Occultation

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Occultation

In Shia Islam the Occultation
The Occultation

The Occultation in Shi'a Islam refers to a belief that the messianic figure, Mahdi, who in Shi'a thought is an ismah male descendant of the founder of Islam, Muhammad, has been born but has disappeared and will one day return and fill the world with justice....
is a term used to designate the hidden state of the Imam of the Time
Imamah (Shi'a doctrine)

Imamah is the Shia Islam doctrine of religious, spiritual and political Islamic leadership of the Ummah. The Shi?ah believe that the A'immah are the true Caliphs or Succession to Muhammad of Muhammad, and Twelver Shi`ism and Ismaili Shi?ah further that Imams are possessed of supernatural knowledge, authority, and Ismah as well as being par...
. See also occult (disambiguation)
Occult (disambiguation)

Occult refers to secret or hidden knowledge, usually of a mystical nature.Occult may also refer to* Occultists, occult practitioners: List of occultists...
.

An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer.

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Encyclopedia

An occultation is an event that occurs when one object is hidden by another object that passes between it and the observer. The word is used in astronomy

Astronomy

Astronomy is the science of Astronomical object and Phenomenon that originate outside the Earth's atmosphere . It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the physical cosmology....
(see below) and can also be used in a general (non-astronomical) sense to describe when an object in the foreground occult

Occult

The word occult comes from the Latin word occultus , referring to "knowledge of the hidden". In the medical sense it is used to refer to a structure or process that is hidden, e.g....
s (covers up) objects in the background. In the general sense, occultation applies to the visual scene from low-flying aircraft and in Computer-Generated Imagery

Computer-generated imagery

Computer-generated imagery is the application of the field of computer graphics or, more specifically, 3D computer graphics to special effects in films, television programs, Television commercials, simulators and simulation generally, and printed media....
(CGI) technology, where foreground objects obscure distant ones in a dynamic way as the scene changes.

Astronomical events. These include transit

Astronomical transit

File:Moon transit of sun large.oggThe term transit or astronomical transit has three meanings in astronomy:* A transit is the astronomy event that occurs when one celestial body appears to move across the face of another celestial body, as seen by an observer at some particular vantage point....
s and eclipse

Eclipse

Astronomical transit

Mercury (planet)

Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 88 days. The orbit of Mercury has the highest Orbital eccentricity of all the Solar System planets, and it has the smallest axial tilt....
or Venus

Venus

Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus , the Roman mythology goddess of love....
across the Sun

Sun

The Sun , a G V star, is the star at the center of the Solar System. The Earth and other matter orbit the Sun, which by itself accounts for about 98.6% of the Solar System's mass....
's disk. The word eclipse

Eclipse

Syzygy

In broadest terms, Syzygy is a kind of unity, especially through coordination or alignment, most commonly used in the astronomical and/or astrological sense....
.

Occultations and eclipses

Every time an occultation occurs, an eclipse

Eclipse

An eclipse is an astronomical event that occurs when one celestial object moves into the shadow of another. The term is derived from the ancient Greek noun , from verb , "I cease to exist," a combination of prefix , from preposition , "out," and of verb , "I am absent"....
also occurs. Consider a so-called "eclipse" of the Sun by the Moon, as seen from Earth. In this event, the Moon physically moves between Earth and the Sun, thus blocking out a portion or all of the bright disk of the Sun. Although this phenomenon is usually referred to as an "eclipse", this term is a misnomer, because the Moon is not eclipsing the Sun; instead the Moon is occulting the Sun. When the Moon occults the Sun, it casts a small shadow on the surface of the Earth, and therefore the Moon's shadow is partially eclipsing Earth. So a so-called "solar eclipse" actually consists of (i) an occultation of the Sun by the Moon, as seen from Earth, and (ii) a partial eclipse
Eclipse

An eclipse is an astronomical event that occurs when one celestial object moves into the shadow of another. The term is derived from the ancient Greek noun , from verb , "I cease to exist," a combination of prefix , from preposition , "out," and of verb , "I am absent"....
of Earth by the Moon's shadow.

