  The red giant ${\delta}$ Muscae is known since 1919 to be a spectroscopic
binary, and the first and only orbit was determined in 1936, claiming the
period to be 847 days. This was discrepant with the Hipparcos determined
astrometric orbit. Using the latest data available for this object - leading to
a 100 yr time-span - we show here that the correct period is 423 d, and are
able for the first time to combine the spectroscopic orbit with the Hipparcos
orbit. Using all the available information, we find that the $\sim$ 1.2 solar
mass red giant must have a $\sim$ 0.3 - 0.4 solar mass M dwarf companion, and
that the system will soon evolve towards a He WD binary system. Given its
relatively short period, ${\delta}$ Muscae may be an ideal benchmark for
testing astrometric orbits obtained by Gaia for very bright stars.
