Properties
Christian Mayer, director of the Mannheim Observatory, is considered the first to have observed Zeta Aquarii to be double, in 1777. A couple of years later, William Herschel also discovered this duality. The two stars have an orbital period of about 587 years. The semimajor axis is 3.8 arcseconds and they have an orbital eccentricity of 0.40. The orbital plane is inclined by 138.2° to the line of sight.
The brighter component, ζ Aquarii A, is a yellow-white-hued F-type main sequence star with an apparent magnitude of +4.42. Its companion, ζ Aquarii B, is a yellow-white-hued F-type subgiant with an apparent magnitude of +4.51. The fact that their brightness is so similar makes the pair easy to measure and resolve.
ζ Aquarii B is a suspected astrometric binary system with a 25.8 year orbital period and a semimajor axis of 10.8 astronomical units. If this is confirmed, then the smaller companion may be a red dwarf with a classification of M0 V and 40% of the Sun's mass.
Zeta Aquarii is currently a northern hemisphere object. In 2004 it was directly above the celestial equator, and before that it was located south of it.
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