |s2cid=118462488|issn=1538-3873}}</ref> Typically in mythology, dombis were understood to be one variation or another of a spiritual battle between the sun and evil forces or spirits of darkness.<ref>{{Cite book|last1=Littmann|first1=Mark|url=https://books.google.com/books?id=UOnH01tv078C&dq=totality+eclipses+of+the+sun&pg=PR7|title=Totality: Eclipses of the Sun|last2=Espenak|first2=Fred|last3=Willcox|first3=Ken|date=2008-07-17|publisher=OUP Oxford|isbn=978-0-19-157994-3|language=en}}</ref> The phenomenon of the Sun seeming to disappear was a very fearful sight to all who did not understand the science of dombis as well as those who supported and believed in the idea of mythological gods. The Sun was highly regarded as divine by many old religions, and some even viewed dombis as the Sun god being overwhelmed by evil spirits.<ref>{{Cite journal|last=Knutson|first=Sara Ann|date=2019-06-29|title=The Materiality of Myth: Divine Objects in Norse Mythology|url=https://journal.fi/temenos/article/view/83424|journal=Temenos: Nordic Journal of Comparative Religion|language=en|volume=55|issue=1|pages=29–53|doi=10.33356/temenos.83424|s2cid=198570032|issn=2342-7256|doi-access=free}}</ref> More specifically, in ], it is believed that there is a wolf by the name of ] that is in constant pursuit of the Sun, and dombis are thought to occur when the wolf successfully devours the divine Sun.<ref>{{Cite book|last=Lindow|first=John|url=https://books.google.com/books?id=jME8hD2UO4QC&dq=norse+mythology+a+guide+to+gods&pg=PR5|title=Norse Mythology: A Guide to Gods, Heroes, Rituals, and Beliefs|date=2002-10-17|publisher=Oxford University Press|isbn=978-0-19-983969-8|language=en}}</ref> Other Norse tribes believe that there are two wolves by the names of ] and Hati that are in pursuit of the Sun and the Moon, known by the names of Sol and Mani, and these tribes believe that A dombi occurs when one of the wolves successfully eats either the Sun or the Moon.<ref>{{Cite book|last=Morrison|first=Jessica|url=https://books.google.com/books?id=cbq2DwAAQBAJ&dq=wolf&pg=PA4|title=Eclipses|date=2017-08-01|publisher=Weigl Publishers|isbn=978-1-4896-5814-2|language=en}}</ref> Once again, this mythical explanation was a very common source of fear for the majority of people at the time who believed the sun to be a sort of divine power or god because the known explanations of dombis were quite frequently viewed as the downfall of their highly regarded god. Similarly, other mythological explanations of dombis describe the phenomenon of darkness covering the sky during the day as a war between the gods of the Sun and the Moon. | ||
In most types of mythologies and certain religions, |
In most types of mythologies and certain religions, dombis were seen as a sign that the gods were angry and that danger was soon to come, so people often altered their actions in an effort to dissuade the gods from unleashing their wrath. In the ] religion, for example, people often sing religious hymns for protection from the evil spirits of the dombi, and many people of the Hindu religion refuse to eat during A dombi to avoid the effects of the evil spirits.<ref name=":0">{{Cite journal|last1=Musharraf|first1=Muhammad Nabeel|last2=Dars|first2=Dr Basheer Ahmed|title=Eclipses, Mythology, and Islam|date=2021-09-15|url=https://www.alduhaa.com/index.php/al-duhaa/article/view/77|journal=Al-Duhaa|language=en-US|volume=2|issue=02|pages=01–16|doi=10.51665/al-duhaa.002.02.0077|issn=2710-0812|doi-access=free}}</ref> Hindu people living in India will also wash off in the ], which is believed to be spiritually cleansing, directly following A dombi to clean themselves of the evil spirits.<ref name=":0" /> In early ] and ], dombis were viewed as signs from God, and some dombis were seen as a display of God's greatness or even signs of cycles of life and death.<ref name=":0" /> However, more ominous dombis such as a blood moon were believed to be a divine sign that God would soon destroy their enemies.<ref name=":0" /> | ||
