In order to maintain this alignment, Hindu astrology uses an adjustment, called ayanamsa, to take into account the gradual precession of the vernal equinox ( the gradual shift in the orientation of the Earth's axis of rotation ).

He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's.

The idea that immediately suggested itself was that the star's declination varied because of short-term changes in the orientation of the Earth's axis relative to the celestial sphere – a phenomenon known as nutation.

He fundamentally defined his arbitrary orientation for the cell as being that in which the internal current would run parallel to and in the same direction as a hypothetical magnetizing current loop around the local line of latitude which would induce a magnetic dipole field oriented like the Earth's.

Earth's rate of rotation must be integrated to obtain time, which is Earth's angular position ( specifically, the orientation of the meridian of Greenwich relative to the fictitious mean sun ).

See Earth's location in the universe for an orientation.

The seasons occur because the Earth's axis of rotation is not perpendicular to its orbital plane ( the “ plane of the ecliptic ”) but currently makes an angle of about 23. 44 ° ( called the " obliquity of the ecliptic "), and because the axis keeps its orientation with respect to an inertial frame of reference.

Later instruments of the " astatic " type used opposing magnets to become independent of the Earth's field and would operate in any orientation.

Newer calculations showed that if the Starfish Prime warhead had been detonated over the northern continental United States, the magnitude of the EMP would have been much larger ( 22 to 30 kilovolts / metre ) because of the greater strength of the Earth's magnetic field over the United States, as well as the different orientation of the Earth's magnetic field at high latitudes.

According to the standard reference text on nuclear weapons effects published by the U. S. Department of Defense, " The peak electric field ( and its amplitude ) at the Earth's surface from a high-altitude burst will depend upon the explosion yield, the height of the burst, the location of the observer, and the orientation with respect to the geomagnetic field.

On a larger time-scale, cyclic changes in climate and sea level are caused by Milankovitch cycles: cyclic changes in the orientation and / or position of the Earth's rotational axis and orbit around the Sun.

Relatively small changes in the orientation of the Earth's axis or length of the seasons can be a major influence on the Earth's climate.

For this reason, to simplify the description of Earth's orientation in astronomy and geodesy, it is conventional to chart the positions of the stars in the sky according to right ascension and declination, which are based on a frame that follows the Earth's precession, and to keep track of Earth's rotation, through sidereal time, relative to this frame as well.

In particular, it refers to the gradual shift in the orientation of Earth's axis of rotation, which, like a wobbling top, traces out a pair of cones joined at their apices in a cycle of approximately 26, 000 years ( called a Great or Platonic Year in astrology ).

( In actuality, other effects also slowly change the shape and orientation of the Earth's orbit, and these, in combination with precession, create various cycles of differing periods ; see also Milankovitch cycles.

The magnitude of the Earth's tilt, as opposed to merely its orientation, also changes slowly over time, but this effect is not attributed directly to precession.

Hamal's orientation with relation to the Earth's orbit around the Sun gives it a certain importance not apparent from its modest brightness.

* Variations in the Earth's orientation and length of day.

The modern Cartesian coordinate system in two dimensions ( also called a rectangular coordinate system ) is defined by an ordered pair of perpendicular lines ( axes ), a single unit of length for both axes, and an orientation for each axis.

Choosing a Cartesian coordinate system for a three-dimensional space means choosing an ordered triplet of lines ( axes ), any two of them being perpendicular ; a single unit of length for all three axes ; and an orientation for each axis.

The usual way of orienting the axes, with the positive x-axis pointing right and the positive y-axis pointing up ( and the x-axis being the " first " and the y-axis the " second " axis ) is considered the positive or standard orientation, also called the right-handed orientation.

* Director, the spatial and temporal average of the orientation of the long molecular axis within a small volume element of liquid crystal

# Inertial reference systems, where the coordinate axes retain their orientation relative to the fixed stars, or equivalently, to the rotation axes of ideal gyroscopes ; the axis points to the vernal equinox

Precession is a change in the orientation of the rotational axis of a rotating body.

For a generic solid object without any axis of symmetry, the evolution of the object's orientation, represented ( for example ) by a rotation matrix that transforms internal to external coordinates, may be numerically simulated.

The raised areas of the rifling are called " lands ," which make contact with the projectile ( for small arms usage, called a bullet ), imparting spin around an axis corresponding to the orientation of the weapon.

A beam may, for example, have an elliptical cross section, in which case the orientation of the beam diameter must be specified, for example with respect to the major or minor axis of the elliptical cross section.

A beam may, for example, have an elliptical cross section, in which case the orientation of the beam divergence must be specified, for example with respect to the major or minor axis of the elliptical cross section.

The rotor will maintain its spin axis direction regardless of the orientation of the outer frame.

A magnetometer determines the orientation of the generated field, which is interpolated to determine the axis of rotation.

For example, those used in the Gravity Probe B experiment measured changes in gyroscope spin axis orientation to better than 0. 5 milliarcseconds ( 1. 4 degrees ) over a one-year period.

When it is spun up to speed with its axis pointing in some direction, due to the law of conservation of angular momentum, such a wheel will normally maintain its original orientation to a fixed point in outer space ( not to a fixed point on Earth ).

This axis orientation is considered to be a point of minimum potential energy.

The crystal is cut into a plate, with the orientation of the cut chosen so that the optic axis of the crystal is parallel to the surfaces of the plate.

The amplitude and phase of this oscillation is proportional to the orientation of the spin axis relative to the Earth direction.

Subsequent work by Hale demonstrated a strong tendency for east-west alignment of magnetic polarities in sunspots, with mirror symmetry across the solar equator ; and that the magnetic polarity for sunspots in each hemisphere switched orientation, from one sunspot cycle to the next.

The celestial equator and the ecliptic are slowly moving due to perturbing forces on the Earth, therefore the orientation of the primary direction, their intersection at the Northern Hemisphere vernal equinox, is not quite fixed.

) When the axis precesses from one orientation to another, the equatorial plane of the Earth ( indicated by the circular grid around the equator ) moves.

The positions of the poles and equator on Earth do not change, only the orientation of the Earth against the fixed stars.

The only points where the pendulum returns to its original orientation after one day are the poles and the equator.

Subsequent work demonstrated a strong tendency for east-west alignment of magnetic polarities in sunspots, with mirror symmetry across the solar equator ; and that the polarity in each hemisphere switched orientation from one sunspot cycle to the next.