Astrometry is concerned with accurately determining the positions and motions of celestial objects in the sky.

An astrometer is a specialized instrument designed specifically for measuring the positions of celestial objects.

The equatorial coordinate system is widely used in astrometry to define the positions of celestial objects based on their right ascension and declination.

Proper motion refers to the actual movement of stars in space, distinct from the apparent motion caused by the Earth's precession.

The annual parallax of a star is inversely proportional to its distance from Earth.

Astrometry, specifically through the measurement of stellar parallax, is the primary method used to determine the distances to stars.

Aberration of light is the apparent shift in the position of a star due to the Earth's orbital motion.

Precession of the equinoxes is the gradual shift in the position of the equinoxes along the ecliptic.

The horizontal coordinate system is used to describe the positions of objects near the celestial poles.

Nutation is the small, periodic oscillation of the Earth's axis of rotation.

The equatorial coordinate system is based on the Earth's equator and the celestial poles.

Nutation causes a slight wobble in the Earth's axis of rotation, resulting in a small, periodic movement of stars.

The ecliptic coordinate system is based on the ecliptic, the plane of Earth's orbit around the Sun.

Diurnal motion is the apparent shift in the position of a star due to the Earth's rotation.

The galactic coordinate system is based on the Milky Way galaxy's center and its disk.