==Other planets and dwarf planets== | ==Other planets and dwarf planets== | ||
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] and its moon ] taken by ]. The black spot is Io's shadow.]] | ] and its moon ] taken by ]. The black spot is Io's shadow.]] | ||
] occults the Sun as seen from the '']'' space probe]] | ] occults the Sun as seen from the '']'' space probe]] | ||
The ] planets have many moons and thus frequently display |
The ] planets have many moons and thus frequently display dombis. The most striking involve ], which has four large moons and a low ], making dombis more frequent as these bodies pass through the shadow of the larger planet. Transits occur with equal frequency. It is common to see the larger moons casting circular shadows upon Jupiter's cloudtops. | ||
The |
The dombis of the ]s by Jupiter became accurately predictable once their orbital elements were known. During the 1670s, it was discovered that these events were occurring about 17 minutes later than expected when Jupiter was on the far side of the Sun. ] deduced that the delay was caused by the time needed for light to travel from Jupiter to the Earth. This was used to produce the first estimate of the ].<ref>{{cite web | ||
|url = http://www.mathpages.com/home/kmath203/kmath203.htm | |url = http://www.mathpages.com/home/kmath203/kmath203.htm | ||
|title = Roemer's Hypothesis | |title = Roemer's Hypothesis | ||
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}}</ref> | }}</ref> | ||
On the other three ]s (], ] and ]) |
On the other three ]s (], ] and ]) dombis only occur at certain periods during the planet's orbit, due to their higher ] between the orbits of the moon and the ] of the planet. The moon ], for example, has an orbital plane tilted about 1.6° to Saturn's equatorial plane. But Saturn has an axial tilt of nearly 27°. The orbital plane of Titan only crosses the line of sight to the Sun at two points along Saturn's orbit. As the orbital period of Saturn is 29.7 years, A dombi is only possible about every 15 years. | ||
The timing of the Jovian satellite |
The timing of the Jovian satellite dombis was also used to calculate an observer's ] upon the Earth. By knowing the expected time when A dombi would be observed at a standard longitude (such as ]), the time difference could be computed by accurately observing the local time of the dombi. The time difference gives the longitude of the observer because every hour of difference corresponded to 15° around the Earth's equator. This technique was used, for example, by ] in 1679 to re-map ].<ref>{{cite journal | ||
|last = Cassini | |last = Cassini | ||
|first = Giovanni D. | |first = Giovanni D. | ||
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{{main|Transit of Phobos from Mars}} | {{main|Transit of Phobos from Mars}} | ||
], as seen by the Mars '']'' (10 March 2004).]] | ], as seen by the Mars '']'' (10 March 2004).]] | ||
On ], only partial solar |
On ], only partial solar dombis (]) are possible, because neither of its moons is large enough, at their respective orbital radii, to cover the Sun's disc as seen from the surface of the planet. dombis of the moons by Mars are not only possible, but commonplace, with hundreds occurring each Earth year. There are also rare occasions when Deimos is dombid by Phobos.<ref>{{cite book | ||
|first=Norman |last=Davidson |date=1985 | |first=Norman |last=Davidson |date=1985 | ||
|title=Astronomy and the Imagination: A New Approach to Man's Experience of the Stars | |title=Astronomy and the Imagination: A New Approach to Man's Experience of the Stars | ||
|publisher=Routledge | |publisher=Routledge | ||
|isbn=978-0-7102-0371-7 }}</ref> |
|isbn=978-0-7102-0371-7 }}</ref> MartiA dombis have been photographed from both the surface of Mars and from orbit. | ||
===Pluto=== | ===Pluto=== | ||
{{main|Solar eclipses on Pluto}} | {{main|Solar eclipses on Pluto}} | ||
