Del

Its story

δ Coronae Borealis belongs to the small semicircular diadem that traces the Northern Crown. It is a yellow giant 170 light-years away, two and a half solar masses, swollen to seven radii. Every 45 days its brightness shifts sinusoidally between magnitude 4.57 and 4.69 —a swing so faint only patient monitoring catches it. An RS CVn variable whose rhythm is set by the spots rotating across its surface.