Astrometry focuses on measuring the positions and motions of celestial objects, which enables the determination of distances to stars and other astronomical objects.

Spherical coordinates, consisting of right ascension, declination, and distance, are widely used in astrometry to specify the positions of celestial objects.

Parallax is the apparent shift in the position of a star due to the Earth's motion around the Sun. It enables astronomers to measure the distances to nearby stars.

Proper motion refers to the angular velocity of a star across the sky, as observed from Earth. It provides insights into the star's peculiar motion relative to the surrounding stars.

Telescopes, equipped with specialized instruments, are the primary tools used in astrometry to measure the positions and motions of celestial objects.

The Hipparcos mission was a groundbreaking astrometry satellite that precisely measured the positions and distances to nearby stars, revolutionizing our understanding of stellar distances.

Parallax involves measuring the time it takes for light to travel from a star to Earth to determine its distance. This technique is fundamental in astrometry for measuring stellar distances.

In exoplanet detection, astrometry plays a crucial role in measuring the distance to exoplanet host stars, which is essential for determining the physical properties of the exoplanets.

Polaris, also known as the North Star, is commonly used as a reference point for measuring the positions of other objects in astrometry due to its relatively fixed position in the sky.

Nutation refers to the apparent motion of stars caused by the precession of the Earth's axis. It is a small, periodic variation in the position of the celestial poles.

The Gaia spacecraft is a space telescope specifically designed for astrometry. It has provided precise measurements of stellar positions, distances, and motions, revolutionizing our understanding of the Milky Way galaxy.

Diurnal motion refers to the apparent change in the position of a star due to the Earth's rotation. It causes stars to appear to rise in the east and set in the west.

VLBI is a technique that combines signals from multiple radio telescopes to achieve high angular resolution. It is used in astrometry to measure the positions of distant celestial objects with high precision.

The vernal equinox, which marks the beginning of spring in the Northern Hemisphere, serves as the fundamental reference point for defining the celestial coordinate system.

Aberration of light refers to the apparent shift in the position of a star due to the Earth's orbital motion around the Sun. It causes stars to appear slightly displaced from their true positions.