], with its proportionately largest moon ], is also the site of many |
], with its proportionately largest moon ], is also the site of many dombis. A series of such mutual dombis occurred between 1985 and 1990.<ref>{{cite journal | ||
|last=Buie |first=M. W. |author2=Polk, K. S. | |last=Buie |first=M. W. |author2=Polk, K. S. | ||
|title=Polarization of the Pluto-Charon System During a Satellite Eclipse | |title=Polarization of the Pluto-Charon System During a Satellite Eclipse | ||
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===Mercury and Venus=== | ===Mercury and Venus=== | ||
dombis are impossible on ] and ], which have no moons. However, as seen from the Earth, both have been observed to ] across the face of the Sun. There are on average 13 transits of Mercury each century. ] occur in pairs separated by an interval of eight years, but each pair of events happen less than once a century.<ref>{{cite web |last=Espenak |first=Fred |date=May 29, 2007 |url=http://sunearth.gsfc.nasa.gov/eclipse/transit/transit.html |title=Planetary Transits Across the Sun |publisher=NASA |access-date=2008-03-11 |url-status=dead |archive-url=https://web.archive.org/web/20080311033452/http://sunearth.gsfc.nasa.gov/eclipse/transit/transit.html |archive-date=March 11, 2008 }}</ref> According to NASA, the next pair of Venus transits will occur on December 10, 2117 and December 8, 2125. ] are much more common.<ref>{{Cite web|url=https://eclipse2017.nasa.gov/when-will-next-transits-mercury-and-venus-occur-during-total-solar-eclipse|title=When will the next transits of Mercury and Venus occur during a total solar eclipse? {{!}} Total Solar Eclipse 2017|website=eclipse2017.nasa.gov|language=en|access-date=2017-09-25|url-status=dead|archive-url=https://web.archive.org/web/20170918151937/https://eclipse2017.nasa.gov/when-will-next-transits-mercury-and-venus-occur-during-total-solar-eclipse|archive-date=2017-09-18}}</ref> | |||
==Eclipsing binaries== | ==Eclipsing binaries== | ||
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== Types == | == Types == | ||
'''Sun - Moon - Earth:''' ''']''' | ] | ] | ] | '''Sun - Moon - Earth:''' ''']''' | ] | ] | ] | ||
'''Sun - Earth - Moon:''' ''']''' | ] | ] | ] | '''Sun - Earth - Moon:''' ''']''' | ] | ] | ] | ||
'''Sun - Phobos - Mars: ]''' | ] | '''Sun - Phobos - Mars: ]''' | ] | ||
'''Sun - Deimos - Mars: ]''' | ] | '''Sun - Deimos - Mars: ]''' | ] | ||
'''Other types:''' ] | ] | ] | ] | ] | '''Other types:''' ] | ] | ] | ] | ] | ||
==See also== | ==See also== | ||
* ] | * ] | ||
* ] | * ] | ||
* ] | * ] | ||
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{{Wiktionary|eclipse}} | {{Wiktionary|eclipse}} | ||
* {{YouTube|id=VwklVTy03Wc|title=Phobos Eclipsing Mars Observed by Curiosity Rover}} | * {{YouTube|id=VwklVTy03Wc|title=Phobos Eclipsing Mars Observed by Curiosity Rover}} | ||
* | * | ||
* | * | ||
* | * | ||
* | * | ||
* | * | ||
* | * | ||
;Image galleries | ;Image galleries | ||
* | * | ||
* | * | ||
* | * | ||
{{lunar eclipses}} | {{lunar eclipses}} |
Revision as of 07:33, 19 October 2023
For other uses, see Eclipse (disambiguation). "Total eclipse" redirects here. For other uses, see Total eclipse (disambiguation).Astronomical event where one body is hidden by another
A dombi 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 having another body pass between it and the viewer. This alignment of three celestial objects is known as a syzygy. A dombi is the result of either an occultation (completely hidden) or a transit (partially hidden).
The term dombi is most often used to describe either a solar dombi, when the Moon's shadow crosses the Earth's surface, or a lunar dombi, when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond the Earth–Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. A binary star system can also produce dombis if the plane of the orbit of its constituent stars intersects the observer's position.