By contrast, an "eclipse" of the Moon is in fact a true eclipse: the Moon moves into the shadow cast back into space by Earth, and is said to be eclipsed by Earth's shadow. As seen from the surface of the Moon, Earth passes directly between the Moon and the Sun, thus blocking or occulting the Sun as seen by a hypothetical lunar observer. Again, every eclipse also entails an occultation.

Occultations by the Moon

The term occultation is most frequently used to describe those relatively frequent occasions when the Moon

Moon

The Moon is Earth's only natural satellite and the List of natural satellites by diameter satellite in the Solar System. The average centre-to-centre distance from the Earth to the Moon is km, about thirty times the diameter of the Earth....
passes in front of a star

Star

A star is a massive, luminous ball of Plasma that is held together by its own gravity. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth....
during the course of its orbital motion around the Earth. Since the Moon has no atmosphere and stars have no appreciable angular size, a star that is occulted by the moon will disappear or reappear very nearly instantaneously on the moon's edge, or limb. Events that take place on the Moon's dark limb are of particular interest to observers, because the lack of glare allows these occultations to more easily be observed and timed.

The Moon's orbit is inclined to the ecliptic

Ecliptic

The ecliptic is the apparent path that the Sun traces out in the sky during the year. As it appears to move in the sky in relation to the stars, the apparent path aligns with the planets throughout the course of the year....
(see orbit of the Moon), and any stars with an ecliptic latitude of less than about 6.5 degrees may be occulted by it. There are three first magnitude stars that are sufficiently close to the ecliptic that they may be occulted by the Moon and by planets -- Regulus

Regulus

Regulus is the brightest star in the constellation Leo and list of brightest stars in the nighttime sky, and lies approximately 77.5 light years from Earth....
, Spica

Spica

Spica is the brightest star in the constellation Virgo , and the list of brightest stars in the nighttime sky. It is 260 light years distant from Earth....
and Antares

Antares

Antares is a red supergiant star in the Milky Way galaxy and list of brightest stars in the nighttime sky . Along with Aldebaran, Spica, and Regulus it is one of the four brightest stars near the ecliptic....
. Occultations of Aldebaran

Aldebaran

Aldebaran is the brightest star in the constellation Taurus and list of brightest stars in the nighttime sky. Because of its location in the head of Taurus, it has historically been called the Bull's Eye....
are presently only possible by the Moon, because the planets pass Aldebaran to the north. Neither planetary nor lunar occultations of Pollux

Pollux (star)

Pollux, also cataloged as Beta Geminorum , is an orange giant star approximately 34 light-years away in the constellation of Gemini ....
are currently possible. However, in the far future, occultations of Aldebaran and Pollux will be possible, as they were in the far past. Some deep-sky objects, such as the Pleiades, can also be occulted by the moon.

Within a few kilometres of the edge of an occultation's predicted path, referred to as its northern or southern limit, an observer may see the star intermittently disappearing and reappearing as the irregular limb of the Moon moves past the star, creating what is known as a Grazing lunar occultation

Grazing lunar occultation

A lunar occultation occurs when the Moon, moving along its orbital path, passes in front of a star or other celestial object, as seen by an observer ....
. From an observational and scientific standpoint, these "grazes" are the most dynamic and interesting of lunar occultations.

The accurate timing of lunar occultations is performed regularly by (primarily amateur) astronomers. Lunar occultations timed to an accuracy of a few tenths of a second have various scientific uses, particularly in refining our knowledge of lunar topography. Photoelectric analysis of lunar occultations have also discovered some stars to be very close visual or spectroscopic binaries

Binary star

A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star or secondary....
. Early radio astronomers found occultations of radio sources by the Moon valuable for determining their exact positions, because the long wavelength of radio waves limited the resolution available through direct observation.

