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# Apparent place

The apparent place of an object is its position in space as seen by an observer. [1]

## Aberration of light

The aberration of light (also referred to as astronomical aberration, stellar aberration, or velocity aberration) is an astronomical phenomenon which produces an apparent motion of celestial objects about their true positions, dependent on the velocity of the observer.

## Astrometry

Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies.

## Astronomical Calculation Institute (Heidelberg University)

The Astronomical Calculation Institute (Astronomisches Rechen-Institut; ARI) is a research institute in Heidelberg, Germany, dating from the 1700s.

## Astronomy

Astronomy (from ἀστρονομία) is a natural science that studies celestial objects and phenomena.

## Atmosphere of Earth

The atmosphere of Earth is the layer of gases, commonly known as air, that surrounds the planet Earth and is retained by Earth's gravity.

## Atmospheric refraction

Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height.

## Axial precession

In astronomy, axial precession is a gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis.

## Coordinate system

In geometry, a coordinate system is a system which uses one or more numbers, or coordinates, to uniquely determine the position of the points or other geometric elements on a manifold such as Euclidean space.

No description.

## DUT1

The time correction DUT1 (sometimes also written DUT) is the difference between Universal Time (UT1), which is defined by Earth's rotation, and Coordinated Universal Time (UTC), which is defined by a network of precision atomic clocks.

## Earth

Earth is the third planet from the Sun and the only astronomical object known to harbor life.

## Epoch (astronomy)

In astronomy, an epoch is a moment in time used as a reference point for some time-varying astronomical quantity, such as the celestial coordinates or elliptical orbital elements of a celestial body, because these are subject to perturbations and vary with time.

## Geodetic astronomy

Geodetic astronomy or astro-geodesy is the application of astronomical methods into networks and technical projects of geodesy.

## Heidelberg

Heidelberg is a college town in Baden-Württemberg situated on the river Neckar in south-west Germany.

## Inertial frame of reference

An inertial frame of reference in classical physics and special relativity is a frame of reference in which a body with zero net force acting upon it is not accelerating; that is, such a body is at rest or it is moving at a constant speed in a straight line.

## Internet

The Internet is the global system of interconnected computer networks that use the Internet protocol suite (TCP/IP) to link devices worldwide.

## Light-time correction

Light-time correction is a displacement in the apparent position of a celestial object from its true position (or geometric position) caused by the object's motion during the time it takes its light to reach an observer.

## Meridian circle

The meridian circle is an instrument for timing of the passage of stars across the local meridian, an event known as a culmination, while at the same time measuring their angular distance from the nadir.

Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.

## Nutation

Nutation (from Latin nūtātiō, "nodding, swaying") is a rocking, swaying, or nodding motion in the axis of rotation of a largely axially symmetric object, such as a gyroscope, planet, or bullet in flight, or as an intended behavior of a mechanism.

## Parallax

Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines.

## Physical body

In physics, a physical body or physical object (or simply a body or object) is an identifiable collection of matter, which may be constrained by an identifiable boundary, and may move as a unit by translation or rotation, in 3-dimensional space.

## Planet

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals.

## Polar motion

Polar motion of the Earth is the motion of the Earth's rotational axis relative to its crust.

## Proper motion

Proper motion is the astronomical measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars.

## Rotation

A rotation is a circular movement of an object around a center (or point) of rotation.

## Rotation around a fixed axis

Rotation around a fixed axis or about a fixed axis of revolution or motion with respect to a fixed axis of rotation is a special case of rotational motion.

## Solar System

The Solar SystemCapitalization of the name varies.

## Solar time

Solar time is a calculation of the passage of time based on the position of the Sun in the sky.

## Star

A star is type of astronomical object consisting of a luminous spheroid of plasma held together by its own gravity.

## Star position

Star position in the sky is defined by a pair of angles relative to the celestial equator: declination (δ) and right ascension (α).

## Sun

The Sun is the star at the center of the Solar System.

## Velocity

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time.

## Year

A year is the orbital period of the Earth moving in its orbit around the Sun.

## Yearbook

A yearbook, also known as an annual, is a type of a book published annually to record, highlight, and commemorate the past year of a school.

## Zenith camera

A zenith camera is an astrogeodetic telescope used today primarily for the local surveys of Earth's gravity field.

## References

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