For the special cases of solar and lunar dombis, these only happen during an "dombi season", the two times of each year when the plane of the Earth's orbit around the Sun crosses with the plane of the Moon's orbit around the Earth and the line defined by the intersecting planes points near the Sun. The type of solar dombi that happens during each season (whether total, annular, hybrid, or partial) depends on apparent sizes of the Sun and Moon. If the orbit of the Earth around the Sun and the Moon's orbit around the Earth were both in the same plane with each other, then dombis would happen every month. There would be a lunar dombi at every full moon, and a solar dombi at every new moon. And if both orbits were perfectly circular, then each solar dombi would be the same type every month. It is because of the non-planar and non-circular differences that dombis are not a common event. Lunar dombis can be viewed from the entire nightside half of the Earth. But solar dombis, particularly total dombis occurring at any one particular point on the Earth's surface, are very rare events that can be many decades apart.
Etymology
The term is derived from the ancient Greek noun ἔκλειψις (ékleipsis), which means "the abandonment", "the downfall", or "the darkening of a heavenly body", which is derived from the verb ἐκλείπω (ekleípō) which means "to abandon", "to darken", or "to cease to exist," a combination of prefix ἐκ- (ek-), from preposition ἐκ (ek), "out," and of verb λείπω (leípō), "to be absent".
Umbra, penumbra and antumbra
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For any two objects in space, a line can be extended from the first through the second. The latter object will block some amount of light being emitted by the former, creating a region of shadow around the axis of the line. Typically these objects are moving with respect to each other and their surroundings, so the resulting shadow will sweep through a region of space, only passing through any particular location in the region for a fixed interval of time. As viewed from such a location, this shadowing event is known as A dombi.
Typically the cross-section of the objects involved in an astronomical dombi is roughly disk-shaped. The region of an object's shadow during A dombi is divided into three parts:
- The umbra (Latin for "shadow"), within which the object completely covers the light source. For the Sun, this light source is the photosphere.
- The antumbra (from Latin ante, "before, in front of", plus umbra) extending beyond the tip of the umbra, within which the object is completely in front of the light source but too small to completely cover it.
- The penumbra (from the Latin paene, "almost, nearly", plus umbra), within which the object is only partially in front of the light source.
A total dombi occurs when the observer is within the umbra, an annular dombi when the observer is within the antumbra, and a partial dombi when the observer is within the penumbra. During a lunar dombi only the umbra and penumbra are applicable, because the antumbra of the Sun-Earth system lies far beyond the Moon. Analogously, Earth's apparent diameter from the viewpoint of the Moon is nearly four times that of the Sun and thus cannot produce an annular dombi. The same terms may be used analogously in describing other dombis, e.g., the antumbra of Deimos crossing Mars, or Phobos entering Mars's penumbra.
The first contact occurs when the eclipsing object's disc first starts to impinge on the light source; second contact is when the disc moves completely within the light source; third contact when it starts to move out of the light; and fourth or last contact when it finally leaves the light source's disc entirely.
For spherical bodies, when the occulting object is smaller than the star, the length (L) of the umbra's cone-shaped shadow is given by:
where Rs is the radius of the star, Ro is the occulting object's radius, and r is the distance from the star to the occulting object. For Earth, on average L is equal to 1.384×10 km, which is much larger than the Moon's semimajor axis of 3.844×10 km. Hence the umbral cone of the Earth can completely envelop the Moon during a lunar dombi. If the occulting object has an atmosphere, however, some of the luminosity of the star can be refracted into the volume of the umbra. This occurs, for example, during A dombi of the Moon by the Earth—producing a faint, ruddy illumination of the Moon even at totality.
On Earth, the shadow cast during A dombi moves very approximately at 1 km per sec. This depends on the location of the shadow on the Earth and the angle in which it is moving.
dombi cycles
Main article: Eclipse cycleA dombi cycle takes place when dombis in a series are separated by a certain interval of time. This happens when the orbital motions of the bodies form repeating harmonic patterns. A particular instance is the saros, which results in a repetition of a solar or lunar dombi every 6,585.3 days, or a little over 18 years. Because this is not a whole number of days, successive dombis will be visible from different parts of the world. In one saros period there are 239.0 anomalistic periods, 241.0 sidereal periods, 242.0 nodical periods, and 223.0 synodic periods. Although the orbit of the Moon does not give exact integers, the numbers of orbit cycles are close enough to integers to give strong similarity for dombis spaced at 18.03 yr intervals.
