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A multiple star system consists of two or more stars that appear from Earth to be close to one another in the sky. [dubious – discuss] This may result from the stars actually being physically close and gravitationally bound to each other, in which case it is a physical multiple star, or this closeness may be merely apparent, in which case it is an optical multiple star [a] Physical multiple ...
The secondary star in a binary star system may be designated as the hot companion or cool companion, depending on its temperature relative to the primary star. Examples: Antares (Alpha Scorpii) is a red supergiant star in a binary system with a hotter blue main-sequence star Antares B. Antares B can therefore be termed a hot companion of the ...
A multi-star system consists of two or more gravitationally bound stars that orbit each other. The simplest and most common multi-star system is a binary star, but systems of three or more stars exist. For reasons of orbital stability, such multi-star systems are often organized into hierarchical sets of binary stars. [116]
The stars with the most confirmed planets are the Sun (the Solar System's star) and Kepler-90, with 8 confirmed planets each, followed by TRAPPIST-1 with 7 planets. The 1007 multiplanetary systems are listed below according to the star's distance from Earth. Proxima Centauri, the closest star to the Solar System, has three planets (b, c and d).
The Harvard system is a one-dimensional classification scheme by astronomer Annie Jump Cannon, who re-ordered and simplified the prior alphabetical system by Draper (see History). Stars are grouped according to their spectral characteristics by single letters of the alphabet, optionally with numeric subdivisions.
For example, Sirius, the brightest star in the sky, is actually a double star, consisting of the naked-eye visible Sirius A and its dim white-dwarf companion Sirius B. The first exoplanet tentatively identified around the second brightest star in the triple star system Alpha Centauri is accordingly called Alpha Centauri Bb.
Alpha Centauri is a triple star system, with its two main stars, A and B, together comprising a binary component. The AB designation, or older A×B , denotes the mass centre of a main binary system relative to companion star(s) in a multiple star system. [ 85 ]
The principal component of the Solar System is the Sun, a G-type main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally. [37] The Sun's four largest orbiting bodies, the giant planets, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%.