Precession of the equinoxes refers to the precession of the Earth's axis of rotation.

Precessional movement.

Precession of rotational axis relative to the direction to the Sun at perihelion and aphelion. ... Precession of rotational axis relative to the direction to the Sun at perihelion and aphelion. ...

Precession

The Earth goes through one complete precession cycle in a period of approximately 25,800 years, during which the positions of stars as measured in the equatorial coordinate system slowly change. The change in celestial coordinates in relation to earth's topographic coordinates is due to the rotation of the earth's inclined axis of rotation in space, a retrograde motion in relation to orbit direction. As a result, the year is shorter than solar orbit by the inverse of the precession period. A year is complete when the axis of rotation returns to the same direction in relation to the sun. Over the precession cycle, the Earth's north axial pole moves from where it is now pointing, within 1° of Polaris, in a circle around the ecliptic pole, with a current angular radius of 23 degrees 27 arcminutes ^[1], or about 23.5 degrees. The shift is 1 degree in 71.6 years (the angle is taken from the observer, not from the center of the circle). Precession refers to a change in the direction of the axis of a rotating object. ... The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ... The equatorial coordinate system is probably the most widely used celestial coordinate system, whose equatorial coordinates are: declination () right ascension () or hour angle () It is the most closely related to the geographic coordinate system, because they use the same fundamental plane, and the same poles. ... Polaris (α UMi / α Ursae Minoris / Alpha Ursae Minoris) is the brightest star in the constellation Ursa Minor. ...

The explanation of this is: The axis of the Earth undergoes precession due to a combination of the Earth's nonspherical shape (it is an oblate spheroid, bulging outward at the equator) and the gravitational tidal forces of the Moon and Sun applying torque as they attempt to pull the equatorial bulge into the plane of the ecliptic. The portion of the precession due to the combined action of the Sun and the Moon is called lunisolar precession. Earth is the current Good Article Collaboration of the week! Please help to improve this article to the highest of standards. ... An oblate spheroid is ellipsoid having a shorter axis and two equal longer axes. ... Bulk composition of the moons mantle and crust estimated, weight percent Oxygen 42. ... The Sun is the star at the center of Earths solar system. ... An equatorial bulge is a planetological term which describes a bulge which a planet may have around its equator, distorting it into an oblate spheroid. ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ...

Precession of the Earth's axis projected to the north celestial sphere

Image File history File links Download high resolution version (1000x920, 86 KB) Summary Path of North Celestial Pole Redraw of Image:Precession starchart. ... Image File history File links Download high resolution version (1000x920, 86 KB) Summary Path of North Celestial Pole Redraw of Image:Precession starchart. ...

A changing north star

Polaris is not particularly well-suited for marking the north celestial pole, as its visual magnitude, which is variable, hovers around 2.1, fairly far down the list of brightest stars in the sky. On the other hand, in 3000 BC the faint star Thuban in the constellation Draco was the pole star; at magnitude 3.67 it is only one-fifth as bright as Polaris; today it is all but invisible in light-polluted urban skies. The brightest star known to have been North Star or to be predictable as taking that role in the future is the brilliant Vega in the constellation Lyra, which was the pole star around 12000 BC and will be again around the year AD 14,000. When viewed looking down onto the Earth from the north, the direction of precession is clockwise. When standing on Earth looking outward, the axis appears to move counter-clockwise across the sky. This sense of precession, against the sense of Earth's own axial rotation, is opposite to the precession of a top on a table. The reason is that the torques imposed on the Earth by the Sun and Moon act in the sense of trying to align its axis normal to the ecliptic, i.e. to stand up more vertically in regard to the ecliptic plane, while the torque on a top spinning on a hard surface acts in the sense of trying to make the top fall over, rather than to stand up straighter. Polaris (α UMi / α Ursae Minoris / Alpha Ursae Minoris) is the brightest star in the constellation Ursa Minor. ... The star (or star system) Thuban, also known as α Draconis (alpha Draconis), is a star in the constellation of Draco. ... Orion is a remarkable constellation, visible from most places on the globe at one time or another during the year. ... Draco (Latin for Dragon) is a far northern constellation that is circumpolar for many northern hemisphere observers. ... For other uses of the words Pole star and Polestar see Polestar (disambiguation). ... The North Star is a title of the star best suited for navigation northwards. ... Vega (also known as Alpha Lyrae or 3 Lyrae) is a star approximately 25. ... Lyra (Latin for Lyre) is one of the 48 constellations listed by Ptolemy, and is one of the 88 modern constellations recognized by the International Astronomical Union. ... The Upper Paleolithic (or Upper Palaeolithic) is the third and last subdivision of the Paleolithic or Old Stone Age as it is understood in Europe, Africa and Asia. ... In physics, torque can be thought of informally as rotational force. Torque is commonly measured in units of newton metres; although, centiNewton Meters (cNm), Foot Pounds (Lb-Ft), Inch Pounds (Lb-In) and Inch Ounces (Oz-In) are also frequently used expressions of torque. ... The Sun is the star at the center of Earths solar system. ... Bulk composition of the moons mantle and crust estimated, weight percent Oxygen 42. ... The plane of the ecliptic is well seen in this picture from the 1994 lunar prospecting Clementine spacecraft. ... In physics, torque can be thought of informally as rotational force. Torque is commonly measured in units of newton metres; although, centiNewton Meters (cNm), Foot Pounds (Lb-Ft), Inch Pounds (Lb-In) and Inch Ounces (Oz-In) are also frequently used expressions of torque. ...

