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HEZE (Zeta Virginis). Almost due north ofSpica inVirgo,Heze forms a nice right triangle withPorrima, which lies just to the west of it. While the meanings of the names of the other stars are well known,that of "Heze" is not, and the star usually just goes by itsGreek letter name of Zeta Vir. Physically, this third magnitude (3.37) white class A (A3)hydrogen-fusing dwarf is not terribly imposing. With a temperatureof 8400 Kelvin, it shines with the light of 18Suns from a distance of 73 light years. Temperature and luminosity together with the theory of stellarstructure and evolution give a mass of 1.9 times that of the Sun,a radius of twice solar, and an age of roughly half a billionyears. A number of class A stars have surrounding dusty disks thatimply the possibility of planetary systems, but not this one. Itsmost significant physical aspect may be its high equatorialrotation speed of at least 222 kilometers per second, which givesa rotation period of under half a day. There is some evidence forelevated abundances of heavier elements as well, which may be theproduct of diffusion (physical separation), which is odd given ahigh spin rate that tends to cause mixing. Heze's great claim tofame lies in its location as an "equator star," one that falls veryclose to -- and helps us visually locate -- thecelestial equator (like Alpha Sextantisto the east). The star currently lies only a bit over half adegree to the south of that great divide.Precession, the wobble of the Earth'saxis caused by the gravitational action of the Sun and Moon on theEarth's equatorial bulge (caused by its rotation), is movingVirgo's portion of the celestial equator to the north. As aresult, the star appears to be moving slowly (at a rate of 18seconds of arc per year) farther to the south. Not all that longago, however, Heze was NORTH of the equator, the passage into thedomain of the southern hemisphere, where it will stay for the nextseveral thousand years, taking place in February of 1883.
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