Proper motion in the context of "Hipparcos Catalogue"

In astronomy, the fixed stars (Latin: stellae fixae) are the luminary points, mainly stars, that appear not to move relative to one another against the darkness of the night sky in the background. This is in contrast to those lights visible to the naked eye, namely the planets and comets, which appear to move slowly among those "fixed" stars. The fixed stars include all the stars visible to the naked eye other than the Sun, as well as the faint band of the Milky Way. Due to their star-like appearance when viewed with the naked eye, the few visible individual nebulae and other deep-sky objects are also counted among the fixed stars. Approximately 6,000 stars are visible to the naked eye under optimal conditions.

The term fixed stars is a misnomer because those celestial objects are not actually fixed with respect to one another or to Earth. Due to their immense distance from Earth, these objects appear to move so slowly in the sky that the change in their relative positions is nearly imperceptible on human timescales, except under careful examination with modern instruments, such as telescopes, that can reveal their proper motions. Hence, they can be considered to be "fixed" for many purposes, such as navigation, charting of stars, astrometry, and timekeeping.

The north and south celestial poles are the two points in the sky where Earth's axis of rotation, indefinitely extended, intersects the celestial sphere. The north and south celestial poles appear permanently directly overhead to observers at Earth's North Pole and South Pole, respectively. As Earth spins on its axis, the two celestial poles remain fixed in the sky, and all other celestial points appear to rotate around them, completing one circuit per day (strictly, per sidereal day).

The celestial poles are also the poles of the celestial equatorial coordinate system, meaning they have declinations of +90 degrees and −90 degrees (for the north and south celestial poles, respectively). Despite their apparently fixed positions, the celestial poles in the long term do not actually remain permanently fixed against the background of the stars. Because of a phenomenon known as the precession of the equinoxes, the poles trace out circles on the celestial sphere, with a period of about 25,700 years. The Earth's axis is also subject to other complex motions which cause the celestial poles to shift slightly over cycles of varying lengths (see nutation, polar motion and axial tilt). Finally, over very long periods the positions of the stars themselves change, because of the stars' proper motions. To take into account such movement, celestial pole definitions come with an epoch to specify the date of the rotation axis; J2000.0 is the current standard.

In astronomy, superluminal motion is the apparently faster-than-light motion seen in some radio galaxies, BL Lac objects, quasars, blazars and recently also in some galactic sources called microquasars. Bursts of energy moving out along the relativistic jets emitted from these objects can have a proper motion that appears greater than the speed of light. All of these sources are thought to contain a black hole, responsible for the ejection of mass at high velocities. Light echoes can also produce apparent superluminal motion.

Sunspots are temporary spots on the Sun's surface that are darker than the surrounding area. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sunspots appear within active regions, usually in pairs of opposite magnetic polarity. Their number varies according to the approximately 11-year solar cycle.

Individual sunspots or groups of sunspots may last anywhere from a few days to a few months, but eventually decay. Sunspots expand and contract as they move across the surface of the Sun, with diameters ranging from 16 km (10 mi) to 160,000 km (100,000 mi). Larger sunspots can be visible from Earth without the aid of a telescope. They may travel at relative speeds, or proper motions, of a few hundred meters per second when they first emerge.

In astronomy, an equinox is either of two places on the celestial sphere at which the ecliptic intersects the celestial equator. Although there are two such intersections, the equinox associated with the Sun's ascending node is used as the conventional origin of celestial coordinate systems and referred to simply as "the equinox". In contrast to the common usage of spring/vernal and autumnal equinoxes, the celestial coordinate system equinox is a direction in space rather than a moment in time.

In a cycle of about 25,800 years, the equinox moves westward with respect to the celestial sphere because of perturbing forces; therefore, in order to define a coordinate system, it is necessary to specify the date for which the equinox is chosen. This date should not be confused with the epoch. Astronomical objects show real movements such as orbital and proper motions, and the epoch defines the date for which the position of an object applies. Therefore, a complete specification of the coordinates for an astronomical object requires both the date of the equinox and of the epoch.

