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Encyclopedia > Ecliptic
The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. Clementine's camera reveals (from right to left) the Moon lit by Earthshine, the Sun's glare rising over the Moon's dark limb, and the planets Saturn, Mars and Mercury (the three dots at lower left).
The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. Clementine's camera reveals (from right to left) the Moon lit by Earthshine, the Sun's glare rising over the Moon's dark limb, and the planets Saturn, Mars and Mercury (the three dots at lower left).

The ecliptic is the apparent path that the Sun traces out along the sky, in relation to the stars, throughout the course of the year. More accurately, 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. It should be distinguished from the invariable ecliptic plane, which is the vector sum of the angular momenta of all planetary orbital planes, to which Jupiter is the main contributor. Image File history File linksMetadata Ecliptic. ... Image File history File linksMetadata Ecliptic. ... 1994 (MCMXCIV) was a common year starting on Saturday of the Gregorian calendar, and was designated as the International Year of the Family and the International Year of the Sport and the Olympic Ideal by United Nations. ... Clementine was a joint space project between the Ballistic Missile Defense Organization (BMDO, previously the Strategic Defense Initiative Organization, or SDIO) and NASA. The objective of the mission was to test sensors and spacecraft components under extended exposure to the space environment and to make scientific observations of the Moon... The Space Shuttle Discovery as seen from the International Space Station. ... Apparent magnitude: up to -12. ... Leonardo da Vincis sketch of crescent Moon with earthshine as part of his Codex Leicester, written between 1506 and 1510. ... The Sun is the star at the center of the Solar System. ... Look up Limb in Wiktionary, the free dictionary. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... Note: This article contains special characters. ... The celestial sphere is divided by the celestial equator. ... Two intersecting planes in three-dimensional space In mathematics, a plane is a fundamental two-dimensional object. ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The Sun is the star at the center of the Solar System. ... The invariable plane of the solar system is the plane passing through its barycenter (center of mass) which is perpendicular to its angular momentum vector, about 98% of which is contributed by the orbital angular momenta of the four jovian planets (Jupiter, Saturn, Uranus, and Neptune). ... This gyroscope remains upright while spinning due to its angular momentum. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ...


The name ecliptic is derived from being the place where eclipses occur. This article discusses astronomical eclipses. ...

Contents

Ecliptic and equator

As the rotation axis of the Earth is not perpendicular to its orbital plane, the equatorial plane is not parallel to the ecliptic plane, but makes an angle of about 23°27' which is known as the obliquity of the ecliptic. The intersections of the equatorial and ecliptic plane with the celestial dome are great circles known as the celestial equator and the ecliptic. The intersection line of the two planes results in two diametrically opposite intersection points, known as the equinoxes. The equinox which the Sun passes from south to north is known as the vernal equinox or first point of Aries. Ecliptic longitude, usually indicated with the letter λ, is measured from this point on 0° to 360° towards the east. Ecliptic latitude, usually indicated with the letter β is measured +90° to the north or -90° to the south. The same intersection point also defines the origin of the equatorial coordinate system, named right ascension measured from 0 to 24 hours also to the east and usually indicated with α or R.A., and declination, usually indicated with δ also measured +90° to the north or -90° to the south. Simple rotation formulas allow a conversion from α,δ to λ,β and back (see: ecliptic coordinate system). In astronomy and navigation, the celestial sphere is an imaginary rotating sphere of gigantic radius, concentric with the Earth. ... The Obliquity of the ecliptic is the angle between the plane of the Earths equator and the ecliptic plane in which the Earth rotates around the Sun. ... A great circle is a circle on the surface of a sphere that has the same diameter as the sphere, dividing the sphere into two equal hemispheres. ... In astronomy, an equinox is defined as the moment when the sun reaches one of two intersections between the ecliptic and the celestial equator. ... A compass rose showing the cardinal directions Cardinal directions or cardinal points are the four principal directions or points of the compass in plane. ... A compass rose showing the cardinal directions Cardinal directions or cardinal points are the four principal directions or points of the compass in plane. ... Illumination of Earth by Sun on the day of equinox The vernal equinox (or spring equinox) marks the beginning of astronomical spring. ... The First Point of Aries, also called the vernal equinox point, is one of the two points on the celestial sphere where the celestial equator intersects the ecliptic. ... Longitude, sometimes denoted by the Greek letter λ (lambda),[1][2] describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. ... A compass rose showing the cardinal directions Cardinal directions or cardinal points are the four principal directions or points of the compass in plane. ... Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator. ... Equatorial Coordinates Right ascension (abbrev. ... In astronomy, declination (abbrev. ... The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane. ...