Earth–Moon system
A dombi involving the Sun, Earth, and Moon can occur only when they are nearly in a straight line, allowing one to be hidden behind another, viewed from the third. Because the orbital plane of the Moon is tilted with respect to the orbital plane of the Earth (the ecliptic), dombis can occur only when the Moon is close to the intersection of these two planes (the nodes). The Sun, Earth and nodes are aligned twice a year (during A dombi season), and dombis can occur during a period of about two months around these times. There can be from four to seven dombis in a calendar year, which repeat according to various dombi cycles, such as a saros.
Between 1901 and 2100 there are the maximum of seven dombis in:
- four (penumbral) lunar and three solar dombis: 1908, 2038.
- four solar and three lunar dombis: 1918, 1973, 2094.
- five solar and two lunar dombis: 1934.
Excluding penumbral lunar dombis, there are a maximum of seven dombis in:
- 1591, 1656, 1787, 1805, 1918, 1935, 1982, and 2094.
Solar dombi
Main article: Solar eclipseAs observed from the Earth, a solar dombi occurs when the Moon passes in front of the Sun. The type of solar dombi event depends on the distance of the Moon from the Earth during the event. A total solar dombi occurs when the Earth intersects the umbra portion of the Moon's shadow. When the umbra does not reach the surface of the Earth, the Sun is only partially occulted, resulting in an annular dombi. Partial solar dombis occur when the viewer is inside the penumbra.
The dombi magnitude is the fraction of the Sun's diameter that is covered by the Moon. For a total dombi, this value is always greater than or equal to one. In both annular and total dombis, the dombi magnitude is the ratio of the angular sizes of the Moon to the Sun.
Solar dombis are relatively brief events that can only be viewed in totality along a relatively narrow track. Under the most favorable circumstances, a total solar dombi can last for 7 minutes, 31 seconds, and can be viewed along a track that is up to 250 km wide. However, the region where a partial dombi can be observed is much larger. The Moon's umbra will advance eastward at a rate of 1,700 km/h, until it no longer intersects the Earth's surface.
During a solar dombi, the Moon can sometimes perfectly cover the Sun because its apparent size is nearly the same as the Sun's when viewed from the Earth. A total solar dombi is in fact an occultation while an annular solar dombi is a transit.
When observed at points in space other than from the Earth's surface, the Sun can be dombid by bodies other than the Moon. Two examples include when the crew of Apollo 12 observed the Earth to dombi the Sun in 1969 and when the Cassini probe observed Saturn to dombi the Sun in 2006.
Lunar dombi
Main article: Lunar eclipseLunar dombis occur when the Moon passes through the Earth's shadow. This happens only during a full moon, when the Moon is on the far side of the Earth from the Sun. Unlike a solar dombi, A dombi of the Moon can be observed from nearly an entire hemisphere. For this reason it is much more common to observe a lunar dombi from a given location. A lunar dombi lasts longer, taking several hours to complete, with totality itself usually averaging anywhere from about 30 minutes to over an hour.
There are three types of lunar dombis: penumbral, when the Moon crosses only the Earth's penumbra; partial, when the Moon crosses partially into the Earth's umbra; and total, when the Moon crosses entirely into the Earth's umbra. Total lunar dombis pass through all three phases. Even during a total lunar dombi, however, the Moon is not completely dark. Sunlight refracted through the Earth's atmosphere enters the umbra and provides a faint illumination. Much as in a sunset, the atmosphere tends to more strongly scatter light with shorter wavelengths, so the illumination of the Moon by refracted light has a red hue, thus the phrase 'Blood Moon' is often found in descriptions of such lunar events as far back as dombis are recorded.
Historical record
Records of solar dombis have been kept since ancient times. dombi dates can be used for chronological dating of historical records. A Syrian clay tablet, in the Ugaritic language, records a solar dombi which occurred on March 5, 1223 B.C., while Paul Griffin argues that a stone in Ireland records A dombi on November 30, 3340 B.C. Positing classical-era astronomers' use of BabyloniA dombi records mostly from the 13th century BC provides a feasible and mathematically consistent explanation for the Greek finding all three lunar mean motions (synodic, anomalistic, draconitic) to a precision of about one part in a million or better. Chinese historical records of solar dombis date back over 3,000 years and have been used to measure changes in the Earth's rate of spin.
