The ecliptic and its relation to rotation axis, plane of orbit and axial tilt. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation The orbital plane of an object orbiting another is the geometrical plane in which the orbit is embedded. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane.

The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. Year 1994 ( MCMXCIV) was a Common year starting on Saturday (link will display full 1994 Gregorian calendar) Spacecraft design The spacecraft was an octagonal prism 188 m high and 1 A spacecraft is a Vehicle or machine designed for Spaceflight. 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 phenomenon known as planetshine occurs when reflected Sunlight from a Planet illuminates the dark side of one of its moons Typically this The Sun (Sol is the Star at the center of the Solar System.

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. More accurately, it is the intersection of a spherical surface, the celestial sphere, with the ecliptic plane, which is the geometric plane containing the mean orbit of the Earth around the Sun. In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius " In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 The Sun (Sol is the Star at the center of the Solar System. The ecliptic plane should be distinguished from the invariable ecliptic plane, which is perpendicular to the vector sum of the angular momenta of all planetary orbital planes, to which Jupiter is the main contributor. The invariable plane of a Planetary system is the plane passing through its Barycenter (center of mass which is perpendicular to its Angular momentum In Physics, the angular momentum of a particle about an origin is a vector quantity equal to the mass of the particle multiplied by the Cross product of the position The present ecliptic plane is inclined to the invariable ecliptic plane by about 1. 5°.

The name ecliptic is derived from being the place where eclipses occur. An eclipse is an astronomical event that occurs when one Celestial object moves into the shadow of another

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°26' which is known as the obliquity of the ecliptic. In Astronomy and Navigation, the celestial sphere is an imaginary rotating Sphere of "gigantic Radius " In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. The intersections of the equatorial and ecliptic planes with the celestial dome are great circles known as the celestial equator and the ecliptic respectively. A great circle is a Circle on the surface of a Sphere that has the same circumference as the sphere dividing the sphere into two equal Hemispheres. The intersection line of the two planes results in two diametrically opposite intersection points, known as the equinoxes. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle The equinox which the Sun passes from south to north is known as the vernal equinox or first point of Aries. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle An equinox is the event of the Sun passing over the Earth's equator in its annual cycle Ecliptic longitude, usually indicated with the letter λ, is measured from this point on 0° to 360° towards the east. Longitude (ˈlɒndʒɪˌtjuːd or ˈlɒŋgɪˌtjuːd symbolized by the Greek character Lambda (λ is the east-west Geographic coordinate measurement Ecliptic latitude, usually indicated with the letter β is measured +90° to the north or -90° to the south. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the 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. Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere A. , and declination, usually indicated with δ also measured +90° to the north or -90° to the south. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either Simple rotation formulas allow a conversion from α,δ to λ,β and back (see: ecliptic coordinate system). 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. Zodiac denotes an annual cycle of twelve stations along the Ecliptic, the apparent path of the sun across the heavens through the Constellations that divide the ecliptic 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. In common usage a constellation is a group of celestial bodies that are connected together in some arrangement typically stars to form a visible figure or picture The zodiac signs are very important to many astrologers. 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 Modern astronomers typically use other coordinate systems today (see below). Historically Astronomy was more concerned with the classification and description of phenomena in the sky while Astrophysics attempted to explain these phenomena

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. In Astronomy, Precession refers to the movement of the rotational axis of a body such as a planet with respect to Inertial space. 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. 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 (\delta

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. Astronomical year numbering is based on AD ( Anno Domini)/CE ( Common Era) year numbering but follows normal Decimal Integer numbering more strictly ) as follows:^[1]

• 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. Taurus (it looks like a bull (ˈtɔrəs bull, symbol, Unicode ♉ is one of the Constellations of the Zodiac. Aries ( ram, symbol, Unicode ♈ is one of the Constellations of the Zodiac. Pisces (ˈpaɪsiːz Fish (plural symbol, Unicode ♓ is a Zodiac Constellation which lies between Aquarius to the west and Aries Aquarius ( Water -bearer or cup-bearer is the eleventh sign of the Zodiac, situated between Capricornus and Pisces. Capricornus ( Latin for "horned (male Goat " or "goat horn " is one of the Constellations of the Zodiac. It passed along (but not into) a 'corner' of Cetus on 0°10' distance in year 1489. Cetus ( Κῆτος Kētos, referring to the sea monster Cetus) is a Constellation of the northern winter sky in the region known as the Water
• 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. Leo (ˈliːoʊ Lion, symbol, Unicode ♌ is a Constellation of the Zodiac. Cancer ( Crab, symbol, Unicode ♋ is one of the twelve Constellations of the Zodiac. Gemini (ˈgɛmɪnaɪ Twins, symbol, Unicode ♊ is one of the Constellations of the Zodiac known as "the twins" Taurus (it looks like a bull (ˈtɔrəs bull, symbol, Unicode ♉ is one of the Constellations of the Zodiac. Aries ( ram, symbol, Unicode ♈ is one of the Constellations of the Zodiac.
• The September equinox passed from Libra into Virgo in year -729, will pass into Leo in year 2439. Virgo ( Virgin, symbol, Unicode ♍ is a Constellation of the Zodiac. Leo (ˈliːoʊ Lion, symbol, Unicode ♌ is a Constellation of the Zodiac.
• 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. Capricornus ( Latin for "horned (male Goat " or "goat horn " is one of the Constellations of the Zodiac. Ophiuchus (Ὀφιοῦχος ˌɒfiːˈuːkəs 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. Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes An equinox is the event of the Sun passing over the Earth's equator in its annual cycle 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. Diurnal motion is an astronomical term referring to the apparent daily motion of Stars around the Earth, or more precisely around the two 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. Sidereal time is a measure of the position of the Earth in its rotation around its axis or time measured by the apparent Diurnal motion of the Vernal equinox Solar times are measures of the apparent position of the Sun on the Celestial sphere.