Ecliptic and stars

The ecliptic serves as the center of a region called the zodiac which constitutes a band of 9° on either side. Traditionally, this region is divided into 12 signs of 30° longitude each. By tradition, these signs are named after 12 of the 13 constellations straddling the ecliptic. The zodiac signs are very important to many astrologers. Modern astronomers typically use other coordinate systems today (see below). It has been suggested that this article be split into multiple articles. ... This article or section does not cite its references or sources. ... An astrological chart (or horoscope) _ Y2K Chart — This particular chart is calculated for January 1, 2000 at 12:01:00 A.M. Eastern Standard Time in New York City, New York, USA. (Longitude: 074W0023 - Latitude: 40N4251) Astrology (from Greek: αστρολ&#959... An astronomer or astrophysicist is a scientist whose area of research is astronomy or astrophysics. ...


The position of the vernal equinox is not fixed among the stars but due to the lunisolar precession slowly shifting westwards over the ecliptic with a speed of 1° per 72 years. A much smaller north/southwards shift can also be discerned, (the planetary precession, along the instantaneous equator, which results in a rotation of the ecliptic plane). Said otherwise the stars shift eastwards (increase their longitude) measured with respect to the equinoxes (in other words, as measured in ecliptic coordinates and (often) also in equatorial coordinates. Precession refers to a change in the direction of the axis of a rotating object. ... The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane. ... The equatorial coordinate system is probably the most widely used celestial coordinate system, whose equatorial coordinates are: declination () right ascension () -also RA-, or hour angle () -also HA- It is the most closely related to the geographic coordinate system, because they use the same fundamental plane, and the same poles. ...


Using the current official IAU constellation boundaries — and taking into account the variable precession speed and the rotation of the ecliptic — the equinoxes shift through the constellations in the Astronomical Julian calendar years (in which the year 0 = 1 BC, -1 = 2 BC, etc.) as follows:[1] Logo of the IAU The International Astronomical Union (French: Union astronomique internationale) unites national astronomical societies from around the world. ... Astronomical year numbering is another method of designating BC/AD years. ...

  • The March equinox passed from Taurus into Aries in year -1865, passed into Pisces in year -67, will pass into Aquarius in year 2597, will pass into Capricorn in year 4312. It passed along (but not into) a 'corner' of Cetus on 0°10' distance in year 1489.
  • The June solstice passed from Leo into Cancer in year -1458, passed into Gemini in year -10, passed into Taurus in December year 1989, will pass into Aries in year 4609.
  • The September equinox passed from Libra into Virgo in year -729, will pass into Leo in year 2439.
  • The December solstice passed from Capricorn into Sagittarius in year -130, will pass into Ophiuchus in year 2269, and will pass into Scorpius in year 3597.

Taurus (IPA: , Latin: , symbol , ) is one of the constellations of the zodiac. ... Aries (IPA: , Latin: , symbol , ) is one of the constellations of the zodiac. ... For other uses, see Pisces. ... Aquarius (IPA: , Latin: ) is the eleventh sign of the zodiac, situated between Capricornus and Pisces. ... Capricornus ( or , Unicode: ♑), a name meaning Horned Goat or That which has horns like a goats in Latin, is one of the constellations of the zodiac. ... Cetus (a name from Greek mythology, referring to a Whale or Sea monster, see Ceto) is a constellation of the southern sky, in the region known as the Water, near other watery constellations like Aquarius, Pisces, and Eridanus. ... Leo (IPA: , Latin: , symbol , ) is a constellation of the zodiac. ... Cancer (IPA: , Latin: , symbol , ) is one of the thirteen constellations of the zodiac. ... Gemini (IPA: , Latin: , symbol , ) is one of the constellations of the zodiac known as the twins . It is part of the winter sky, lying between Taurus to the west and the dim Cancer to the east, with Auriga and the near-invisible Lynx to the north and Monoceros and Canis... Taurus (IPA: , Latin: , symbol , ) is one of the constellations of the zodiac. ... Aries (IPA: , Latin: , symbol , ) is one of the constellations of the zodiac. ... Virgo (IPA: , Latin: , symbol , ) is a constellation of the zodiac. ... Leo (IPA: , Latin: , symbol , ) is a constellation of the zodiac. ... Capricornus ( or , Unicode: ♑), a name meaning Horned Goat or That which has horns like a goats in Latin, is one of the constellations of the zodiac. ... For other uses, see Sagittarius. ... Ophiuchus (IPA: ), formerly referred to as Serpentarius (IPA: ), both meaning serpent-holder, is one of the 88 constellations, and was also one of the 48 listed by Ptolemy. ... Scorpius (Latin for scorpion, symbol , Unicode ♏) is one of the constellations of the zodiac. ...

