classical cepheids (also known as population i cepheids, type i cepheids, or delta cephei variables) pulsate with very regular periods of the order of days to months. classical cepheids are population i young variable stars which are 4–20 times more massive than the sun, and up to 100,000 times more luminous. cepheids are yellow supergiants of spectral class f6 – k2. when they pulsate, their radii change by ~25%. for the longer-period i carinae this means millions of kilometers for a pulsation cycle.