In twelver Shi'ism the occultation is the name given to the disappearance of the Twelfth Imam. See also Shi'a Islam Twelver Shi'ism ( ar اثنا عشرية Ithnāˤashariyyah) is the largest branch of Shi'a branch of Islam According to Twelver Shi'as Imam Hujjat al-Mahdī ( ar المهدى) (or Hujjat ibn Hasan ibn Ali is the twelfth Imam and the See also occult (disambiguation).

In this July, 1997 still frame captured from video, the bright star Aldebaran has just reappeared on the dark limb of the waning crescent moon in this predawn occultation.

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 (see below) and can also be used in a general (non-astronomical) sense to describe when an object in the foreground occults (covers up) objects in the background. Astronomy (from the Greek words astron (ἄστρον "star" and nomos (νόμος "law" is the scientific study The word occult comes from the Latin word occultus (clandestine hidden secret referring to "knowledge of the hidden" In the general sense, occultation applies to the visual scene from low-flying aircraft and in Computer-Generated Imagery (CGI) technology, where foreground objects obscure distant ones in a dynamic way as the scene changes. Computer animation Computer-generated imagery (also known as CGI) is the application of the field of Computer graphics or more specifically 3D computer graphics

Astronomical events. These include transits and eclipses. The term transit or astronomical transit has three meanings in astronomy A transit is the astronomical event that occurs when one An eclipse is an astronomical event that occurs when one Celestial object moves into the shadow of another The word transit refers to cases where the nearer object appears smaller in apparent size than the more distant object, such as transit of Mercury or Venus across the Sun's disk. The term transit or astronomical transit has three meanings in astronomy A transit is the astronomical event that occurs when one The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University The Sun (Sol is the Star at the center of the Solar System. The word eclipse generally refers to those instances in which one object moves into the shadow of another. An eclipse is an astronomical event that occurs when one Celestial object moves into the shadow of another Each of these three events is the visible effect of a syzygy. In broadest terms Syzygy (ˈsɪzɪʤi is a kind of unity especially through coordination or alignment most commonly used in the Astronomical and/or Astrological

Every time an occultation occurs, an eclipse also occurs. An eclipse is an astronomical event that occurs when one Celestial object moves into the shadow of another 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 of Earth by the Moon's shadow. An eclipse is an astronomical event that occurs when one Celestial object moves into the shadow of another

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

Occultation of a star by the Moon

The term occultation is most frequently used to describe those relatively frequent occasions when the Moon passes in front of a star during the course of its orbital motion around the Earth. A star is a massive luminous ball of plasma. The nearest star to Earth is the Sun, which is the source of most of the Energy on 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 (see orbit of the Moon), and any stars with an ecliptic latitude of less than about 6. The ecliptic is the apparent path that the Sun traces out in the sky during the year The orbit of the Moon around the Earth is completed in approximately 27 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, Spica and Antares. Regulus (α Leo / α Leonis / Alpha Leonis is the brightest star in the Constellation Leo and one of the brightest stars in the nighttime sky Spica (ˈspaɪkə (also known as α Vir / α Virginis / Alpha Virginis is the brightest star in the Constellation Virgo, and the 15th brightest star Antares (α Scorpii / Alpha Scorpii is a Red supergiant Star in the Milky Way Galaxy and the sixteenth brightest star Occultations of Aldebaran are presently only possible by the Moon, because the planets pass Aldebaran to the north. Aldebaran ( α Tau α Tauri Alpha Tauri is the brightest star in the constellation Taurus and one of the brightest stars in the nighttime sky Neither planetary nor lunar occultations of Pollux are currently possible. Pollux, also cataloged as Beta Geminorum (β Gem / β Geminorum is an Orange giant Star approximately 34 Light-years away in the Constellation However, in the far future, occultations of Aldebaran and Pollux will be possible, as they were in the far past.

Jupiter (the bright object in the upper right) a few minutes before being occulted by the Moon on June 7, 2005

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. 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 (normally on the 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. A binary star is a Star system consisting of two Stars orbiting around their Center of mass. 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.

