Ephemeris
Encyclopedia
An ephemeris is a table
of values
that gives the positions of astronomical objects in the sky
at a given time
or times. Different kinds of ephemerides are used for astronomy
and astrology
. Even though this was also one of the first applications of mechanical computers
, an ephemeris will still often be a simple printed table.
The position is given to astronomers in a spherical polar coordinate system of right ascension
and declination
or to astrologer
s in longitude
along the zodiac
al ecliptic
, and sometimes declination
. Astrological positions may be given for either noon
or midnight
.
An astronomical ephemeris may also provide data on astronomical phenomena of interest to astrologers and astronomers such as eclipse
s, Apparent retrograde motion/planetary stations, planetary
ingresses, sidereal time
, positions for the mean and true nodes of the moon
, the phases of the Moon, and sometimes even the position(s) of Chiron
, and other minor celestial bodies.
Astrologers also use other ephemerides that include tables of imaginary celestial bodies, such as Lilith, a term they use variously for the apogee of the Moon or the second focus of the Moon's orbit. Some ephemerides also contain a monthly aspectarian, while others often include the declination
of the planets as well as their longitudes, right ascension
s, or Cartesian coordinates.
s or comet
s at virtually any time desired by the user. Often there is an option to find the velocities of the bodies of interest, as well.
Typically, such ephemerides cover several centuries, past and future; the future ones can be covered because celestial mechanics
is an accurate theory. Nevertheless, there are secular phenomena
which cannot adequately be considered by ephemerides. The biggest uncertainties on planetary positions are due to the perturbations of numerous asteroids, most of whose masses and orbits are poorly known, rendering their effect uncertain. Reflecting the continuing influx of new data and observations, the JPL has to revise its published ephemerides at intervals of 20 years.
Solar system
ephemerides are essential for the navigation of spacecraft
and for all kinds of space observations of the planets, their natural satellite
s, star
s and galaxies.
Scientific ephemerides for sky observers mostly contain the position of the mentioned celestial body in right ascension
and declination
, because these coordinates are the most often used on star maps and telescopes. The equinox
of the coordinate system must be given. It is in nearly all cases either the actual equinox (the equinox valid for that moment, often referred to as "of date" or "current"), or that of one of the "standard" equinoxes, typically J2000.0, B1950.0, or J1900. Star maps are almost always in one of the standard equinoxes.
Scientific ephemerides often contain further useful data about the moon, planet, asteroid, or comet beyond the pure coordinates in the sky, such as elongation to the sun, brightness, distance, velocity, apparent diameter in the sky, phase angle, times of rise, transit, and set, etc.
Ephemerides of the planet Saturn
also sometimes contain the apparent inclination of its ring.
An ephemeris is usually only correct for a particular location on the Earth. In many cases the differences are too small to matter, but for nearby asteroids or the Moon
they can be quite important.
Global Positioning System
(GPS) navigation satellites transmit electronic ephemeris data consisting of health and exact location data that GPS receivers then use (together with the signal's elapsed travel time to the receiver) to calculate their own location on Earth using trilateration
.
Other modern ephemerides recently created are the EPM due to the Russian Institute for Applied Astronomy of the Russian Academy of Sciences, and the INPOP ones by the French IMCCE.
position along the ecliptic (the equinox being the center of Earth's rotational plane and Earth's orbital plane around the Sun). They use exactly the same referential frame of the astronomers, except for astrologers who study sidereal astrology
(Indian Astrology) and use a different ephemerids, based on the constellations.
Though astrology
is and always has been geocentric, heliocentric astrology
is an emerging field; for this purpose a standard ephemeris cannot be utilized, and because of this specialized heliocentric ephemerides must be calculated and used instead of the default geocentric ephemerides that are used in standard Western astrology
to construct the astrological chart/natal chart
.
Astrology links
Table (information)
A table is a means of arranging data in rows and columns.Production % of goalNorth 4087102%South 4093110% The use of tables is pervasive throughout all communication, research and data analysis. Tables appear in print media, handwritten notes, computer software, architectural...
of values
Quantity
Quantity is a property that can exist as a magnitude or multitude. Quantities can be compared in terms of "more" or "less" or "equal", or by assigning a numerical value in terms of a unit of measurement. Quantity is among the basic classes of things along with quality, substance, change, and relation...
that gives the positions of astronomical objects in the sky
Sky
The sky is the part of the atmosphere or outer space visible from the surface of any astronomical object. It is difficult to define precisely for several reasons. During daylight, the sky of Earth has the appearance of a pale blue surface because the air scatters the sunlight. The sky is sometimes...
at a given time
Time
Time is a part of the measuring system used to sequence events, to compare the durations of events and the intervals between them, and to quantify rates of change such as the motions of objects....
or times. Different kinds of ephemerides are used for astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...
and astrology
Astrology
Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...
