Zeta Aurigae

Zeta Aurigae by Chesley Bonestell

Zeta Aurigae as portrayed by the artist Chesley Bonestell. © Bonestell Space Art, used with permission.

Zeta Aurigae is a famous eclipsing binary in the constellation Auriga and one of the Kids (in Latin "Haedus"). It is also known as Haedus I and by an astonishing coincidence, its constellation mate, Epsilon Aurigae, which is the second Kid ("Haedus II"), is also a well-known (and even more remarkable) eclipsing binary.


Zeta consists an orange supergiant (spectral type K4) in orbit around a blue B star (type B5) with a period of 972.2 days (2.66 years). Because the orientation of the orbit lies within 3° of our line of sight, every 2.66 years the smaller B star hides completely behind the larger K star (which is about as wide as Venus's orbit), and the combined visual light drops by 0.15 magnitude (about 15%). Averaging 4.2 astronomical units (AU) apart, the two go around each other in an elliptical orbit that takes them from 5.9 AU to 2.5 AU apart.


visual magnitude 3.69
absolute magnitude -3.23
spectral type K4II
surface temperature 3,950 K (K star), 15,300 K (B star)
luminosity 4,800 Lsun (K star), 1,000 Lsun (B star)
radius 148 Rsun (K star), 4.5 Rsun (B star)
mass 5.8 Msun (K star), 4.8 Msun (B star)
distance 790 ± 150 light-years (242 ± 47 pc)
position RA 05h 02m 28.7s; Dec +41° 04' 33"
other designations Haedi Haedus, Sadatoni, Saclateni,
8 Aurigae, HR 1612, HD 32068,
BD+40°1142A, FK5 1137,
HIP 23453, SAO 39966, GC 6137,
CCDM 05025+4105