On the 20th of January 2007, an occultation of Venus by the Moon was seen on the southern tip of Africa.

On 3rd of February 2007, an occultation of Saturn by the Moon was seen.

Occultation by planets

Stars may also be occulted by planets. In 1959, Venus occulted Regulus. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University Regulus (α Leo / α Leonis / Alpha Leonis is the brightest star in the Constellation Leo and one of the brightest stars in the nighttime sky Uranus' rings were first discovered when that planet occulted a star in 1977. On the evening of July 2-July 3, 1989, Saturn passed in front of the 5th magnitude star 28 Sagittarii. Events 310 - Pope Miltiades is elected 626 - In fear of assassination Li Shimin ambushes and kills his rival Events 324 - Battle of Adrianople Constantine I defeats Licinius, who flees to Byzantium. Year 1989 ( MCMLXXXIX) was a Common year starting on Sunday (link displays 1989 Gregorian calendar) 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. Events 1431 - Joan of Arc is handed over to the Bishop Pierre Cauchon. Year 1818 ( MDCCCXVIII) was a Common year starting on Thursday (link will display the full calendar of the Gregorian Calendar (or a Common Events 498 - Kofi Aseidu- After the death of Anastasius II, Symmachus is elected Pope in the Lateran Notable predictions and known events 2061 Expected expiration of the Singapore-Malaysia Water Agreement. 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 for a list of past and future events). The term transit or astronomical transit has three meanings in astronomy A transit is the astronomical event that occurs when one

A grazing occultation of Rhea, a moon of Saturn, by another moon, Dione

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. TemplateInfobox Planet.--> Rhea (ˈriːə, or as in Greek TemplateInfobox Planet.--> Dione (daɪˈoʊni, or as in Greek 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 is an island in the South Atlantic Ocean, around from the coast of Africa

Occulting satellites

The Big Occulting Steerable Satellite (BOSS) was a proposed satellite that would work in conjunction with a telescope to detect planets around distant stars. This article is about artificial satellites For natural satellites also known as moons see Natural satellite. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is 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. ^[1]

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. An ion thruster is a form of Electric propulsion used for Spacecraft propulsion that creates thrust by accelerating Ions Ion thrusters are characterized 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's L2 Lagrangian point. A space observatory is any instrument in Outer space which is used for observation of distant planets galaxies and other outer space objects EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 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. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from

An updated version of this design is called the Starshade, which uses a sunflower-shaped coronagraph disc. The New Worlds Mission is a project funded by NASA Institute for Advanced Concepts (NIAC headed by Dr The sunflower ( Helianthus annuus) is an Annual plant in the family Asteraceae and native to the Americas, with a large flowering A coronagraph is a telescopic attachment designed specifically to block out the harsh direct light from a Star, so that nearby objects can be resolved without burning A comparable proposal was also made for a satellite to occult bright X-ray sources, called an X-ray Occulting Steerable Satellite or XOSS. ^[2]

Occultations and transits between 1800 and 2100

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

These events are not visible everywhere the occulting body and the occulted body are above the skyline. Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's Notable predictions and known events 2070 February - An Active SETI message called Teen Age Message sent from the 70-meter Eupatoria Events 2492 BC - Traditional date of the defeat of Bel by Hayk, progenitor and founder of the Armenian nation Notable predictions and known events 2070 February - An Active SETI message called Teen Age Message sent from the 70-meter Eupatoria Events 312 - Constantine the Great is said to have received his famous Vision of the Cross. Notable predictions and known events 2082 All Classified information held by the British Government about the Falklands War Events 529 - First draft of Corpus Juris Civilis (a fundamental work in Jurisprudence) is issued by Eastern Roman Emperor The 2090s is a Decade that will start in the year 2090 and end in the year 2099. 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, when Venus near superior conjunction (with an angular diameter of 10. Events 498 - Kofi Aseidu- After the death of Anastasius II, Symmachus is elected Pope in the Lateran Notable predictions and known events 2061 Expected expiration of the Singapore-Malaysia Water Agreement. Conjunction is a term used in Positional astronomy and Astrology. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 6") will transit in front of Jupiter (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 than the farther object, thus covering it completely, the event is not a transit but an occultation. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle Before transiting Jupiter, Venus will occult Jupiter's moon Ganymede at around 11:24 UTC as seen from some southernmost parts of Earth. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. TemplateInfobox Planet.--> Ganymede (ˈgænɨmiːd, or as Greek Parallax will cause actual observed times to vary by a few minutes, depending on the precise location of the observer. 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

