Zet

Its story

Zeta Sagittae is a multiple star in the small constellation of the Arrow, tucked just beneath Cygnus. At its heart sits an inner pair of two nearly identical white stars chasing each other on a strongly elongated 23.2-year orbit, so close together that on instrumental scales they are barely a hand-span apart. Sagitta is one of the tiniest figures in the sky, yet also among the oldest: it already appears in Ptolemy's catalogues in the second century.