Astrometry

An astrolabe (Greek: ἀστρολάβος astrolabos, "star-taker") is an elaborate inclinometer, historically used by astronomers, navigators, and astrologers.

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

In astronomy and navigation, the celestial sphere is an imaginary sphere of arbitrarily large radius, concentric with Earth.

A Cepheid variable (/ˈsɛfiːɪd/ or /ˈsiːfiːɪd/) is a type of star that pulsates radially, varying in both diameter and temperature and producing changes in brightness with a well-defined stable period and amplitude.

In physics, a frame of reference (or reference frame) consists of an abstract coordinate system and the set of physical reference points that uniquely fix (locate and orient) the coordinate system and standardize measurements.

Right ascension (abbreviated RA; symbol α) is the angular distance measured eastward along the celestial equator from the vernal equinox to the hour circle of the point in question.

The zodiac is the circle of twelve 30° divisions of celestial longitude employed by western astrology and (formerly) astronomy.

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

Astrophotography is a specialized type of photography for recording images of astronomical objects and large areas of the night sky.

The ecliptic coordinate system is a celestial coordinate system commonly used for representing the positions and orbits of Solar System objects.

In astronomy and celestial navigation, an ephemeris (plural: ephemerides; from Latin ephemeris, "diary", from Greek: ἐφημερίς, ephēmeris, "diary, journal") gives the positions of naturally occurring astronomical objects as well as artificial satellites in the sky at a given time or times.

The equatorial coordinate system is a celestial coordinate system widely used to specify the positions of celestial objects.

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.

Proper motion is the astronomical measure of the observed changes in apparent positions of stars in the sky as seen from the center of mass of the Solar System compared to the imaginary fixed background of the more distant stars.

The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point.

Theoretical astronomy is the use of the analytical models of physics and chemistry to describe astronomical objects and astronomical phenomena.

The cosmolabe was an ancient astronomical instrument resembling the astrolabe, formerly used for measuring the angles between heavenly bodies.