Ecliptic and Sun

Due to perturbations to the Earth's orbit by the other planets, the true Sun is not always exactly on the ecliptic, but may be some arcseconds north or south of it. It is therefore the centre of the mean Sun which outlines its path. As the Earth revolves in one year around the Sun, it appears that the Sun also needs one year to pass the whole ecliptic. With slightly more than 365 days in the year, the Sun moves almost 1° eastwards every day (direction of increasing longitude). This annual motion should not be confused with the daily motion of the Sun (and the stars, the whole celestial sphere for that matter) towards the west in 24 hours and along the equator. In fact where the stars need about 23h56m for one such rotation to complete, the sidereal day, the Sun, which has shifted 1° eastwards during that time needs 4 minutes extra to complete its circle, making the solar day just 24 hours. Diurnal motion is an astronomical term referring to the apparent daily motion of stars in orbit around the Earth, caused by the Earths rotation around its axis. ... On a prograde planet like the Earth, the sidereal day is shorter than the solar day. ... Solar time is based on the idea that, when the sun reaches its highest point in the sky, it is noon. ...


The mean Sun crosses the equator around 21 March in the vernal equinox, its declination, right ascension, and ecliptic longitude are all zero then (the ecliptic latitude is always). The March equinox marks the onset of spring in the northern hemisphere and autumn in the southern. As such the term "spring equinox" should be avoided. The actual date and time varies from year to year because of the occurrence of leap years. It also shifts slowly over the centuries due to imperfections in the Gregorian calendar. A leap year (or intercalary year) is a year containing an extra day or month in order to keep the calendar year in sync with an astronomical or seasonal year. ... The Gregorian calendar is the most widely used calendar in the world. ...


Ecliptic longitude 90°, at right ascension 6 hours and a northern declination equal to the obliquity of the ecliptic (23.44°), is reached around 22 June. This is the June solstice or summer solstice in the northern hemipshere and winter solstice in the southern hemisphere. It is also the first point of Cancer and directly overhead on Earth on the tropic of Cancer so named because the Sun turns around in declination. Ecliptic longitude 180°, right ascension 12 hours is reached around 23 September and marks the second equinox or first point of Libra. Due to perturbations to the Earth orbit, the moment the real Sun passes the equator might be several minutes earlier or later. The southern most declination of the sun is reached at ecliptic longitude 270°, right ascension 18 hours at the first point of the sign of Capricorn around 22 December. A solstice is either of the two events of the year when the sun is at its greatest distance from the equatorial plane. ... This article or section does not adequately cite its references or sources. ... World map showing the Tropic of Cancer The Tropic of Cancer (cancer is Latin for crab), or Northern tropic is one of the five major circles of latitude that mark maps of the Earth. ... The tropics are the geographic region of the Earth centered on the equator and limited in latitude by the two tropics: the Tropic of Cancer in the northern hemisphere and the Tropic of Capricorn in the southern hemisphere. ... This article or section does not cite its references or sources. ... Symbol of Capricorn Capricorn is an astrological sign, which is associated with the constellation Capricornus. ...


In any case it must be stressed that although these traditional signs (in western tropical astrology) have given their names to the solstices and equinoxes, in reality, (as from the list in the previous chapter) the cardinal points are currently situated in the constellations of Pisces, Taurus, Virgo and Sagittarius respectively. Tropical Astrology is a type of astrology based on a zodiac whose points of reference are the tropics. ...