. Even though this was also one of the first applications of mechanical computers
History of computing
The history of computing is longer than the history of computing hardware and modern computing technology and includes the history of methods intended for pen and paper or for chalk and slate, with or without the aid of tables...
, an ephemeris will still often be a simple printed table.
The position is given to astronomers in a spherical polar coordinate system of right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
or to astrologer
Astrologer
An astrologer practices one or more forms of astrology. Typically an astrologer draws a horoscope for the time of an event, such as a person's birth, and interprets celestial points and their placements at the time of the event to better understand someone, determine the auspiciousness of an...
s in longitude
Longitude
Longitude is a geographic coordinate that specifies the east-west position of a point on the Earth's surface. It is an angular measurement, usually expressed in degrees, minutes and seconds, and denoted by the Greek letter lambda ....
along the zodiac
Zodiac
In astronomy, the zodiac is a circle of twelve 30° divisions of celestial longitude which are centred upon the ecliptic: the apparent path of the Sun across the celestial sphere over the course of the year...
al ecliptic
Ecliptic
The ecliptic is the plane of the earth's orbit around the sun. In more accurate terms, it is the intersection of the celestial sphere with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun...
, and sometimes declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
. Astrological positions may be given for either noon
Noon
Noon is usually defined as 12 o'clock in the daytime. The word noon is also used informally to mean midday regarding the location of the sun not the middle of a persons day. Although this is a time around the middle of the day when people in many countries take a lunch break...
or midnight
Midnight
Midnight is the transition time period from one day to the next: the moment when the date changes. In the Roman time system, midnight was halfway between sunset and sunrise, varying according to the seasons....
.
An astronomical ephemeris may also provide data on astronomical phenomena of interest to astrologers and astronomers such as eclipse
Eclipse
An eclipse is an astronomical event that occurs when an astronomical object is temporarily obscured, either by passing into the shadow of another body or by having another body pass between it and the viewer...
s, Apparent retrograde motion/planetary stations, planetary
Planetary
Planetary means relating to a planet or planets. It can also refer to:* Planetary , a comic book series by Warren Ellis and John Cassaday* Planetary habitability, the measure of an astronomical body's potential to develop and sustain life...
ingresses, sidereal time
Sidereal time
Sidereal time is a time-keeping system astronomers use to keep track of the direction to point their telescopes to view a given star in the night sky...
, positions for the mean and true nodes of the moon
Lunar node
The lunar nodes are the orbital nodes of the Moon, that is, the points where the orbit of the Moon crosses the ecliptic . The ascending node is where the moon crosses to the north of the ecliptic...
, the phases of the Moon, and sometimes even the position(s) of Chiron
2060 Chiron
2060 Chiron is a minor planet in the outer Solar System. Discovered in 1977 by Charles T. Kowal , it was the first-known member of a new class of objects now known as centaurs, with an orbit between Saturn and Uranus.Although it was initially classified as an asteroid, it was later found to...
, and other minor celestial bodies.
Astrologers also use other ephemerides that include tables of imaginary celestial bodies, such as Lilith, a term they use variously for the apogee of the Moon or the second focus of the Moon's orbit. Some ephemerides also contain a monthly aspectarian, while others often include the declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
of the planets as well as their longitudes, right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
s, or Cartesian coordinates.
History
- 2nd millennium BCE — Ephemerides in Babylonian astronomy.
- 2nd millennium BCE — Panchanga tables based on JyotishaJyotishaHindu astrology , also Jyotish or Jyotisha, from Sanskrit , from "light, heavenly body") is the ancient Indian system of astronomy and astrology...
in the Vedic periodVedic periodThe Vedic period was a period in history during which the Vedas, the oldest scriptures of Hinduism, were composed. The time span of the period is uncertain. Philological and linguistic evidence indicates that the Rigveda, the oldest of the Vedas, was composed roughly between 1700–1100 BCE, also...
of Indian astronomy. - 2nd century CE - the Handy Tables of PtolemyPtolemyClaudius Ptolemy , was a Roman citizen of Egypt who wrote in Greek. He was a mathematician, astronomer, geographer, astrologer, and poet of a single epigram in the Greek Anthology. He lived in Egypt under Roman rule, and is believed to have been born in the town of Ptolemais Hermiou in the...
