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Precession refers to a change in the direction of the axis of a rotating object. In physics, there are two types of precession, torque-free and torque-induced, the latter being discussed here in more detail. In certain contexts, "precession" may refer to the precession that the Earth experiences, the effects of this type of precession on astronomical observation, or to the precession of orbital objects.
Torque-free precession Only solid objects can be in torque-free precession. For example, when a plate is thrown, the plate may have some rotation around an axis that is not its axis of symmetry. When the object is not perfectly solid, internal vortices will tend to damp torque-free precession. This is an article on the real vortex phenomena. ...
Torque-induced precession Torque-induced precession (gyroscopic precession) is the phenomenon by which the axis of a spinning object (e.g. a part of a gyroscope) "wobbles" when a torque is applied to it. The phenomenon is commonly seen in a spinning toy top, but all rotating objects can undergo precession. If the speed of the rotation and the magnitude of the torque are constant the axis will describe a cone, its movement at any instant being at right angles to the direction of the torque. In the case of a toy top, if the axis is not perfectly vertical the torque is applied by the force of gravity trying to tip it over. A rolling wheel will tend to remain upright due to precession. When the wheel tilts to one side, the particles at the top are pushed to one side and the particles at the bottom are pushed the other way. However, since the wheel is rotating, these particles eventually switch places and cancel one another out. Precession or gyroscopic considerations have an effect on bicycle performance at high speed. Precession is also the mechanism behind gyrocompasses. The axis of rotation of a rotating body is a line such that the distance between any point on the line and any point of the body remains constant under the rotation. ...
This article does not cite its references or sources. ...
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. ...
This article is about the toy. ...
In physics, a net force acting on a body causes that body to accelerate; that is, to change its velocity. ...
Gravity is a force of attraction that acts between bodies that have mass. ...
This racing bicycle is built using lightweight, shaped aluminium tubing and carbon fiber stays and forks. ...
Cutaway of Anschütz gyrocompass The following description refers to the gyrocompasses used on ships. ...
This concept is easier to understand by examining the effects of inertia, which is often stated by the phrase "A body in motion tends to stay in motion." In this case the "motion" of a rotating body is in its rotation. If an external force pushes upon the rotating body, the body will resist the force by pushing back against it, but the reaction is delayed. The principle of inertia is one of the fundamental laws of classical physics which are used to describe the motion of matter and how it is affected by applied forces. ...
Gyroscopic precession also plays a large role in the flight controls on helicopters. Since the driving force behind helicopters is the rotor head (which rotates), gyroscopic precession comes into play. If the rotor head is tilted to the right, its counter-clockwise movement forces the aircraft to fly forward. To ensure the pilot's inputs are correct the aircraft has corrective linkages which tilt the rotor head to the right when the pilots push the "cyclic stick" forward, or to the left when the stick is pulled to the back.
The physics of precession Precession is because the resultant of the angular velocity of rotation and the angular velocity produced by the torque is an angular velocity about a line which makes an angle with the permanent rotation axis, and this angle lies in a plane at right angles to the plane of the couple producing the torque. The permanent axis must turn towards this line, since the body cannot continue to rotate about any line which is not a principal axis of maximum moment of inertia; that is, the permanent axis turns in a direction at right angles to that in which the torque might be expected to turn it. If the rotating body is symmetrical and its motion unconstrained, and if the torque on the spin axis is at right angles to that axis, the axis of precession will be perpendicular to both the spin axis and torque axis. Under these circumstances the period of precession is given by: Angular velocity describes the speed of rotation. ...
The principle of inertia is one of the fundamental laws of classical physics which are used to describe the motion of matter and how it is affected by applied forces. ...
 In which Is is the moment of inertia, Ts is the period of spin about the spin axis, and Q is the torque. In general the problem is more complicated than this, however. Moment of inertia (SI unit kilogram metre squared kg m2) quantifies the rotational inertia of an object, i. ...
For a layman’s explanation of Precession: we will have to imagine the wheel of a gyroscope as a group of particles that are being forced to move in circle. Remember the particles want to move in a straight line. In order for the particles to move in a curved line there must be a force. This force is provided by the structure of the wheel holding the particles within the wheel.
Now let’s see what happens to our accelerating particles when a torque is applied to the spinning wheel. Assume the axis of rotation created by the torque is through the center of the wheel at 90 degrees to the primary rotation of the wheel. Let’s look at a particle that is on this axis of rotation. Since the particle is on the axis of rotation there is no direct motion applied to the particle at the instant of the applied torque. But let’s look at what will need to happen at the next moment in time. The particle is now going to be forced to curve again. This time in the direction of the curve is to accommodate the tilt of the wheel. Now we have a particle that is already moving and it wants to keep moving in a straight line. So the particle will exert a force on the wheel. If you look at a particle on the other side of the wheel you will see that the force of the second particle is in the opposite direction of the first particle. That pair of unmatched forced is what causes the precession torque that is 90 degrees to the applied torque.
