Algol or ( β Persei ) is one of the most exciting variable star that can be easily observed even from moderately light polluted sky. It is an eclipsing binary star. The period is period is 2.867328 days or 2days 20hrs 48min 57sec. The eclipse takes place roughly over 10 hours. The star remains at its near-constant magnitude of 2.1 and fades to 3.4 magnitude (called minima) in about 5 hours and then returns back to its constant magnitude in next 5 hours.
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Algol can be compared with Gamma (γ) Andromedae (mag 2.1) which is to its west and Epsilon (ε) Persei (mag 2.9) ~0.5 mag brighter than when Algol is at minima.
For Sky and Telescope article and map <click here>.
The best time watch the entire sequence of Algol going to minima and coming back to its normal magnitude is when the minima takes place when the star transits local meridian, which happens around 8th of November.
At other times one can observe the partial sequence of fading or becoming bright.
As the star is very bright even full-moon is no hindrance when observing from a fairly dark site.
You may use this map to identify the star.
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