[ο Ceti was found to fade, disappear, and appear again during 1595-1596 by David Fabricius. Later, an 11-month period was established. Other similar long-period variables (P > 100 days) are called collectively as Mira variables.]
[Mira variables show significant evidence of mass loss, e.g., split of the OH-maser radio emission line or the presence of P Cygni lines, which are lines of absorption nature at the blue side and emission at the red side.]
[In 1784 John Goodricke found δ Cephei varies with a period of 5 days 8 hours 48 minutes. This class of stars are called the Cepheids, with periods > days.]
Evidence for size pulsations
[RR Lyrae variables have lower masses and periods < 1 day. They are metal poor, population II stars.]
[This is a very important method of estimating distance in astronomy. Check how far one can go with this method. In the figure, W Vir stars are also called Type II Cepheids, which are Population II stars, while the Classical (Type I) Cepheids are Population I stars.]