Several times during the year, someone on Earth can usually observe the Moon occulting a planet. Since planets, unlike stars, have significant angular sizes, lunar occultations of planets will create a narrow zone on earth from which a partial occultation of the planet will occur. An observer located within that narrow zone could observe the planet's disk partly blocked by the slowly moving moon.

Occultation by planets

Stars may also be occulted by planets. In 1959, Venus

Venus

Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus , the Roman mythology goddess of love....
occulted Regulus

Regulus

Regulus is the brightest star in the constellation Leo and list of brightest stars in the nighttime sky, and lies approximately 77.5 light years from Earth....
. Uranus

Uranus

Uranus is the seventh planet from the Sun and the third-largest and fourth most massive planet in the Solar System. It is named after the ancient Greek deity of the sky Uranus the father of Kronos and grandfather of Zeus ....
' rings were first discovered when that planet occulted a star in 1977. On the evening of July 2-July 3, 1989, Saturn

Saturn

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn, along with Jupiter, Uranus and Neptune, is classified as a gas giant....
passed in front of the 5th magnitude star 28 Sagittarii

Sagittarius (constellation)

Sagittarius is one of the constellations of the zodiac. Its name is Latin for the archer, and its symbol is , a stylized arrow. Sagittarius is commonly represented as a centaur drawing a bow....
. Pluto, which was re-designated as a "dwarf planet" in 2006, occulted stars in 1988, 2002, and 2006, allowing its tenuous atmosphere to be studied.

It is also possible for one planet to occult another planet. However, these mutual occultations of planets are extremely rare. The last such event occurred on January 3, 1818 and will next occur on November 22, 2065, in both cases involving the same two planets -- Venus and Jupiter. Technically speaking, when the foreground planet is smaller in apparent size than the background planet, the event should be called a "mutual planetary transit." When the foreground planet is larger in apparent size than the background planet, the event should be called a "mutual planetary occultation." (See Transit

Astronomical transit

Twice during the orbital cycles of Jupiter and Saturn, the equatorial (and satellite) planes of those planets are aligned with earth's orbital plane, resulting in a series of mutual occultations and eclipses between the moons of these giant planets. These orbital alignments have also occurred artificially when unmanned spacecraft have traversed these planetary systems, resulting in photographs such as the one shown here. The terms "eclipse," "occultation" and "transit" are also used to describe these events. A satellite of Jupiter (for example) may be eclipsed (i.e. made dimmer because it moves into Jupiter's shadow), occulted (i.e. hidden from view because Jupiter lies on our line of sight), or may transit (i.e. pass in front of) Jupiter's disk.

Double occultations

It is possible that the moon or another celestial body can occult multiple celestial bodies at the same time. Such events are extremely rare and can be seen only from a small part of the world. The last event of such type was on April 23rd, 1998 when the moon occulted Venus and Jupiter simultaneously for observers on Ascension Island

Ascension Island

Ascension Island is an isolated island of volcanic origin in the South Atlantic Ocean, around from the coast of Africa, and from the coast of South America....
.

Occulting satellites

The Big Occulting Steerable Satellite (BOSS) was a proposed satellite

Satellite

In the context of spaceflight, a satellite is an Physical body which has been placed into orbit by human endeavor. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
that would work in conjunction with a telescope

Telescope

A telescope is an instrument designed for the observation of remote objects by the collection of electromagnetic radiation. The first known practically functioning telescopes were invented in the Netherlands at the beginning of the 17th century....
to detect planet

Planet

A planet , as 2006 definition of planet by the International Astronomical Union , is a celestial body orbiting a star or Stellar evolution#Stellar remnants that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared the neighbourhood of planetesimals....
s around distant stars. The satellite consists of a large, very lightweight sheet, and a set of maneuvering thrusters and navigation systems. It would maneuver to a position along the line of sight between the telescope and a nearby star. The satellite would thereby block the radiation from the star, permitting the orbiting planets to be observed.

The proposed satellite would have a dimension of 70 m × 70 m, a mass of about 600 kg, and maneuver by means of an ion drive engine in combination with using the sheet as a light sail. Positioned at a distance of 100,000 km from the telescope, it would block more than 99.998% of the starlight.