- 12th century CE — the Tables of ToledoTables of ToledoThe Toledan Tables, or Tables of Toledo, were astronomical tables which were used to predict the movements of the Sun, Moon and planets relative to the fixed stars...
, based largely on Arabic ZijZijZīj is the generic name applied to Islamic astronomical books that tabulate parameters used for astronomical calculations of the positions of the Sun, Moon, stars, and planets. The name is derived from the Middle Persian term zih or zīg, meaning cord...
sources of Islamic astronomy, were edited by Gerard of CremonaGerard of CremonaGerard of Cremona was an Italian translator of Arabic scientific works found in the abandoned Arab libraries of Toledo, Spain....
to form the standard European ephemeris until the Alfonsine tables. - 13th century — the Zij-i IlkhaniZij-i IlkhaniZīj-i Īlkhānī or Ilkhanic Tables is a Zij book with astronomical tables of planetary movements. It was compiled by the Persian astronomer Nasir al-Din al-Tusi in collaboration with his research team of astronomers at the Maragha observatory...
, or Ilkhanic Tables, were compiled at the Maragheh observatoryMaragheh observatoryMaragheh observatory is an astronomical observatory which was established in 1259 CE by Nasir al-Din al-Tusi, an Iranian scientist and astronomer...
in Persia. - 13th century — the Alfonsine tablesAlfonsine tablesThe Alfonsine tables provided data for computing the position of the Sun, Moon and planets relative to the fixed stars....
were compiled in Spain to correct anomalies in the Tables of Toledo, remaining the standard European ephemeris until the Prutenic Tables almost 300 years later. - 1408 — ChineseChinese astronomyAstronomy in China has a very long history, with historians considering that "they [the Chinese] were the most persistent and accurate observers of celestial phenomena anywhere in the world before the Arabs."...
Ephemeris Table [copy in Pepysian Library, Cambridge, UK (refer book '1434'); Chinese tables believed known to Regiomontanus]. - 1504 — While shipwrecked on the island of Jamaica, Christopher ColumbusChristopher ColumbusChristopher Columbus was an explorer, colonizer, and navigator, born in the Republic of Genoa, in northwestern Italy. Under the auspices of the Catholic Monarchs of Spain, he completed four voyages across the Atlantic Ocean that led to general European awareness of the American continents in the...
successfully predicted a lunar eclipse for the natives, using the Ephemeris of the German astronomer RegiomontanusRegiomontanusJohannes Müller von Königsberg , today best known by his Latin toponym Regiomontanus, was a German mathematician, astronomer, astrologer, translator and instrument maker....
. - 1551 — the Prutenic TablesPrutenic TablesThe Prutenic Tables , were an ephemeris by the astronomer Erasmus Reinhold published in 1551. They are sometimes called the Prussian Tables after Albert I, Duke of Prussia, who supported Reinhold and financed the printing...
of Erasmus ReinholdErasmus ReinholdErasmus Reinhold was a German astronomer and mathematician, considered to be the most influential astronomical pedagogue of his generation. He was born and died in Saalfeld, Saxony....
were published, based on Copernicus's theories. - 1554 — Johannes StadiusJohannes StadiusJohannes Stadius or Estadius was a Flemish astronomer, astrologer, and mathematician.-Life:...
published a well-known work known as Ephemerides novae at auctae that attempted to give accurate planetary positions. The effort was not entirely successful, and there were, for example, periodic errors in Stadius’ Mercury positions of up to ten degrees. - 1627 — the Rudolphine TablesRudolphine TablesThe Rudolphine Tables consist of a star catalogue and planetary tables published by Johannes Kepler in 1627 using data from Tycho Brahe's observations.-Previous tables:...
of Johannes KeplerJohannes KeplerJohannes Kepler was a German mathematician, astronomer and astrologer. A key figure in the 17th century scientific revolution, he is best known for his eponymous laws of planetary motion, codified by later astronomers, based on his works Astronomia nova, Harmonices Mundi, and Epitome of Copernican...
became the new standard.