Hipparcos was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions and distances of celestial objects on the sky. This was the first practical attempt at all-sky absolute parallax measurement, something not possible with groundside observatories, and thus represented a fundamental breakthrough in astronomy. The resulting high-precision measurements of the absolute positions, proper motions, and parallaxes of stars enabled better calculations of their distance and tangential velocity; when combined with radial velocity measurements from spectroscopy, astrophysicists were able to finally measure all six quantities needed to determine the motion of stars. The resulting Hipparcos Catalogue, a high-precision catalogue of more than 118,200 stars, was published in 1997. The lower-precision Tycho Catalogue of more than a million stars was published at the same time, while the enhanced Tycho-2 Catalogue of 2.5 million stars was published in 2000. Hipparcos's follow-up mission, Gaia, was launched in 2013.

The word "Hipparcos" is an acronym for High Precision Parallax Collecting Satellite and also a reference to the ancient Greek astronomer Hipparchus of Nicaea, who is noted for applications of trigonometry to astronomy and his discovery of the precession of the equinoxes.

61 Cygni /ˈsɪɡni/ is a binary star system in the northern constellation Cygnus, consisting of a pair of K-type dwarf stars that orbit each other in a period of about 659 years. Of apparent magnitude 5.20 and 6.05, respectively, they can be seen with binoculars in city skies or with the naked eye in rural areas without light pollution.

61 Cygni first attracted the attention of astronomers when its large proper motion was first demonstrated by Giuseppe Piazzi in 1804. In 1838, Friedrich Bessel measured its distance from Earth at about 10.4 light-years, very close to the actual value of about 11.4 light-years; this was the first distance estimate for any star other than the Sun, and the first star to have its stellar parallax measured. Among all stars or stellar systems listed in the latest Gaia catalogues, 61 Cygni has the sixth-highest proper motion, and the highest among all naked-eye visible stars.

In astronomy, stellar kinematics is the observational study or measurement of the kinematics or motions of stars through space.

Stellar kinematics encompasses the measurement of stellar velocities in the Milky Way and its satellites as well as the internal kinematics of more distant galaxies. Measurement of the kinematics of stars in different subcomponents of the Milky Way including the thin disk, the thick disk, the bulge, and the stellar halo provides important information about the formation and evolutionary history of our Galaxy. Kinematic measurements can also identify exotic phenomena such as hypervelocity stars escaping from the Milky Way, which are interpreted as the result of gravitational encounters of binary stars with the supermassive black hole at the Galactic Center.

Time-domain astronomy is the study of how astronomical objects change with time. Said to have begun with Galileo's Letters on Sunspots, the field has now naturally expanded to encompass variable objects beyond the Solar System. Temporal variation may originate from movement of the source, or changes in the object itself. Common targets include novae, supernovae, pulsating stars, flare stars, blazars and active galactic nuclei. Optical time domain surveys include OGLE, HAT-South, PanSTARRS, SkyMapper, ASAS, WASP, CRTS, GOTO, and the LSST at the Vera C. Rubin Observatory.

Time-domain astronomy studies transient astronomical events ("transients"), which include various types of variable stars, including periodic, quasi-periodic, high proper motion stars, and lifecycle events (supernovae, kilonovae) or other changes in behavior or type. Non-stellar transients include asteroids, planetary transits and comets.

Mirach is a prominent star in the northern constellation of Andromeda. It is pronounced /ˈmaɪræk/ and has the Bayer designation Beta Andromedae, which is Latinized from β Andromedae. This star is positioned northeast of the Great Square of Pegasus and is potentially visible to all observers north of latitude 54° S. It is commonly used by stargazers to find the Andromeda Galaxy. The galaxy NGC 404, also known as Mirach's Ghost, is seven arcminutes away from Mirach.

This star has an apparent visual magnitude of around 2.07, varying between 2.01 and 2.10, which at times makes it the brightest star in the constellation. Based upon parallax measurements, it is roughly 197 light-years (60 parsecs) from the Solar System. Its apparent magnitude is reduced by 0.06 by extinction due to gas and dust along the line of sight. The star has a negligible radial velocity of 0.1 km/s, but with a relatively large proper motion, traversing the celestial sphere at an angular rate of 0.208″·yr.

CFBDSIR 2149-0403 (full designation CFBDSIR J214947.2-040308.9) is a free-floating planetary-mass object or possibly a high-metallicity, low-mass brown dwarf in the constellation Aquarius. Originally, it was thought to be part of the AB Doradus moving group (ABDMG) as indicated by its position and proper motion, but the same team that discovered the object and conjectured its membership in the group has now rejected that hypothesis due to newer measurements. Without that membership, the age and mass of the object cannot be constrained.