Crossword clues for precession
The Collaborative International Dictionary
Precession \Pre*ces"sion\, n. [L. praecedere, praecessum, to go before: cf. F. pr['e]cession. See Precede.] The act of going before, or forward.
Lunisolar precession. (Astron.) See under Lunisolar.
Planetary precession, that part of the precession of the equinoxes which depends on the action of the planets alone.
Precession of the equinoxes (Astron.), the slow backward motion of the equinoctial points along the ecliptic, at the rate of 50.2[sec] annually, caused by the action of the sun, moon, and planets, upon the protuberant matter about the earth's equator, in connection with its diurnal rotation; -- so called because either equinox, owing to its westerly motion, comes to the meridian sooner each day than the point it would have occupied without the motion of precession, and thus precedes that point continually with reference to the time of transit and motion.
Douglas Harper's Etymology Dictionary
1590s, from Late Latin praecissionem (nominative praecissio) "a coming before," from past participle stem of Latin praecedere "to go before" (see precede). Originally used in reference to calculations of the equinoxes, which come slightly earlier each year.
Wiktionary
alt. 1 (context uncountable English) precedence 2 (context physics countable English) The wobbling motion of the axis of a spinning body when there is an external force acting on the axis. 3 (context astronomy uncountable English) The slow gyration of the earth’s axis around the pole of the ecliptic, caused mainly by the gravitational torque of the sun and moon. 4 Any of several slow changes in an astronomical body's rotational or orbital parameters. n. 1 (context uncountable English) precedence 2 (context physics countable English) The wobbling motion of the axis of a spinning body when there is an external force acting on the axis. 3 (context astronomy uncountable English) The slow gyration of the earth’s axis around the pole of the ecliptic, caused mainly by the gravitational torque of the sun and moon. 4 Any of several slow changes in an astronomical body's rotational or orbital parameters.
WordNet
n. the motion of a spinning body (as a top) in which it wobbles so that the axis of rotation sweeps out a cone
the act of preceding in time or order or rank (as in a ceremony) [syn: precedence, precedency]
Wikipedia
Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In other words, if the axis of rotation of a body is itself rotating about a second axis, that body is said to be precessing about the second axis. A motion in which the second Euler angle changes is called nutation. In physics, there are two types of precession: torque-free and torque-induced.
In astronomy, "precession" refers to any of several slow changes in an astronomical body's rotational or orbital parameters, and especially to Earth's precession of the equinoxes. (See section Astronomy below.)
Precession refers to a specific change in the direction of the rotation axis of a rotating object, in which the second Euler angle (angle of nutation) is constant
Precession may specifically mean:
- Precession is the name of one of the Euler rotations
- Axial precession (astronomy) — the precession of the Earth's axis of rotation (also known as the "precession of the equinoxes"), or similar
- de Sitter precession — a general relativistic correction to the precession of a gyroscope near a large mass such as the Earth
- Larmor precession — the precession of the magnetic moments of electrons, atomic nuclei, and atoms about an external magnetic field
- Lense-Thirring precession — a general relativistic correction to the precession of a gyroscope near a large rotating mass such as the Earth
- Precession (mechanical) — the process of one part rotating with respect to another due to fretting between the two
- Thomas precession — a special relativistic correction to the precession of a gyroscope in a rotating non-inertial frame
Precession can also refer to change in the direction of an axis other than an axis of rotation:
- Apsidal precession, perihelion precession, or orbital precession, the rotation of the orbit of a celestial body
Precession, also called epicyclic fretting precession, (or more accurately hypocyclic fretting precession since "epicyclic" applies to a round part spinning outside a circle and "hypocyclic" applies to a round part spinning inside a circle) is the process of a round part in a round hole rotating with respect to that hole because of clearance between them and a radial force on the part that changes direction. The direction of rotation of the inner part is opposite to the direction of rotation of the radial force. Fretting between the part and the hole is often a result of this motion. "In machinery, fretting is the micro-motion of tightly fitting parts that superficially appear immobile with respect to each other."
"For a pedal, a rotating load arises from downward pedaling force on a spindle rotating with its crank making the predominantly downward force effectively rotate about the pedal spindle. What may be less evident is that even tightly fitting parts have relative clearance due to their elasticity, metals not being rigid materials as is evident from steel springs. Under load, micro deformations, enough to cause motion, occur in such joints. This can be seen from wear marks where pedal spindles seat on crank faces."
This precession is a process purely due to contact forces and does not depend on inertia and is not inversely proportional to spin rate. It is completely unrelated to torque-free and torque-induced precession.
Usage examples of "precession".
Let us therefore not attempt to dislodge the Greek astronomer from his pedestal as the discoverer of precession unless we can find a significantly more accurate value recorded in a significantly more ancient source.
Arcturus: of the precession of equinoxes: of Orion with belt and sextuple sun theta and nebula in which 100 of our solar systems could be contained: of moribund and of nascent new stars such as Nova in 1901: of our system plunging towards the constellation of Hercules: of the parallax or parallactic drift of socalled fixed stars, in reality evermoving wanderers from immeasurably remote eons to infinitely remote futures in comparison with which the years, threescore and ten, of allotted human life formed a parenthesis of infinitesimal brevity.
He could imagine those shining rotors starting to turn, spinning faster and faster, spinning, precessing at right angles to all the dimensions of normal space, tumbling through the dark infinities, dragging the ship and all aboard her with them as the temporal precession field built up.
Richard slowly turned each over, idly looking for anything that made sense to him as Zedd droned on about overlapping transpositional forks and triple duplexes bound to conjugated roots compromised by precession and sequential, proportional, binary inversions shrouding flawed bifurcations that the formulas revealed which could only be detected through Subtractive levorotatory.
Since then, due to the precession of the equinoxes, the signs have changed.
At other times I was haunted in my nightly vigils by the problem of precession of the equinoxes, as calculated long ago by Hipparchus of Alexandria.
When the Sector arrives, they set up upon a Bluff overlooking Monon-gahela, and watch the Culmination of Stars in Lyra and Cygnus, correcting for seconds plus and minus of Aberration, Deviation, Precession, and Refraction, whilst in Cabins nearby the Wives of the new-hir'd Axmen gather, and those Axmen who may, come thro', and out the back, to take White Maize Whiskey out of a Tin Cup.
Also because of the phenomenon of the precession of the equinoxes, the four points on the colures (the two equinoxes and the two solstices) will appear to drift westwards at the very slow rate of 50.
But can chance account for the fact that these and other prime integers of precession keep cropping up in supposedly unrelated mythologies from all over the world, and in such stolid but enduring vehicles as calendar systems and works of architecture?
Incredible as it seems, the perimeter of the pyramid comes within 20 feet of equaling the diameter of the Earth, when our planet's dimensions are scaled down to a ratio equaling 1:43,200, numbers representing our mathematical code of precession.
The pole star by then, because of precession of the equinoxes, was a dim thing once called Gamma Cephei.
But if they were constructed by the Aoi, if they're that old, then because of the precession of the equinoxes it would have been other stars rising at that notch at this day and time of year, other threads of light laying the weft into the shed than the ones that rise in these days at this time.
The ones he studied were first, the 26,000-year precession of the equinoxes, resulting from the slow wobble of the Earth's axis.
Here in these galleries she had set her memory pictures of the cycles of the wandering stars and the precession of the equinoxes.
They might be driven by the precession of the equinoxes, a well-known motion akin to the slow, drifting precession of a rapidly spinning top.