HEZE (Zeta Virginis). Almost due north of Spica in Virgo, Heze forms a nice right triangle with Porrima, 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 its Greek letter name of Zeta Vir. Physically, this third magnitude (3.37) white class A (A3) hydrogen-fusing dwarf is not terribly imposing. With a temperature of 8400 Kelvin, it shines with the light of 18 Suns from a distance of 73 light years. Temperature and luminosity together with the theory of stellar structure 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 billion years. A number of class A stars have surrounding dusty disks that imply the possibility of planetary systems, but not this one. Its most significant physical aspect may be its high equatorial rotation speed of at least 222 kilometers per second, which gives a rotation period of under half a day. There is some evidence for elevated abundances of heavier elements as well, which may be the product of diffusion (physical separation), which is odd given a high spin rate that tends to cause mixing. Heze's great claim to fame lies in its location as an "equator star," one that falls very close to -- and helps us visually locate -- the celestial equator (like Alpha Sextantis to the east). The star currently lies only a bit over half a degree to the south of that great divide. Precession, the wobble of the Earth's axis caused by the gravitational action of the Sun and Moon on the Earth's equatorial bulge (caused by its rotation), is moving Virgo's portion of the celestial equator to the north. As a result, the star appears to be moving slowly (at a rate of 18 seconds of arc per year) farther to the south. Not all that long ago, however, Heze was NORTH of the equator, the passage into the domain of the southern hemisphere, where it will stay for the next several thousand years, taking place in February of 1883.
Written by Jim Kaler. Return to STARS.