TAU AUR (Tau Aurigae). To the west of the "Haedi," the Kids of Auriga (traditionally made of Eta and Zeta Aurigae, to which is usually added more northerly Epsilon), near the western edge of Auriga's classic figure, lies a similar triangle which rather stands out as the fainter "Little Kids," made of Nu, Tau, and Upsilon Aur. The brightest, just northwest of Theta Aur, is fourth magnitude (3.97) Nu. Fifth magnitude (at 4.52, just over the line) Tau lies just to the west of it, while fifth magnitude (4.74) Upsilon, the faintest, falls a bit to the south.
The Little Kids. North is to the left. Theta Aurigae, near bottom center, leads the eye upward to the thin triangle of stars we might call "The Little Kids," made (clockwise from lower left) of Nu, Tau, and Upsilon Aurigae. The figure is remarkably similar (though reversed) to the classic "Kids" near Capella, made of Epsilon, Zeta, and Eta Aurigae.
Oddly, all are giants. Of the three, class G (G8) Tau (probably the least distinguished) is the warmest. At a distance of 213 light years (nominally a hair closer than Nu Aur), like Nu, Tau is a helium-fusing "clump star" (so- called because of the large number of similar stars). With an ill- determined temperature of 4770 Kelvin, Tau radiates 79 solar luminosities into space, which together lead to a radius of 13.0 Suns, a mass of 2.5 times that of the Sun, and an age of 700 million years. Just over 100 million years ago, Tau was a class A hydrogen-fusing dwarf. Direct measure of angular diameter via interferometry (which makes use of the interfering properties of light) yields a satisfyingly similar radius of 13.8 Suns, not all that much for a giant. Accepting the distances of Tau and Nu as correct, the two lie just three light years apart. though they are much too distance from each other to form an actual binary. They are instead moving in opposite directions and are merely passing each other like the classical "ships in the night." From each, the other would present a fine sight. From Nu, Tau would shine at magnitude -4.9, much like Venus at her brightest, though redder. From Tau, Nu would appear even grander, shining another half magnitude brighter.
Written by Jim Kaler 4/04/08. Return to STARS.