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.