Mizar

The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.
The multiple star system of Mizar (the double star on the right) and Alcor (left). The unrelated, fainter star Sidus Ludovicianum can be seen lower down.
Radial velocity curves for the two almost identical components

Second-magnitude star in the handle of the Big Dipper asterism in the constellation of Ursa Major.

- Mizar
The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.

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Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.

Double star

Pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.

Pair of stars that appear close to each other as viewed from Earth, especially with the aid of optical telescopes.

Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.
Artist's impression of the discs around the young stars HK Tauri A and B.

Mizar, in Ursa Major, was observed to be double by Benedetto Castelli and Galileo.

Binary system of two stars

Binary star

System of two stars that are gravitationally bound to and in orbit around each other.

System of two stars that are gravitationally bound to and in orbit around each other.

Binary system of two stars
Edge-on disc of gas and dust present around the binary star system HD 106906
Algol B orbits Algol A. This animation was assembled from 55 images of the CHARA interferometer in the near-infrared H-band, sorted according to orbital phase.
Artist's conception of a cataclysmic variable system
Artist's impression of the binary star system AR Scorpii
Artist rendering of plasma ejections from V Hydrae
Artist's impression of the sight from a (hypothetical) moon of planet HD 188753 Ab (upper left), which orbits a triple star system. The brightest companion is just below the horizon.
Schematic of a binary star system with one planet on an S-type orbit and one on a P-type orbit
The two visibly distinguishable components of Albireo
Luhman 16, the third closest star system, contains two brown dwarfs.
Planet Lost in the Glare of Binary Stars (illustration)

Early examples include Mizar and Acrux.

The constellation Ursa Major as it can be seen by the unaided eye.

Ursa Major

Constellation in the northern sky, whose associated mythology likely dates back into prehistory.

Constellation in the northern sky, whose associated mythology likely dates back into prehistory.

The constellation Ursa Major as it can be seen by the unaided eye.
Ursa Major and Ursa Minor in relation to Polaris
Ursa Major shown on a carved stone, c.1700, Crail, Fife
H. A. Rey's alternative asterism for Ursa Major can be said to give it the longer head and neck of a polar bear, as seen in this photo, from the left side.
Ursa Major as depicted in Urania's Mirror, a set of constellation cards published in London c.1825.
Johannes Hevelius drew Ursa Major as if being viewed from outside the celestial sphere.
Starry Night Over the Rhone by Vincent van Gogh (1888)
Polaris and the Big Dipper on the flag of Alaska.

ζ Ursae Majoris, Mizar, the second star in from the end of the handle of the Big Dipper, and the constellation's fourth-brightest star. Mizar, which means "girdle," forms a famous double star, with its optical companion Alcor (80 Ursae Majoris), the two of which were termed the "horse and rider" by the Arabs.

The asterism of the Big Dipper (shown in this star map in green) lies within the constellation of Ursa Major.

Big Dipper

Large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude.

Large asterism consisting of seven bright stars of the constellation Ursa Major; six of them are of second magnitude and one, Megrez (δ), of third magnitude.

The asterism of the Big Dipper (shown in this star map in green) lies within the constellation of Ursa Major.
The Big Dipper seen from Fujian
The Hall of the Big Dipper in a Taoist temple, Wuhan
The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.
The Big Dipper (Ursa Major) photographed by Prof. Chen Hualin in Dakawa, Morogoro, Tanzania at midnight on February 16, 2018
4D proper moving in -/+ 150 000 years.
Guide to using Big Dipper to locate Arcturus, Spica, and Polaris
The "Starry Plough", used by Irish nationalists and leftists

In the same line of sight as Mizar, but about one light-year beyond it, is the star Alcor (80 UMa).

Star system named DI Cha. While only two stars are apparent, it is actually a quadruple system containing two sets of binary stars.

Star system

Small number of stars that orbit each other, bound by gravitational attraction.

Small number of stars that orbit each other, bound by gravitational attraction.

Star system named DI Cha. While only two stars are apparent, it is actually a quadruple system containing two sets of binary stars.
Orbits of the HR 6819 hierarchical triple star system: an inner binary with one star (orbit in blue) and a black hole (orbit in red), encircled by another star in a wider orbit (also in blue).
Subsystem notation in Tokovinin's Multiple Star Catalogue
Sirius A (center), with its white dwarf companion, Sirius B (lower left) taken by the Hubble Space Telescope.
HD 98800 is a quadruple star system located in the TW Hydrae association.

Mizar is often said to have been the first binary star discovered when it was observed in 1650 by Giovanni Battista Riccioli, p. 1 but it was probably observed earlier, by Benedetto Castelli and Galileo. Later, spectroscopy of its components Mizar A and B revealed that they are both binary stars themselves.

Giovanni Battista Riccioli

Italian astronomer and a Catholic priest in the Jesuit order.

Italian astronomer and a Catholic priest in the Jesuit order.