There are two possible configurations of this satellite. The first would work with a space telescope, most likely positioned near the Earth

Earth

Earth is the third planet from the Sun. Earth is the largest of the terrestrial planets in the Solar System in diameter, mass and density. It is also referred to as the World and Wiktionary:Terra.Note that by International Astronomical Union convention, the term "Terra" is used for naming extensive land masses, rather...
's L2 Lagrangian point

Lagrangian point

The Lagrangian points , are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects ....
. The second would place the satellite in a highly elliptical orbit about the Earth, and work in conjunction with a ground telescope. At the apogee of the orbit, the satellite would remain relatively stationary with respect to the ground, allowing longer exposure times.

An updated version of this design is called the Starshade, which uses a sunflower

Sunflower

The sunflower is an annual plant in the family Asteraceae and native to the Americas, with a large flowering head . The stem can grow as high as 3 meters , and the flower head can reach 30 cm in diameter with the "large" seeds....
-shaped coronagraph

Coronagraph

A coronagraph is a Telescope attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved....
disc. A comparable proposal was also made for a satellite to occult bright X-ray sources, called an X-ray Occulting Steerable Satellite or XOSS.

Occultations and transits between 1800 and 2100

This table lists occultations and transits of bright stars and planets by solar planets.

Day	Time (UT)	Foreground planet	Background object	Elongation
December 9, 1802	07:36	Mercury Mercury (planet) Mercury is the innermost and smallest planet in the Solar System, orbiting the Sun once every 88 days. The orbit of Mercury has the highest Orbital eccentricity of all the Solar System planets, and it has the smallest axial tilt....	Acrab	16,2° West
December 9, 1808	20:34	Mercury	Saturn Saturn Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn, along with Jupiter, Uranus and Neptune, is classified as a gas giant....	20,3° West
December 22, 1810	06:32	Venus Venus Venus is the second-closest planet to the Sun, orbiting it every 224.7 Earth days. The planet is named after Venus , the Roman mythology goddess of love....	Xi-2 Sagittarii	11,1° East
January 3, 1818	21:52	Venus	Jupiter Jupiter Jupiter is the fifth planet from the Sun and the Solar system by size planet within the Solar System. It is two and a half times as massive as all of the other planets in our Solar System combined....	16,5° West
July 11, 1825	09:10	Venus	Delta-1 Tauri	44,4° West
July 11, 1837	12:50	Mercury	Eta Geminorum Eta Geminorum Eta Geminorum is a triple star system in the constellation Gemini . It also has the traditional names Tejat Prior, Propus and Praepes....	17,8° West
May 9, 1841	19:35	Venus	17 Tauri	9,2° East
September 27, 1843	18:00	Venus	Eta Virginis Eta Virginis Eta Virginis is a star in the constellation Virgo . It also has the traditional name Zaniah.Zaniah is about 204 light years distant from the Sun, and has apparent magnitude +3.9 and is of stellar classification A2IV....	3,2° West
December 16, 1850	11:28	Mercury	Lambda Sagittarii Lambda Sagittarii Lambda Sagittarii is a star within the constellation Sagittarius . The star marks the top of the Archer's bow, whence its traditional name Kaus Borealis....	10,2° East
May 22, 1855	05:04	Venus	Epsilon Geminorum Epsilon Geminorum Epsilon Geminorum is a star in the constellation of Gemini . It also has traditional name Mebsuta .It is located on the outstretched right "leg" of the twin Castor ....	37,4° East