Polaris is not exactly at the pole; any long-exposure unguided photo will show it having a short trail. It is close enough for most practical purposes, though. The south celestial pole precesses too, always remaining exactly opposite the north pole. The south pole is in a particularly bland portion of the sky, and the nominal south pole star is Sigma Octantis, which, while fairly close to the pole, is even weaker than Thuban -- magnitude 5.5, which is barely visible even under a properly dark sky. The precession of the Earth is not entirely regular due to the fact that the Sun and Moon are not in the same plane and move relative to each other, causing the torque they apply to Earth to vary. This varying torque produces a slight irregular motion in the poles called nutation. A photograph with an exposure time of 25 seconds In photography, exposure is the total amount of light allowed to fall on the sensor (photographic film or CCD) during the process of taking a photograph. ... Octans (Latin for octant) is an inconspicuous constellation introduced by Nicolas Louis de Lacaille. ... 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. ...

Precession of the Earth's axis is a very slow effect, but at the level of accuracy at which astronomers work, it does need to be taken into account. Note that precession has no effect on the inclination ("tilt") of the plane of the Earth's equator (and thus its axis of rotation) on its orbital plane. It is 23.5 degrees and precession does not change that. The inclination of the equator and rotation axis in relation to the ecliptic (solar orbit) does change due to gravitational torque, but its period is different (main period about 41000 years).

Effects of axial precession on the seasons

This figure illustrates the effects of axial precession on the seasons, relative to perihelion and aphelion. The precession of the equinoxes can cause periodic climate change (see Milankovitch cycles), because the hemisphere that experiences summer at perihelion and winter at aphelion (as the southern hemisphere does presently) is in principle prone to more severe seasons than the opposite hemisphere. Graph showing the effect of axial precession on seasons. ... Graph showing the effect of axial precession on seasons. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ... Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years Climate change refers to the variation in the Earths global climate or regional climates over time. ... Milankovitch cycles are the collective effect of changes in the Earths movements upon its climate, named after Serbian geophysicist Milutin Milanković. The eccentricity, axial tilt, and precession of the Earths orbit vary in several patterns, resulting in 100,000 year ice age cycles of the Quaternary glaciation over...

Hipparchus estimated Earth's precession around 130 BC, adding his own observations to those of Babylonian and Chaldean astronomers in the preceding centuries. In particular they measured the distance of the stars like Spica to the Moon and Sun at the time of lunar eclipses, and because he could compute the distance of the Moon and Sun from the equinox at these moments, he noticed that Spica and other stars appeared to have moved over the centuries. Hipparchus. ... Centuries: 3rd century BC - 2nd century BC - 1st century BC Decades: 180s BC 170s BC 160s BC 150s BC 140s BC - 130s BC - 120s BC 110s BC 100s BC 90s BC 80s BC Years: 135 BC 134 BC 133 BC 132 BC 131 BC - 130 BC - 129 BC 128 BC... Babylonia, named for its capital city, Babylon, was an ancient state in the south part of Mesopotamia (in modern Iraq), combining the territories of Sumer and Akkad. ... Chaldea, the Chaldees of the KJV Old Testament, was a Hellenistic designation for a part of Babylonia. ... The Pleiades star cluster A star is a massive body of plasma in outer space that is currently producing or has produced energy through nuclear fusion. ... Spica (α Vir / α Virginis / Alpha Virginis) is the brightest star in the constellation Virgo, and one of the brightest stars in the nighttime sky. ... An eclipse refers to the phenomenon of one body passing into the shadow cast by another body. ...

Precession causes the cycle of seasons (tropical year) to be about 20.4 minutes less than the period for the earth to return to the same position with respect to the stars as one year previously (sidereal year). This results in a slow change (one day per 71 calendar years) in the position of the sun with respect to the stars at an equinox. It is significant for calendars and their leap year rules. A tropical year is the length of time that the Sun, as viewed from the Earth, takes to return to the same position along the ecliptic (its path among the stars on the celestial sphere). ... The sidereal year is the time for the Sun to return to the same position in respect to the stars of the celestial sphere. ... An equinox in astronomy is the moment when the Sun passes over the equator. ... A calendar is a system for naming periods of time, typically days. ... 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. ...