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

A simulation of Venus transiting Jupiter, as it did on January 3, 1818. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University

• 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 at Greenwich Observatory - it is the only detailed account of a mutual planetary occultation. Year 1737 ( MDCCXXXVII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a John Bevis ( October 31[[ 693]] or November 10[[ 695]] &ndash November 6, 1771) was an English doctor and Astronomer The Royal Observatory Greenwich (formerly the Royal Greenwich Observatory or RGO) was commissioned in 1675 by King Charles II, with the A transit of Mars across Jupiter on 12 Sep 1170 was observed by the monk Gervase at Canterbury, and by Chinese astronomers. Events 1213 - Albigensian Crusade: Simon de Montfort 5th Earl of Leicester, defeats Peter II of Aragon at the Canterbury ( ˈkæntəbɹ̩i is a City in eastern Kent in the South East region of England. In addition, an occultation of Mars by Venus was observed by M. Möstlin at Heidelberg on October 3, 1590. Michael Maestlin (also Mästlin Möstlin or Moestlin ( 30 September 1550 in Göppingen, Germany - 20 October 1631) was a Heidelberg is a city in Baden-Württemberg, Germany. As of 2006 over 140000 people live within the city's area Events 42 BC - First Battle of Philippi: Triumvirs Mark Antony and Octavian fight an indecisive battle with Caesar's

See also

• Asteroid occultation
• Transit (also for occultations of planets by other planets)
• Transit of Mercury
• Transit of Venus
• Solar eclipse
• Grazing lunar occultation
• Grazing occultation
• Syzygy
• Radio occultation

References

1. ^ C. An asteroid occultation occurs when an Asteroid passes in front of a Star ( occults a star temporarily blocking its light (as seen from The term transit or astronomical transit has three meanings in astronomy A transit is the astronomical event that occurs when one Transit of Mercury Closeup - Nov 8 2006jpg|right|thumb|300px|Close-up of Mercury during the Nov A transit of Venus across the Sun takes place when the Planet Venus passes directly between the Sun and Earth, obscuring a small portion of the A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured 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 (normally on the An Occultation is an astronomical event that occurs when one celestial object is hidden by another celestial object that passes between it and the observer In broadest terms Syzygy (ˈsɪzɪʤi is a kind of unity especially through coordination or alignment most commonly used in the Astronomical and/or Astrological Radio occultation (RO is a Remote sensing technique used for measuring the physical properties of a planetary Atmosphere. J. Copi, G. D. Starkman (2000). "The Big Occulting Steerable Satellite (BOSS)". The Astrophysical Journal 532: 581-592. doi:10.1086/308525. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.  
2. ^ The X-ray Occulting Steerable Satellite (XOSS). CASE. Retrieved on 2007-02-09. Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Events 474 - Zeno crowned as co-emperor of the Byzantine Empire.

External links

• International Occultation Timing Association (IOTA)
• Occultations of Regulus by planets (in German)
• Occultations of stars by planets (in German)
• Occultations of planets by other planets
• Big Occulting Steerable Satellite
• Moon, planets, asteroid occultations
• Mutual occultations (and conjunctions) of planets
• Society for Popular Astronomy - Occultation Section
• SPACE. com: Discovery Hints at a Quadrillion Space Rocks Beyond Neptune (Sara Goudarzi) 15 August 2006 06:13 am ET
• Scientists Use Novel Technique To Watch Occultations By Planets

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 [1], 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.