Ecliptic and planets

Most planets go in orbits around the sun which are almost in the same plane as the Earth's orbital plane, differing by a few degrees at most. As such they always appear close to the ecliptic when seen in the sky. Mercury with an orbital inclination of 7° is an exception. Pluto, at 17°, was previously the exception until it was reclassified a dwarf planet, but other bodies in the Solar System have even greater orbital inclinations (e.g. Eris 44 degrees and Pallas 34 degrees). Note: This article contains special characters. ... Inclination in general is the angle between a reference plane and another plane or axis of direction. ... Adjectives: Plutonian Atmosphere Surface pressure: 0. ... Artists impression of Pluto (background) and Charon (foreground). ... Major features of the Solar System (not to scale, from left to right): Pluto, Neptune, Uranus, Saturn, Jupiter, the asteroid belt, the Sun, Mercury, Venus, Earth & Moon, and Mars. ... Inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit and is the angular distance of the orbital plane from the plane of the reference (usually planets equator or the ecliptic), stated in degrees. ... Eris (IPA pronunciation ) or ), also designated (136199) Eris or 136199 Eris (See Minor planet names), is the largest known dwarf planet in the solar system. ... 2 Pallas (IPA: ), Greek Παλλάς) is an asteroid located in the asteroid belt region of the solar system and was the second to be discovered. ...


The intersection line of the ecliptical plane and another planet's orbital plane is called the nodal line of that planet, and the nodal line's intersection points on the celestial sphere are the ascending node (where the planet crosses the ecliptic from south to north) and the diametrically opposite descending node. Only when an inferior planet passes through one of its nodes can a transit over the Sun take place. An orbital node is one of the two points where an inclined orbit crosses a plane of reference (e. ... The ascending node is one of the orbital nodes, a point in the orbit of an object where it crosses the plane of the ecliptic from the south celestial hemisphere to the north celestial hemisphere in the direction of motion. ... The descending node is the point in the orbit of an object where it crosses the plane of the ecliptic from the north celestial hemisphere to the south celestial hemisphere in the direction of motion. ... The terms inferior planet and superior planet were coined by Copernicus to distinguish a planets orbits size in relation to the Earths. ...


Inclination and nodal lines, as almost all other orbital elements, change slowly over the centuries due to perturbations from the other planets. Perturbation is a term used in astronomy to describe alterations to an objects orbit caused by gravitational interactions with other bodies. ...


Ecliptic and Moon

The orbit of the Moon is inclined by about 5° on the ecliptic. Its nodal line is not fixed either, but regresses (moves towards the west) over a full circle every 18.6 years. This is the cause of nutation and lunar standstill. The moon crosses the ecliptic about twice per month. If this happens during new moon a solar eclipse occurs, during full moon a lunar eclipse. This was the way the ancients could trace the ecliptic along the sky; they marked the places where eclipses could occur. Apparent magnitude: up to -12. ... Rotation (green), Precession (blue) and Nutation (red) of the Earth Nutation is a slight irregular motion (etymologically a nodding) in the axis of rotation of a largely axially symmetric object, such as a gyroscope or a planet. ... At a major lunar standstill, which takes place every 18. ... The lunar phase depends on the Moons position in orbit around Earth. ... Photo taken during the 1999 eclipse. ... Composite image of the Moon as taken by the Galileo spacecraft on 7 December 1992. ... A lunar eclipse occurs whenever the Moon passes through some portion of the Earths shadow. ...


Ecliptic and star coordinates

Up to the 17th century, starmaps and positions in star catalogues were always given in ecliptical coordinates. It was not until astronomers started to use telescopes to measure star positions that equatorial coordinates came in use, and so exclusively that nowadays ecliptical coordinates are no longer used. This is not always desirable. A planetary conjunction for example would be much more illustratively described by ecliptic coordinates than equatorial.


Also see zodiacal coordinates. It has been suggested that this article be split into multiple articles. ...


References

  1. ^ J. Meeus; Mathematical astronomical morsels; ISBN 0-943396-51-4

External links

Look up ecliptic in Wiktionary, the free dictionary.

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Ecliptic Illustration Multimedia (370 words)
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It should be distinguished from the invariable ecliptic plane which is the vector sum of the angular momenta of all planetary orbital planes, in which Jupiter is the main contributant.
Ecliptic latitude, usually indicated with the letter β is measured +90° to the north or -90° to the south.
The intersection line of the ecliptical plane and the orbital plane is called the nodal line, and the intersection points on the celestial sphere are the ascending node (where the planet crosses the ecliptic from south to north) and the diametrically opposite descending node.
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