Scientific ephemeris
For scientific uses, a modern planetary ephemeris comprises software that generates positions of the planets and often of their satellites, or of asteroidAsteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
s or comet
Comet
A comet is an icy small Solar System body that, when close enough to the Sun, displays a visible coma and sometimes also a tail. These phenomena are both due to the effects of solar radiation and the solar wind upon the nucleus of the comet...
s at virtually any time desired by the user. Often there is an option to find the velocities of the bodies of interest, as well.
Typically, such ephemerides cover several centuries, past and future; the future ones can be covered because celestial mechanics
Celestial mechanics
Celestial mechanics is the branch of astronomy that deals with the motions of celestial objects. The field applies principles of physics, historically classical mechanics, to astronomical objects such as stars and planets to produce ephemeris data. Orbital mechanics is a subfield which focuses on...
is an accurate theory. Nevertheless, there are secular phenomena
Secular phenomena
In astronomy, secular phenomena are contrasted with phenomena observed to repeat periodically. In particular, astronomical ephemerides use secular to label the longest-lasting or non-oscillatory perturbations in the motion of planets, as opposed to periodic perturbations which exhibit repetition...
which cannot adequately be considered by ephemerides. The biggest uncertainties on planetary positions are due to the perturbations of numerous asteroids, most of whose masses and orbits are poorly known, rendering their effect uncertain. Reflecting the continuing influx of new data and observations, the JPL has to revise its published ephemerides at intervals of 20 years.
Solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
ephemerides are essential for the navigation of spacecraft
Spacecraft
A spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
and for all kinds of space observations of the planets, their natural satellite
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
s, star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
s and galaxies.
Scientific ephemerides for sky observers mostly contain the position of the mentioned celestial body in right ascension
Right ascension
Right ascension is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. The other coordinate is the declination.-Explanation:...
and declination
Declination
In astronomy, declination is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. Declination in astronomy is comparable to geographic latitude, but projected onto the celestial sphere. Declination is measured in degrees north and...
, because these coordinates are the most often used on star maps and telescopes. The equinox
Equinox (celestial coordinates)
-Overview:In astronomy, equinox is a moment in time at which the vernal point, celestial equator, and other such elements are taken to be used in the definition of a celestial coordinate system. The position at other equinoxes can be computed by taking into account precession, nutation and...
of the coordinate system must be given. It is in nearly all cases either the actual equinox (the equinox valid for that moment, often referred to as "of date" or "current"), or that of one of the "standard" equinoxes, typically J2000.0, B1950.0, or J1900. Star maps are almost always in one of the standard equinoxes.
Scientific ephemerides often contain further useful data about the moon, planet, asteroid, or comet beyond the pure coordinates in the sky, such as elongation to the sun, brightness, distance, velocity, apparent diameter in the sky, phase angle, times of rise, transit, and set, etc.
Ephemerides of the planet Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
also sometimes contain the apparent inclination of its ring.
An ephemeris is usually only correct for a particular location on the Earth. In many cases the differences are too small to matter, but for nearby asteroids or the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
they can be quite important.
Global Positioning System
Global Positioning System
The Global Positioning System is a space-based global navigation satellite system that provides location and time information in all weather, anywhere on or near the Earth, where there is an unobstructed line of sight to four or more GPS satellites...
(GPS) navigation satellites transmit electronic ephemeris data consisting of health and exact location data that GPS receivers then use (together with the signal's elapsed travel time to the receiver) to calculate their own location on Earth using trilateration
Trilateration
In geometry, trilateration is the process of determinating absolute or relative locations of points by measurement of distances, using the geometry of circles, spheres or triangles. In addition to its interest as a geometric problem, trilateration does have practical applications in surveying and...
.
Other modern ephemerides recently created are the EPM due to the Russian Institute for Applied Astronomy of the Russian Academy of Sciences, and the INPOP ones by the French IMCCE.
Astrological ephemeris
The majority of astrologers study tropical astrology, involving planetary positions referenced to the vernal (spring) equinoxEquinox
An equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...
position along the ecliptic (the equinox being the center of Earth's rotational plane and Earth's orbital plane around the Sun). They use exactly the same referential frame of the astronomers, except for astrologers who study sidereal astrology
Sidereal astrology
Sidereal and tropical are astronomical terms used to describe two different definitions of a "year". They are also used as terms for two systems of ecliptic coordinates used in astrology....
(Indian Astrology) and use a different ephemerids, based on the constellations.