Riccioli as portrayed in the 1742 Atlas Coelestis (plate 3) of Johann Gabriel Doppelmayer.
The crescent phases of Venus and detailed representations of its appearance as seen through a telescope, from Riccioli's 1651 New Almagest.
Map of the Moon from the New Almagest.
Frontispiece of Riccioli's 1651 New Almagest. Mythological figures observe the heavens with a telescope and weigh the heliocentric theory of Copernicus in a balance against his modified version of Tycho Brahe's geo-heliocentric system, in which the Sun, Moon, Jupiter, and Saturn orbit the Earth while Mercury, Venus, and Mars orbit the Sun. The old Ptolemaic geocentric theory lies discarded on the ground, made obsolete by the telescope's discoveries. These are illustrated at top and include phases of Venus and Mercury and a surface feature on Mars (left), moons of Jupiter, rings of Saturn, and features on the Moon (right). The balance tips in favor of Riccioli's "Tychonic" system.
Illustration from Riccioli's 1651 New Almagest showing the effect a rotating Earth should have on projectiles. When the cannon is fired at eastern target B, cannon and target both travel east at the same speed while the ball is in flight. The ball strikes the target just as it would if the Earth were immobile. When the cannon is fired at northern target E, the target moves more slowly to the east than the cannon and the airborne ball, because the ground moves more slowly at more northern latitudes (the ground hardly moves at all near the pole). Thus the ball follows a curved path over the ground, not a diagonal, and strikes to the east, or right, of the target at G.
Representations from Riccioli's 1665 Reformed Astronomy of Saturn's changing appearance.
Geographicae crucis fabrica et usus ad repraesentandam mira facilitate omnem dierum noctiumque ortuum solis et occasum, horarumque omnium varietatem, 1643

He is often credited with being one of the first to telescopically observe the star Mizar and note that it was a double star; however, Castelli and Galileo observed it much earlier.

Mizar and Alcor in constellation Ursa Major

Mizar and Alcor

Mizar and Alcor are two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in the constellation of Ursa Major.

Mizar and Alcor are two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in the constellation of Ursa Major.

Mizar and Alcor in constellation Ursa Major

Mizar is the second star from the end of the Big Dipper's handle, and Alcor its fainter companion.

1636 portrait by Justus Sustermans

Galileo Galilei

Italian astronomer, physicist and engineer, sometimes described as a polymath, from the city of Pisa, then part of the Duchy of Florence.

Italian astronomer, physicist and engineer, sometimes described as a polymath, from the city of Pisa, then part of the Duchy of Florence.

1636 portrait by Justus Sustermans
Galileo's elder daughter Virginia was particularly devoted to her father
Galileo's "cannocchiali" telescopes at the Museo Galileo, Florence
An illustration of the Moon from Sidereus Nuncius, published in Venice, 1610
It was on this page that Galileo first noted an observation of the moons of Jupiter. This observation upset the notion that all celestial bodies must revolve around the Earth. Galileo published a full description in Sidereus Nuncius in March 1610
The phases of Venus, observed by Galileo in 1610
Galileo Galilei, portrait by Domenico Tintoretto
Cristiano Banti's 1857 painting Galileo facing the Roman Inquisition
Portrait of Galileo Galilei by Justus Sustermans, 1636. Uffizi Museum, Florence.
Portrait, originally attributed to Murillo, of Galileo gazing at the words "E pur si muove" (And yet it moves) (not legible in this image) scratched on the wall of his prison cell. The attribution and narrative surrounding the painting have since been contested.
Tomb of Galileo, Santa Croce, Florence
Middle finger of Galileo's right hand
A replica of the earliest surviving telescope attributed to Galileo Galilei, on display at the Griffith Observatory
Galileo's geometrical and military compass, thought to have been made c. 1604 by his personal instrument-maker Marc'Antonio Mazzoleni
The earliest known pendulum clock design. Conceived by Galileo Galilei
Galileo e Viviani, 1892, Tito Lessi
Dome of the Cathedral of Pisa with the "lamp of Galileo"
Galileo showing the Doge of Venice how to use the telescope (fresco by Giuseppe Bertini)
Statue outside the Uffizi, Florence
Statue of Galileo by Pio Fedi (1815–1892) inside the Lanyon Building of the Queen's University of Belfast. Sir William Whitla (Professor of Materia Medica 1890–1919) brought the statue back from Italy and donated it to the university.

He observed the double star Mizar in Ursa Major in 1617.

Mizar and Alcor in constellation Ursa Major

Alcor (star)

Binary star system in the constellation of Ursa Major.

Binary star system in the constellation of Ursa Major.

Mizar and Alcor in constellation Ursa Major
The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.

It is the fainter companion of Mizar, the two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in Ursa Major.

Fuxing, Luxing, and Shouxing at a Benzhu temple at the Jinsuo Island in Dali, Yunnan.

Sanxing (deities)

The Sanxing are the gods of the three stars or constellations considered essential in Chinese astrology and mythology: Jupiter, Ursa Major, and Sirius.

The Sanxing are the gods of the three stars or constellations considered essential in Chinese astrology and mythology: Jupiter, Ursa Major, and Sirius.

Fuxing, Luxing, and Shouxing at a Benzhu temple at the Jinsuo Island in Dali, Yunnan.
The Roof Decoration of Sanxing. 
At Magong Beiji Temple, Taiwan

The star of Lu (祿), Luxing 祿星, is Mizar (ζ Ursa Majoris), or, in traditional Chinese astronomy, the sixth star in the Wenchang cluster, and like the Fu star came to be personified.