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 will slowly change; the change is actually due to the change of the coordinates. Over this cycle the Earth's north axial pole moves from where it is now, within 1° of Polaris, in a circle around the ecliptic pole, with an angular radius of 23 degrees 27 arcminutes [1], or about 23.5 degrees. The shift is 1 degree in 180 years (the angle is taken from the observer, not from the center of the circle). An equinox in astronomy is the moment when the Sun passes over the equator. ...
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. ...
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 third planet in the Sol system. ...
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 spectral type G2V yellow 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. ...
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. ...
Pierce this website is not very reliable!!!!!!!!!!!!!!!!! Some well-known constellations contain striking and familiar patterns of bright stars. ...
Draco (Latin for Dragon) is a far northern constellation that is circumpolar for many northern hemisphere observers. ...
The North Star is a title of the star best suited for navigation northwards. ...
Vega (α Lyr / α Lyrae / Alpha Lyrae) is the brightest star in the constellation Lyra, and the fifth brightest star in the sky. ...
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 spectral type G2V yellow 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. ...
 Image File history File links Download high resolution version (1000x920, 86 KB) Summary Path of North Celestial Pole Redraw of Image:Precession starchart. ...
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 on the ecliptic does change due to gravitational torque, but its period is different (main period about 41000 years).
The following 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. 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 is the name given to the collective effect of changes in the Earths movements upon its climate. ...
 Graph showing the effect of axial precession on seasons. ...
[2]
Hipparchus first 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 (Greek ) (ca. ...
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. ...
Precession of planetary orbits The revolution of a planet in its orbit around the Sun is also a form of rotary motion. (In this case, the combined system of Earth and Sun is rotating.) So the axis of a planet's orbital plane will also precess over time. Stylized and exaggerated picture of the precession of the orbit of a planet around the sun. ...
Stylized and exaggerated picture of the precession of the orbit of a planet around the sun. ...
This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...
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. ...
The Sun is the spectral type G2V yellow star at the center of Earths solar system. ...
The major axis of each planet's elliptical orbit also precesses within its orbital plane, in response to perturbations in the form of the changing gravitational forces exerted by other planets. This is called perihelion precession. Discrepancies between the observed perihelion precession rate of the planet Mercury and that predicted by classical mechanics were prominent among the forms of experimental evidence leading to the acceptance of Einstein's Theory of Relativity, which predicted the anomalies accurately.[3] Atmospheric characteristics Atmospheric pressure trace Potassium 31. ...
It has been suggested that this article or section be merged with Newtonian mechanics. ...
To meet Wikipedias quality standards, this article may require cleanup. ...
Wikisource has original text related to this article: Relativity: The Special and General Theory Albert Einsteins theory of relativity, or simply relativity, refers specifically to two theories: special relativity and general relativity. ...
It is generally understood that the gravitational pulls of the sun and the moon cause the precession of the equinoxes on Earth which operate on cycles of 23,000 and 19,000 years. The precession of the orbit of the Earth is an important part of the astronomical theory of ice ages. Milankovitch cycles is the name given to the collective effect of changes in the Earths movements upon its climate. ...
Variations in CO2, temperature and dust from the Vostok ice core over the last 400 000 years For the animated movie, see Ice Age (movie). ...
Precession is also an important consideration in the dynamics of atoms and molecules. Properties In chemistry and physics, an atom (Greek άτομον meaning indivisible) is the smallest possible particle of a chemical element that retains its chemical properties. ...
In general, a molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. ...
See also Geometric precession is the term used to describe the Earth’s changing orientation to inertial space not caused by local forces. ...
Larmor precession refers to the precession of the magnetic moments of electrons or atomic nucleii in atoms around the direction of an external magnetic field. ...
This article needs to be wikified. ...
Thomas precession, named after L.H. Thomas, is a correction to the spin-orbit interaction in Quantum Mechanics, which takes into account the relativistic time dilation between the electron and the nucleus in hydrogenic atoms. ...
External links
Notes 1 ↑ Cook, David R. (1999), "U.S. Department of Energy, Environmental Earth Science Archive, Ask A Scientist" [4]
3 ↑ Max Born (1924), Einstein's Theory of Relativity (The 1962 Dover edition, page 348 lists a table documenting the observed and calculated values for the precession of the perihelion of Mercury, Venus, and Earth.) Max Born Max Born (born December 11, 1882 in Breslau, died January 5, 1970 in Göttingen) was a German mathematician and physicist of Jewish heritage. ...
1924 (MCMXXIV) was a leap year starting on Tuesday (link will take you to calendar). ...
References - "Moon and Spica", StarDate July 14, 2005, University of Texas McDonald Observatory, [5]
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