Thanks to James B. Kaler. These contents are the property of the author and are reproduced from original without the author's express consent because of fair use and valid educational purposes.
With a name that does not ring much of a bell among astronomers, and shining only at the bright end of fourth magnitude, neither does the star itself. Seventh brightest in the constellation Gemini, Bayer still gave it the Delta designation, the star beaten out by Pollux (Beta), Castor (Alpha), Alhena (Gamma), Epsilon,Eta, and Mu. Yet it is not without glory. 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. Wasat serves as a "marker" star like Polaris and Mintaka (which reveal the celestial pole and equator). Wasat leads our eye to the ECLIPTIC, the apparent path the Sun seems to take around us as we orbit. Only two-tenths of a degree south of the ecliptic, it is but half the angle of the first magnitude ecliptic marker Regulus. A line drawn from Wasat through Regulus nicely defines the solar path. Halfway between lies the "Beehive" star cluster in Cancer. Better, Wasat marks the famed and last planet Pluto, as Clyde Tombaugh discovered the body close to the star in 1930. Taking 248 years to orbit the Sun, in the past 66 years Pluto has moved only into Ophiuchus 16 degrees north of Antares in Scorpius. The whole observed 70-year path can be taken in one glance after Antares rises. Since the ecliptic passes only 5 degrees north of Antares, we also see that Pluto is now far (over 10 degrees) above the plane of the Solar System, testimony to its strangely tilted orbit, Wasat closely marking the place where Pluto crosses the ecliptic on its way north. The star is also somewhat more solar than most of its naked-eye brethren, a class F "subgiant" with a temperature of 6700 Kelvin, only 1000 Kelvin hotter than the Sun, its distance of 59 light years telling that it shines with just 10 times the solar luminosity. Subgiants are stars that are in the first stages of expanding to gianthood after the central nuclear fire goes out, so Wasat is now beginning to expire. It will soon be a "gap" star like Caph (Beta Cassiopeiae). Tucked next to it is a cooler ordinary class K companion, easily seen through a small telescope, that is 1200 Kelvin cooler than the Sun. Over 100 times the Earth-Sun distance from Wasat proper, the companion takes 1200 years to orbit. Wasat itself may be a close inseparable double, though no one is sure. Keep your eye on this star: Pluto will pass it again in just 179 years.