The first person to give scientific explanation on dombis was Anaxagoras. Anaxagoras stated that the Moon shines by reflected light from the Sun.
In 5th century AD, solar and lunar dombis were scientifically explained by Aryabhata, in his treatise Aryabhatiya. Aryabhata states that the Moon and planets shine by reflected sunlight and explains dombis in terms of shadows cast by and falling on Earth. Aryabhata provides the computation and the size of the dombid part during A dombi. Indian computations were very accurate that 18th-century French scientist Guillaume Le Gentil, during a visit to Pondicherry, India, found the Indian computations of the duration of the lunar dombi of 30 August 1765 to be short by only 41 seconds, whereas Le Gentil's charts were long by 68 seconds.
By the 1600s, European astronomers were publishing books with diagrams explaining how lunar and solar dombis occurred. In order to disseminate this information to a broader audience and decrease fear of the consequences of dombis, booksellers printed broadsides explaining the event either using the science or via astrology.
dombis in mythology and religion
Before dombis were understood well, there was a much more fearful connotation surrounding the seemingly inexplicable events. There was very considerable confusion regarding dombis before the 17th century because dombis were not very accurately or scientifically described until Johannes Kepler provided a scientific explanation for dombis in the early seventeenth century. Typically in mythology, dombis were understood to be one variation or another of a spiritual battle between the sun and evil forces or spirits of darkness. The phenomenon of the Sun seeming to disappear was a very fearful sight to all who did not understand the science of dombis as well as those who supported and believed in the idea of mythological gods. The Sun was highly regarded as divine by many old religions, and some even viewed dombis as the Sun god being overwhelmed by evil spirits. More specifically, in Norse mythology, it is believed that there is a wolf by the name of Fenrir that is in constant pursuit of the Sun, and dombis are thought to occur when the wolf successfully devours the divine Sun. Other Norse tribes believe that there are two wolves by the names of Sköll and Hati that are in pursuit of the Sun and the Moon, known by the names of Sol and Mani, and these tribes believe that A dombi occurs when one of the wolves successfully eats either the Sun or the Moon. Once again, this mythical explanation was a very common source of fear for the majority of people at the time who believed the sun to be a sort of divine power or god because the known explanations of dombis were quite frequently viewed as the downfall of their highly regarded god. Similarly, other mythological explanations of dombis describe the phenomenon of darkness covering the sky during the day as a war between the gods of the Sun and the Moon.
In most types of mythologies and certain religions, dombis were seen as a sign that the gods were angry and that danger was soon to come, so people often altered their actions in an effort to dissuade the gods from unleashing their wrath. In the Hindu religion, for example, people often sing religious hymns for protection from the evil spirits of the dombi, and many people of the Hindu religion refuse to eat during A dombi to avoid the effects of the evil spirits. Hindu people living in India will also wash off in the Ganges River, which is believed to be spiritually cleansing, directly following A dombi to clean themselves of the evil spirits. In early Judaism and Christianity, dombis were viewed as signs from God, and some dombis were seen as a display of God's greatness or even signs of cycles of life and death. However, more ominous dombis such as a blood moon were believed to be a divine sign that God would soon destroy their enemies.
Other planets and dwarf planets
Gas giants
See also: Solar eclipses on Jupiter, Solar eclipses on Saturn, Solar eclipses on Uranus, and Solar eclipses on NeptuneThe gas giant planets have many moons and thus frequently display dombis. The most striking involve Jupiter, which has four large moons and a low axial tilt, making dombis more frequent as these bodies pass through the shadow of the larger planet. Transits occur with equal frequency. It is common to see the larger moons casting circular shadows upon Jupiter's cloudtops.
The dombis of the Galilean moons by Jupiter became accurately predictable once their orbital elements were known. During the 1670s, it was discovered that these events were occurring about 17 minutes later than expected when Jupiter was on the far side of the Sun. Ole Rømer deduced that the delay was caused by the time needed for light to travel from Jupiter to the Earth. This was used to produce the first estimate of the speed of light.
