Rho-1

Its story

Rho-1 Sagittarii is a white-yellow subgiant pulsing among the arrows of the Archer, some 127 light-years away. It belongs to the family of Delta Scuti variables, stars that tremble on timescales of hours as they seek equilibrium between gravity and internal pressure. At magnitude 3.9 it is plainly visible to the naked eye on a clean night, one of the few Delta Scuti bright enough to need no instrument at all.