Because the distance between Sun and Earth varies slightly around the year, also the speed with which the Sun moves around the ecliptic is variable. For example, within one year, the Sun is north of the equator for about 186. 40 days, while it is 178. 24 days south of the equator.

The mean Sun crosses the equator around 20 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. A leap year (or intercalary year) is a year containing one or more extra days (or in the case of Lunisolar calendars an extra month in order to keep the It also shifts slowly over the centuries due to imperfections in the Gregorian calendar. The Gregorian calendar is the most widely used Calendar in the world today

Ecliptic longitude 90°, at right ascension 6 hours and a northern declination equal to the obliquity of the ecliptic (23. 44°), is reached around 21 June. This is the June solstice or summer solstice in the northern hemisphere and winter solstice in the southern hemisphere. Solstices occur twice a year when the tilt of the Earth's axis is most oriented toward or away from the Sun, causing the Sun to reach its northernmost and southernmost extremes 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. Cancer is the fourth Astrological sign in the Zodiac, originating from the constellation of Cancer. For the novel by Henry Miller, see Tropic of Cancer (novel. The Tropic of Cancer, or Northern tropic, is one of five The Tropics are centered on the Equator and limited in Latitude by the Tropic of Cancer in the northern hemisphere at approximately 23°26' (23 Ecliptic longitude 180°, right ascension 12 hours is reached around 22 September and marks the second equinox or first point of Libra. Libra is the seventh Astrological sign in the Zodiac, originating from the constellation 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 21 December. Capricorn is the tenth Astrological sign in the Zodiac, originating from the constellation of 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. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 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. A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded The Solar System consists of the Sun and those celestial objects bound to it by Gravity. Inclination in general is the Angle between a Reference plane and another plane or axis of direction g. Eris 44 degrees and Pallas 34 degrees). TemplateInfobox Planet. --> 2 Pallas (ˈpæləs, or as Παλλάς) is one of the largest

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. An orbital node is one of the two points where an Orbit crosses a Plane of reference which it is inclined to An orbital node is one of the two points where an Orbit crosses a Plane of reference which it is inclined to An orbital node is one of the two points where an Orbit crosses a Plane of reference which it is inclined to Only when an inferior planet passes through one of its nodes can a transit over the Sun take place. The terms " inferior planet " and " superior planet " were originally used in the Ptolemaic Cosmology to differentiate those planets

Inclination and nodal lines, as almost all other orbital elements, change slowly over the centuries due to perturbations from the other planets.

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. Nutation is a slight irregular motion (etymologically a "nodding" in the Axis of rotation of a largely axially symmetric object such as a Gyroscope At a major lunar standstill, which takes place every 186 years the range of the Declination of the Moon reaches a maximum 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 article is about the lunar phase for other uses see New Moon (disambiguation. A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured Full moon is a Lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun. A lunar eclipse occurs whenever the Moon passes through some portion of the Earth's shadow This was the way the ancients could trace the ecliptic along the sky; they marked the places where eclipses could occur.

Ecliptic and star coordinates

Up to the 17th century in Europe, starmaps and positions in star catalogues were always given in ecliptical coordinates though in China, astronomers employed an equatorial system in their catalogues. 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. Conjunction is a term used in Positional astronomy and Astrology.

Also see zodiacal coordinates. Zodiac denotes an annual cycle of twelve stations along the Ecliptic, the apparent path of the sun across the heavens through the Constellations that divide the ecliptic

References

External links

• NASA: "The Path of the Sun, the Ecliptic"
• Orbits and the Ecliptic Plane
• The Ecliptic: the Sun's Annual Path