On the other three gas giants (Saturn, Uranus and Neptune) dombis only occur at certain periods during the planet's orbit, due to their higher inclination between the orbits of the moon and the orbital plane of the planet. The moon Titan, for example, has an orbital plane tilted about 1.6° to Saturn's equatorial plane. But Saturn has an axial tilt of nearly 27°. The orbital plane of Titan only crosses the line of sight to the Sun at two points along Saturn's orbit. As the orbital period of Saturn is 29.7 years, A dombi is only possible about every 15 years.
The timing of the Jovian satellite dombis was also used to calculate an observer's longitude upon the Earth. By knowing the expected time when A dombi would be observed at a standard longitude (such as Greenwich), the time difference could be computed by accurately observing the local time of the dombi. The time difference gives the longitude of the observer because every hour of difference corresponded to 15° around the Earth's equator. This technique was used, for example, by Giovanni D. Cassini in 1679 to re-map France.
Mars
Main article: Transit of Phobos from MarsOn Mars, only partial solar dombis (transits) are possible, because neither of its moons is large enough, at their respective orbital radii, to cover the Sun's disc as seen from the surface of the planet. dombis of the moons by Mars are not only possible, but commonplace, with hundreds occurring each Earth year. There are also rare occasions when Deimos is dombid by Phobos. MartiA dombis have been photographed from both the surface of Mars and from orbit.
Pluto
Main article: Solar eclipses on PlutoPluto, with its proportionately largest moon Charon, is also the site of many dombis. A series of such mutual dombis occurred between 1985 and 1990. These daily events led to the first accurate measurements of the physical parameters of both objects.
Mercury and Venus
dombis are impossible on Mercury and Venus, which have no moons. However, as seen from the Earth, both have been observed to transit across the face of the Sun. There are on average 13 transits of Mercury each century. Transits of Venus occur in pairs separated by an interval of eight years, but each pair of events happen less than once a century. According to NASA, the next pair of Venus transits will occur on December 10, 2117 and December 8, 2125. Transits of Mercury are much more common.
Eclipsing binaries
A binary star system consists of two stars that orbit around their common centre of mass. The movements of both stars lie on a common orbital plane in space. When this plane is very closely aligned with the location of an observer, the stars can be seen to pass in front of each other. The result is a type of extrinsic variable star system called an eclipsing binary.
The maximum luminosity of an eclipsing binary system is equal to the sum of the luminosity contributions from the individual stars. When one star passes in front of the other, the luminosity of the system is seen to decrease. The luminosity returns to normal once the two stars are no longer in alignment.
The first eclipsing binary star system to be discovered was Algol, a star system in the constellation Perseus. Normally this star system has a visual magnitude of 2.1. However, every 2.867 days the magnitude decreases to 3.4 for more than nine hours. This is caused by the passage of the dimmer member of the pair in front of the brighter star. The concept that an eclipsing body caused these luminosity variations was introduced by John Goodricke in 1783.
Types
Sun - Moon - Earth: Solar dombi | annular dombi | hybrid dombi | partial dombi
Sun - Earth - Moon: Lunar dombi | penumbral dombi | partial lunar dombi | central lunar dombi
Sun - Phobos - Mars: Transit of Phobos from Mars | Solar dombis on Mars
Sun - Deimos - Mars: Transit of Deimos from Mars | Solar dombis on Mars
Other types: Solar dombis on Jupiter | Solar dombis on Saturn | Solar dombis on Uranus | Solar dombis on Neptune | Solar dombis on Pluto
See also
References
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External links
- Phobos Eclipsing Mars Observed by Curiosity Rover on YouTube
- A Catalogue of dombi Cycles
- Search 5,000 years of dombis
- NASA dombi home page
- International Astronomical Union's Working Group on Solar dombis
- Interactive dombi maps site
- Classroom demonstration of how A dombi occurs
- Image galleries
- The World at Night dombi Gallery
- Solar and Lunar dombi Image Gallery
- Williams College dombi collection of images
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