Thus the coordinate systems most used in astronomy need their own date-reference because the coordinate systems of that type are themselves in motion, e. g. by the precession of the equinoxes, nowadays often resolved into precessional components, separate precessions of the equator and of the ecliptic.

The attitude of the spacecraft about its center of gravity was controlled to scan the celestial sphere in a regular precessional motion maintaining a constant inclination between the spin axis and the sun direction.

This succession of pole stars is a result of earth's precessional motion.

The Earth, in addition to its diurnal ( daily ) rotation upon its axis and annual rotation around the Sun, incurs a precessional motion involving a slow periodic shift of the axis itself: approximately one degree every 72 years.

The orbit of the Moon has two important such precessional motions.

Astrologers maintain that an astrological age is a product of the earth's slow precessional rotation and lasts for 2, 150 years, on average.

Also note that the daily rotation of the Earth around its axis is opposite to the precessional rotation.

Note that this is an astronomical description of the precessional movement and the vernal equinox position in a given constellation may not imply the astrological meaning of an Age carrying the same name, as they ( ages and constellations ) only have an exact alignment in the " first point of Aries ", meaning once in each ca.

The angle between the jets and the axis is around 20 °, and the precessional period is around 162. 5 days.

Alderamin is located near the precessional path traced across the celestial sphere by the Earth's north pole.

The notion that an ancient Egyptian priestly elite tracked the precessional cycle over many thousands of years plays a central role in the theories expounded by Robert Bauval and Graham Hancock in their 1996 book Keeper of Genesis.

The confusion originates with the astronomer Ptolemy, who " adopted the larger, erroneous, figure, with the result that henceforth the two versions of the Great Year-the Platonic Great Year, defined by the planets, and the precessional, defined by the stars-were to be increasingly confused.

Earth goes through one such complete precessional cycle in a period of approximately 26, 000 years or 1 ° every 72 years, during which the positions of stars will slowly change in both equatorial coordinates and ecliptic longitude.

Like Earth, all of the rocky planets have a small precessional rotation of their spin axis.

* 850 – Ahmad ibn Muhammad ibn Kathīr al-Farghānī ( Alfraganus ) gives values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun

* 850 — Ahmad ibn Muhammad ibn Kathīr al-Farghānī ( Alfraganus ) gives values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun

While their theory has not been widely accepted in academia, it anticipated the recent popular revival of interest in precessional archeoastronomy.

In particular, the rituals symbolised the " turning back " of the precessional cycle to a remote ancestral time known as Zep Tepi (" first time ") which, the authors calculate, dates to around 10, 500 BC.

One immediate objection to the theory was that the total insolation during a year does not vary at all during the precessional cycle, only its seasonal distribution.

In 1925 Thomas relativistically recomputed the precessional frequency of the doublet separation in the fine structure of the atom.

Al-Farghani gave revised values for the obliquity of the ecliptic, the precessional movement of the apogees of the sun and the moon, and the circumference of the earth.

It was discovered in 1725 and later explained by the third Astronomer Royal, James Bradley, who attributed it to the finite speed of light and the motion of Earth in its orbit around the Sun.

Because the comet's motion with respect to Jupiter was very small, it fell almost straight toward Jupiter, which is why it ended up on a Jupiter-centric orbit of very high eccentricitythat is to say, the ellipse was nearly flattened out.

Vector relationships for uniform circular motion ; vector Ω representing the rotation is normal to the plane of the orbit with polarity determined by the right-hand rule and magnitude dθ / dt.

The gravitational perturbations of the other bodies of the Solar System cause a much smaller motion of the plane of the Earth's orbit, and hence of the ecliptic, known as planetary precession.

Currently about 23 °. 4, it varies slightly due to motion of the plane of the Earth's orbit, and hence the ecliptic, with planetary precession.

The extended line of research that culminated in Astronomia nova ( A New Astronomy )— including the first two laws of planetary motion — began with the analysis, under Tycho's direction, of Mars ' orbit.

Finding that an elliptical orbit fit the Mars data, he immediately concluded that all planets move in ellipses, with the sun at one focus — Kepler's first law of planetary motion.

For instance, the motion of a spacecraft, regarding its orbit and attitude ( rotation ), is described by the relativistic theory of classical mechanics, while the analogous movements of an atomic nucleus are described by quantum mechanics.

The physics principle behind orbital resonance is similar in concept to pushing a child on a swing, where the orbit and the swing both have a natural frequency, and the other body doing the " pushing " will act in periodic repetition to have a cumulative effect on the motion.

If the heavier body is much more massive than the smaller, as for a satellite or small moon orbiting a planet or for the Earth orbiting the Sun, it is accurate and convenient to describe the motion in a coordinate system that is centered on the heavier body, and we say that the lighter body is in orbit around the heavier.

To reduce the chances that a faster-moving ( and thus closer ) object be mistaken for the new planet, Tombaugh imaged each region near its opposition point, 180 degrees from the Sun, where the apparent retrograde motion for objects beyond Earth's orbit is at its strongest.

The quantum theory of the atom was developed as an explanation for the electron remaining in its orbit, which could not be explained by Newton's laws of motion and Maxwell's laws of ( classical ) electromagnetism.

Pierre-Simon Laplace produced in 1786 a theoretical analysis giving a basis on which the Moon's mean motion should accelerate in response to perturbational changes in the eccentricity of the orbit of the Earth around the Sun.

It stays in orbit, and from Kepler's 3rd law it follows that its velocity actually decreases, so the tidal action on the Moon actually causes a deceleration, i. e. a negative acceleration (- 25. 858 ± 0. 003 "/ cy² ), of its motion across the celestial sphere.

If one could see a satellite in geostationary orbit, it would appear to hover at the same point in the sky, i. e., not exhibit diurnal motion, while the Sun, Moon, and stars would traverse the heavens behind it.

Triton's orbit is associated with two tilts, the inclination of Neptune's spin to Neptune's orbit, 30 °, and the inclination of Triton's orbit to Neptune's spin, 157 ° ( an inclination over 90 ° indicates retrograde motion ).

There are long double ridges of ice with central troughs bearing a strong resemblance to Europan lineae ( although they have a larger scale ), and which may have a similar origin, possibly shear heating from strike-slip motion along faults caused by diurnal tidal stresses experienced before Triton's orbit was fully circularized.

The few impact craters on Triton are almost all concentrated in the leading hemisphere — that facing the direction of the orbital motion — with the majority concentrated around the equator between 30 ° and 70 ° longitude, resulting from material swept up from orbit around Neptune.

A geostationary orbit is useful for communications because ground antennas can be aimed at the satellite without their having to track the satellite ’ s motion.

For a prograde rotator, this is in the direction of motion in its orbit, and causes the semi-major axis of the orbit to increase steadily ; the object spirals away from the Sun.

As it travels around its orbit, the " dusk " hemisphere which has been heated over a long preceding time period is invariably in the direction of orbital motion.

This took the form of a 9-page manuscript, " De motu corporum in gyrum " (" Of the motion of bodies in an orbit "): the title is shown on some surviving copies, although the ( lost ) original may have been without title.