Epoch J2000 Equinox J2000
|Right ascension||07h 20m 07.37978s|
|Declination||+21° 58′ 56.3377″|
|Apparent magnitude (V)||+3.53|
|Spectral type||F0 IV|
|U−B color index||+0.04|
|B−V color index||+0.34|
|Radial velocity (Rv)||+4.1 km/s|
|Proper motion (μ)||RA: –15.13 mas/yr
Dec.: –9.79 mas/yr
|Parallax (π)||53.94 ± 0.66 mas|
|Distance||60.5 ± 0.7 ly
(18.5 ± 0.2 pc)
|Metallicity [Fe/H]||–0.26 dex|
|Rotational velocity (v sin i)||129.7 km/s|
It has an apparent visual magnitude of +3.53, allowing it to be seen with the naked eye. Wasat is only two-tenths of a degree south of the ecliptic, and therefore is occasionally occulted by the Moon and, more rarely, by a planet. The last occultation by a planet was by Saturn on June 30, 1857, and the next will be by Venus on August 12, 2420. In 1930, the dwarf planet Pluto was discovered about 0.5° to the east of this star by American astronomer Clyde Tombaugh.
In Chinese, 天樽 (Tiān Zūn), meaning Celestial Wine Cup, refers to an asterism consisting of δ Geminorum, 57 Geminorum and ω Geminorum. Consequently, δ Geminorum itself is known as 天樽二 (Tiān Zūn èr, English: the Second Star of Celestial Wine Cup.). From this Chinese name, the name Ta Tsun has appeared.
Delta Geminorum is a subgiant star with the stellar classification F0 IV. It is about 60.5 light-years (18.5 parsecs) distant. This star has 1.57 times the mass of the Sun and is rotating rapidly with a projected rotational velocity of 129.7 km s−1. The estimated age is 1.6 billion years.
Wasat is a member of a triple star system. The inner components form a spectroscopic binary with a period of 6.1 years (2,238.7 days) and an orbital eccentricity of 0.3530. A cooler class K companion is not apparent to the naked eye but clearly visible in a small telescope. It orbits the inner pair with a period of 1,200 years and an eccentricity of 0.11. Although according to  its radial velocity is away from the Sun, it is actually approaching the Solar System. In about 1.1 million years, it will make its closest approach at a separation of roughly 6.7 ly (2.1 pc).
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The name is a mess, "Wasat" meaning "middle" in Arabic, but the middle of WHAT is not clear, whether the middle of Gemini, of the sky, or of the neighboring constellation Orion (which the Arabs referred to as the "Central One"), the star name improperly applied to our Delta.
- Allen, Richard (1889). "The history of the star: Wasat, from p.234 of Star Names, Richard Hinckley Allen, 1889.". Constellations of Words website. Retrieved July 29, 2014.
Wasat and Wesat are from Al Wasat, the Middle, i.e. of the constellation; but some have referred this to the position of the star very near to the ecliptic, the central circle.
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