An Etymological Dictionary of Astronomy and Astrophysics

The brightest star in the constellation → Hercules. It is a → red supergiant of type M5 (surface temperature about 3300 K) lying at a distance of 380 light-years. Rasalgethi is a variable star with a mean magnitude of V = 3.48. It has a fifth magnitude companion 5’’ away. This secondary is itself a double that consists of a 4 solar-mass class G5 giant star with a temperature about that of the Sun and a 2.5 solar-mass F2 dwarf star (somewhat hotter than the Sun) in orbit around each other separated by 0.4 AU with a 52 day period.

See also: Rasalgethi, from Ar. Ra’s al-Jathi (رأس‌الجاثی) “the Kneeler’s Head,” in reference to an early name for the constellation, the figure of the man seen upside down, his head toward the south, from ra’s “head” + jathi “kneeling.”