Algol, also know as Persei (26), HR936, HD19356, SAO38592,
at R.A.= 3h08m, dec=41° is an eclipsing
Algol's magnitude is typically 2.1, but every two days, 20 hours and 49 minutes
it dips to 3.4 for about 10 hours.
In the below Wiki image, the red arrow marks the location of Algol in Perseus.