June 30, 1857	00:25	Saturn Saturn Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn, along with Jupiter, Uranus and Neptune, is classified as a gas giant....	Delta Geminorum Delta Geminorum Delta Geminorum is a star in the constellation Gemini . It also has the traditional name Wasat.The traditional name comes from the Arabic language word for "middle", but it is not certain whether this refers to the middle of Gemini or of the nearby constellation Orion ....	8,4° East
December 5, 1865	14:20	Mercury	Lambda Sagittarii	21,0° East
February 28, 1876	05:13	Jupiter Jupiter Jupiter is the fifth planet from the Sun and the Solar system by size planet within the Solar System. It is two and a half times as massive as all of the other planets in our Solar System combined....	Acrab	97,6° West
June 7, 1881	20:54	Mercury	Epsilon Geminorum	21,2° East
December 9, 1906	17:40	Venus	Acrab	14,9° West
July 27, 1910	02:53	Venus	Eta Geminorum	31,0° West
December 16, 1937	18:38	Mercury	Omicron Sagittarii	11,6° East
June 10, 1940	02:21	Mercury	Epsilon Geminorum	20,1° East
October 25, 1947	01:45	Venus	Zuben-el-genubi Alpha Librae Alpha Librae is the second brightest star in the constellation Libra . It also has the traditional name Zubenelgenubi. The name, from Arabic language ????? ??????? , means "southern claw" and was coined before Libra was recognized as distinct from Scorpius....	13,5° East
July 7, 1959	14:30	Venus	Regulus Regulus Regulus is the brightest star in the constellation Leo and list of brightest stars in the nighttime sky, and lies approximately 77.5 light years from Earth....	44,5° East
September 27, 1965	15:30	Mercury	Eta Virginis Eta Virginis Eta Virginis is a star in the constellation Virgo . It also has the traditional name Zaniah.Zaniah is about 204 light years distant from the Sun, and has apparent magnitude +3.9 and is of stellar classification A2IV....	2.6° West
May 13, 1971	20:00	Jupiter	Beta Scorpii (both components)	169,5° West
April 8, 1976	01:00	Mars MARS In cryptography, MARS is a block cipher that was IBM's submission to the Advanced Encryption Standard process. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm....	Epsilon Geminorum	81,3° East
November 17, 1981	14:27	Venus	Nunki	47,0° East
November 19, 1984	01:32	Venus	Lambda Sagittarii	39,2° East
December 4, 2015	16.14	Mercury	Theta Ophiuchi	9,6° East
February 17, 2035	15:19	Venus	Pi Sagittarii Pi Sagittarii Pi Sagittarii is a triple star system in the constellation Sagittarius . It also has the traditional name Albaldah. It is known as ?? in Chinese....	42,1° West
October 1, 2044	22:00	Venus	Regulus	38,9° West
February 23, 2046	19:24	Venus	Rho-1 Sagittarii	45,4° West
November 10, 2052	07:20	Mercury	Zuben-el-genubi	2,8° West
November 22, 2065	12:45	Venus	Jupiter	7,9° West
July 15, 2067	11:56	Mercury	Neptune NEPTUNE =Overview=The project, along with sister project, VENUS, offers a unique approach to ocean science. Traditionally, ocean scientists have relied on infrequent ship cruises or space-based satellites to carry out their research....	18,4° West
August 10, 2069	20.25	Venus	Zavijava	38,4° East
October 3, 2078	22:00	Mars	Theta Ophiuchi	71,4° East
August 11, 2079	01:30	Mercury	Mars MARS In cryptography, MARS is a block cipher that was IBM's submission to the Advanced Encryption Standard process. MARS was selected as an AES finalist in August 1999, after the AES2 conference in March 1999, where it was voted as the fifth and last finalist algorithm....	11,3° West
October 27, 2088	13:43	Mercury	Jupiter	4,7° West
April 7, 2094	10:48	Mercury	Jupiter	1,8° West

These events are not visible everywhere the occulting body and the occulted body are above the skyline. Some events are barely visible, because they take place in close proximity to the Sun.

Mutual planetary transits and occultations

In rare cases, one planet can transit in front of another. The next time this will happen (as seen from Earth) will be on November 22 2065 at about 12:43 UTC

Coordinated Universal Time

Coordinated Universal Time is a time standard based on International Atomic Time with leap seconds added at irregular intervals to compensate for the Earth's slowing rotation....
, when Venus near superior conjunction (with an angular diameter

Angular diameter

Jupiter

Jupiter is the fifth planet from the Sun and the Solar system by size planet within the Solar System. It is two and a half times as massive as all of the other planets in our Solar System combined....
(with an angular diameter of 30.9"); however, this will take place only 8° west of the Sun, and will therefore not be visible to the unaided/unprotected eye. When the nearer object has a larger angular diameter

Angular diameter

The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle. In the vision sciences it is called the visual angle....
than the farther object, thus covering it completely, the event is not a transit but an occultation. Before transiting Jupiter, Venus will occult Jupiter's moon

Natural satellite

A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called the primary. Technically, the term natural satellite could refer to a planet orbiting a star, or a dwarf galaxy orbiting a major galaxy, but it is normally synonymous with moon and used to identify non-artificial satellites...
Ganymede

Ganymede (moon)

'Ganymede' is a Moons of Jupiter and the List of natural satellites by diameter in the Solar System. Completing an orbit in a little more than seven days, it is the seventh satellite and third Galilean satellite from Jupiter....
at around 11:24 UTC as seen from some southernmost parts of Earth. Parallax

Parallax

Parallax is an apparent displacement or difference of orientation of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines....
will cause actual observed times to vary by a few minutes, depending on the precise location of the observer.

There are only 18 mutual planetary transits and occultations as seen from Earth between 1700 and 2200. Note the long break of events between 1818 and 2065.

19 September 1702 - Jupiter occults Neptune
20 July 1705 - Mercury transits Jupiter
14 July 1708 - Mercury occults Uranus

4 October 1708 - Mercury transits Jupiter
28 May 1737 - Venus occults Mercury
29 August 1771 - Venus transits Saturn
21 July 1793 - Mercury occults Uranus
9 December 1808 - Mercury transits Saturn
3 January 1818 - Venus transits Jupiter
22 November 2065 - Venus transits Jupiter
15 July 2067 - Mercury occults Neptune
11 August 2079 - Mercury occults Mars
27 October 2088 - Mercury transits Jupiter
7 April 2094 - Mercury transits Jupiter
21 August 2104 - Venus occults Neptune
14 September 2123 - Venus transits Jupiter
29 July 2126 - Mercury occults Mars
3 December 2133 - Venus occults Mercury

The 1737 event was observed by John Bevis

John Bevis

John Bevis was an English Physician and astronomer. He is best known for discovering the Crab Nebula in 1731. Bevis has also observed an occultation by Venus of Mercury on May 28, 1737, and observed and found a prediction rule for eclipses of Jupiter's moons....
at Greenwich Observatory - it is the only detailed account of a mutual planetary occultation. A transit of Mars across Jupiter on 12 Sep 1170 was observed by the monk Gervase at Canterbury

Canterbury

Canterbury lies at the heart of the City of Canterbury, a local government district of Kent, in South East England. It lies on the River Stour....
, and by Chinese astronomers. In addition, an occultation of Mars by Venus was observed by M. Möstlin

Michael Maestlin

Michael Maestlin was a Germany astronomer and mathematician, known for being the mentor of Johannes Kepler....
at Heidelberg

Heidelberg

Heidelberg is a city in Baden-W?rttemberg, Germany. As of 2006, over 140,000 people live within the city's area. The town of Heidelberg is an administrative district of its own....
on October 3 1590.

External links

SPACE.com: (Sara Goudarzi) 15 August 2006 06:13 am ET

External references

Meeus, Jean: Astronomical Tables of the Sun, Moon and Planets. Richmond, Virginia: Willmann-Bell, Inc., 1995, ISBN 0-943396-45-X.

Marco Peuschel , Astronomische Tabellen für den Mond von 2007 bis 2016,Mondphasen, Apsiden, Knotendurchgänge, Maximale und minimale Deklinationswerte und Sternbedeckungen sowie ausführliche Ephemeriden für jeden Tag des Jahres , inkl. Mondauf-und Untergänge und physische Daten.