Zeta Aquarii, at the center of Aquarius's Water Jar or Urn, almost exactly rides the celestial equator. Until 2003, the star was located in the southern celestial hemisphere. However, precession - the 26,000-year wobble in the Earth's axis - brings it north at a rate of 0.3' per year. Around November 21, 2003, it crossed the equator into the northern hemisphere.
Components and Properties
Physically, ζ Aqr is a fine double star 103 light years away; its components shine together at magnitude 3.7. Their current separation of only 1.7" make them a fine sight in the telescope, but also render their individual characteristics difficult to measure. The eastern star, ζ2 Aqr, is slightly the brighter at magnitude 4.36, and thus the primary. ζ1 Aqr comes in just a bit fainter, at magnitude 4.57. Both are class hydrogen-fusing main-sequence stars: ζ2 of class F3, and ζ1 is class F2.
The result is a pair of white jewels that in the nineteenth century were called "white and very white." Temperatures of about 7000 K ensure that nearly all the stars' radiation falls in the optical spectrum. ζ1 is 12 times more luminous than the Sun; ζ2 is 15 times more luminous. From this, we deduce masses of 1.8 times the Sun's, with ζ2 just a bit more massive. They orbit each other with an uncertain period of 760 years at an average separation of 140 AU, with a crudely-known eccentricity that takes them from 95 AU to 210 AU apart. The orbit gives a total system mass of 5 times the Sun's, versus 3.6 as derived from luminosity and temperature. This clearly shows the orbital parameters to be somewhat in error.
From each star, the other would shine with the light of 70 full Moons, on average.
[Adapted from STARS by Jim Kaler, Professor Emeritus of Astronomy, University of Illinois]