There is another type of variables quite distinct from the Mira stars.
These run through smaller light-changes in much shorter periods, also
they change abruptly with clockwork regularity, and the spectrum shows
no bright lines at maximum, indicative of physical change.
The first known was Algol, the Ghoul or Demon Star in Perseus,
and the brightest southern star of the Algol type is δ Librae. It
shines steadily for a little more than two days as a fifth-magnitude
star, then in a few hours drops suddenly to below sixth magnitude,
becoming invisible to the naked eye, and as quickly recovers its usual
brightness. The entire change takes place regularly in less than two
and a half days.
A few bright Algol stars in the south are: