Castor is the second-brightest object in the zodiac constellation of Gemini. It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem. With an apparent visual magnitude of 1.93, it is one of the brightest stars in the night sky. Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs. Although it is the 'α' (alpha) member of the constellation, it is fainter than 'β' (beta) Geminorum, Pollux.
Zeta Geminorum is a bright star with cluster components, distant optical components and a likely spectroscopic partner in the zodiac constellation of Gemini — in its south, on the left 'leg' of the twin Pollux. It is a classical Cepheid variable star, of which over 800 have been found in our galaxy. As such its regular pulsation and luminosity and its relative proximity means the star is a useful calibrator in computing the cosmic distance ladder. Based on parallax measurements, it is approximately 1,200 light-years from the Sun.
9 Aurigae is a star system in Auriga (constellation). It has an apparent magnitude of about 5, making it visible to the naked eye in many suburban skies. Parallax estimates made by the Hipparcos spacecraft put it at about 86 light-years from the solar system, although individual Gaia Data Release 3 parallaxes place all three components at 88 light years.
24 Cancri is a triple star system in the constellation Cancer. The system is located about 226 light-years away, based on its parallax. The system has a combined apparent magnitude of 6.5, and the two components A and B are separated by 5.7″.
5 Tauri is a binary star in the zodiac constellation of Taurus, located approximately 530 light years from the Sun. It is visible to the naked eye as a faint orange-hued star with an apparent visual magnitude of +4.14. It is moving further from the Earth with a heliocentric radial velocity of +14 km/s.
HD 225218 is a quadruple star system in the northern constellation of Andromeda. The primary component, HD 225218 A, is a giant star with a stellar classification of B9III, an apparent magnitude of 6.16, and is a candidate Lambda Boötis star. It has a fainter, magnitude 9.65 companion, HD 225218 B, at an angular separation of 5.2″ along a position angle of 171°. The primary itself has been identified as a binary star system through interferometry, with the two components separated by 0.165″. The pair, HD 225218 Aa and Ab, orbit each other with a period of about 70 years and an eccentricity of 0.515. Component B is likewise a spectroscopic binary.
HD 44780 is a binary star system in the northern constellation of Gemini, located about 3° north of Mu Geminorum. The pair have a combined apparent visual magnitude of 6.35, which is near the lower limit of visibility to the naked eye. Although it is above magnitude 6.5, it was not included in the Bright Star Catalogue; the designation HD 44780 comes from the Henry Draper catalogue. Based upon parallax measurements, the system is located at a distance of approximately 960 light years from the Sun. It is drifting further away with a radial velocity of +17 km/s.
HR 7578 is a binary star in the constellation of Sagittarius. Their combined apparent magnitude is 6.18. Parallax measurements by the Gaia spacecraft put the system at 46.01 light-years away, making this a nearby system.
ζ Coronae Borealis, Latinised as Zeta Coronae Borealis, is the Bayer designation of a double star in the constellation Corona Borealis. The two components are separated by six arc-seconds and share the same Hipparcos catalogue number and Flamsteed designation. Each of the two is also a spectroscopic multiple system, with a total of five stars in the group.
39 Draconis is a wide binary star system in the northern circumpolar constellation of Draco. It has the Bayer designation b Draconis, while 39 Draconis is the Flamsteed designation. This system is visible to the naked eye as a dim, white-hued point of light with an apparent visual magnitude of 5.0. Parallax measurements made by the Hipparcos spacecraft put it at a distance of 184 light-years, or 56 parsecs away from the Sun. The system is moving closer to the Earth with a heliocentric radial velocity of -24.5 km/s.
Rho Geminorum is a star system that lies 59 light-years away in the constellation of Gemini, about 5 arcminutes east of Castor. The system consists of a primary bright enough to be seen with the naked eye, a faint secondary which has rarely been observed even professionally, and a distant, somewhat bright tertiary which requires telescopic equipment for observation.
Sigma Geminorum is a binary star system in the constellation Gemini, just to the northeast of Pollux. It is visible to the naked eye with an apparent visual magnitude of 4.20. Its annual parallax shift of 26.08 mas indicates that it is located 125 light years from the Sun.
38 Geminorum is a binary star system in the northern zodiac constellation of Gemini. It has the Bayer designation e Geminorum, while 38 Geminorum is the Flamsteed designation. This system is visible to the naked eye as a faint, white-hued point of light with an apparent visual magnitude of 4.71. The primary component is a magnitude 4.75 star, while the secondary is magnitude 7.80. The system is located about 98 light years away from the Sun based on parallax, and is drifting further away with a radial velocity of +16 km/s. It is a potential member of the Tucana–Horologium stellar kinematic group.
81 Geminorum is a binary star system in the northern constellation of Gemini. It has the Bayer designation g Geminorum, while 81 Geminorum is its Flamsteed designation. This system is visible to the naked eye as a faint, orange-hued point of light with an apparent visual magnitude of 4.89. The pair are located approximately 360 light years away from the Sun, based on parallax, and are moving further away with a radial velocity of +83 km/s, having come to within an estimated 164 light-years of the Earth nearly a million years ago. 81 Geminorum lies close enough to the ecliptic to undergo lunar occultations.
ξ Pavonis, Latinised as Xi Pavonis, is a triple star system in the southern constellation of Pavo. It is visible to the naked eye as a faint star with a combined apparent visual magnitude of 4.35 The system is located approximately 440 light-years from the Sun based on parallax, and it is drifting further away with a radial velocity of +12 km/s.
QZ Puppis is a class B2.5V star in the constellation Puppis. Its apparent magnitude is 4.5 and it is approximately 650 light years away based on parallax.
43 Persei is a binary star system in the northern constellation Perseus. It is visible to the naked eye as a dim, yellow-white hued star with an apparent visual magnitude of 5.28. The system is located around 38.5 parsecs (125.4 ly) distant from the Sun, based on parallax.
31 Cygni, also known as ο1 Cygni, Omicron1 Cygni, or V695 Cygni, is a triple star system about 750 light years away in the constellation Cygnus.
16 Serpentis is a binary star system in the Serpens Caput portion of the equatorial constellation of Serpens, located 228 light years from the Sun. It is visible to the naked eye as a fain, orange-hued star with an apparent visual magnitude of 5.261. The system is moving further from the Earth with a heliocentric radial velocity of +3 km/s.
3 Geminorum is a blue supergiant star in the constellation Gemini. It is a small amplitude pulsating variable and a close double star, with a mean combined apparent visual magnitude of about 5.7.