Though astrology
Astrology
Astrology consists of a number of belief systems which hold that there is a relationship between astronomical phenomena and events in the human world...
is and always has been geocentric, heliocentric astrology
Heliocentric Astrology
Heliocentric astrology is a method of astrology based on birth charts where the Sun is at the center.Standard forms of astrology are geocentric and the geocentric birth chart is drawn with the Earth at the center, and the planets are placed around the cartwheel in the positions that they would...
is an emerging field; for this purpose a standard ephemeris cannot be utilized, and because of this specialized heliocentric ephemerides must be calculated and used instead of the default geocentric ephemerides that are used in standard Western astrology
Western astrology
Western astrology is the system of astrology most popular in Western countries. Western astrology is historically based on Ptolemy's Tetrabiblos , which in turn was a continuation of Hellenistic and ultimately Babylonian traditions....
to construct the astrological chart/natal chart
Natal chart
In astrology, a natal chart is a stylized map of the universe with the "native" at the center. It is calculated for the exact time and location of the native's birth for the purposes of gaining insight into the native's personality and potential...
.
See also
- The Astronomical AlmanacAstronomical AlmanacThe Astronomical Almanac is an almanac published by the United States Naval Observatory and Her Majesty's Nautical Almanac Office, containing solar system ephemeris and catalogs of selected stellar and extragalactic objects....
(new name) - American Ephemeris and Nautical AlmanacAmerican Ephemeris and Nautical AlmanacThe American Ephemeris and Nautical Almanac was published for the years 1855 to 1980, containing information necessary for astronomers, surveyors, and navigators...
(old name) - Ephemeris timeEphemeris timeThe term ephemeris time can in principle refer to time in connection with any astronomical ephemeris. In practice it has been used more specifically to refer to:...
- Epoch (astronomy)Epoch (astronomy)In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as celestial coordinates, or elliptical orbital elements of a celestial body, where these are subject to perturbations and vary with time...
- Epoch (reference date)Epoch (reference date)In the fields of chronology and periodization, an epoch is an instance in time chosen as the origin of a particular era. The "epoch" then serves as a reference point from which time is measured...
- January 0 or March 0
- Jet Propulsion Laboratory Development Ephemeris
- DE400DE400DE400 are designations for the more recent members of a series of astronomical ephemerides produced by numerical integration at the Jet Propulsion Laboratory...
- AlmanacAlmanacAn almanac is an annual publication that includes information such as weather forecasts, farmers' planting dates, and tide tables, containing tabular information in a particular field or fields often arranged according to the calendar etc...
External links
- The JPL HORIZONS online ephemeris
- Introduction to the JPL ephemerides
- The effect of asteroidal perturbations on the long term accuracy of ephemerides
- Kharin, A. and Kolesnik, Y.; On the Errors of the Ephemerides Derived from Optical Observations of Planets. (1990), IAUIAUIAU may refer to:*International Astronomical Union*International American University*International American University College of Medicine*International Association of Universities*International Association of Ultrarunners...
SYMP.141 P.189, 1989. - Source code for computing ephemerides in C++ - by Steve Moshier
- Source code for easy and accurate ephemerides and charts in Java - by Tomás Alonso
- Interactive orrery and ephemeris provided by Fourmilab in Switzerland.
- Daily ephemeris, at the TAU AstroClub web site
- JavaScript Ephemeris
- The Photographer’s Ephemeris Adobe AIR application
Astrology links
- A Free 6000 Year Ephemeris Provided by Astro.com -- Based on Swiss Ephemeris, by Astrodienst ZürichZürichZurich is the largest city in Switzerland and the capital of the canton of Zurich. It is located in central Switzerland at the northwestern tip of Lake Zurich...
, SwitzerlandSwitzerlandSwitzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
(available in 8 languages) - The Original 3,000 Year High-Precision Daily Astrological Online Ephemeris from Khaldea.com -- 600BC to 2400AD—Calculated for MidnightMidnightMidnight is the transition time period from one day to the next: the moment when the date changes. In the Roman time system, midnight was halfway between sunset and sunrise, varying according to the seasons....
GMT; also with an AspectarianAstrological aspectIn astrology, an aspect is an angle the planets make to each other in the horoscope, and also to the ascendant, midheaven, descendant, lower midheaven, and other points of astrological interest. Aspects are measured by the angular distance in degrees and minutes of ecliptic longitude between two...
included for years 1900 to 2005