Minima of Algol

One of the exciting observations is to watch Algol ( β Persei ) to fade and brighten again.   Algol is an eclipsing binary with period of about 2 days 20 hours.  For 2 days and 15 hrs or so it is a 2.1 magnitude star. Then it starts fading, it’s brightness decreases over next 5 hours.  At the ‘dimmest’, called minima, it is 3.4 mag star and then in next 5 hours or so it brightens back to its usual 2.1 mag. i.e. maxima.

Find Algol using this map.

Normally one does not see this entire sequence of fading and brightening.  However, if  a) the time of  minima coincides with the local midnight and b) at this time the star is transiting the meridian then one can  enjoy the entire sequence.

The upper culmination of Algol at local midnight takes place close to Nov 8 every year. If the minima of Algol takes place close to this day then the entire eclipse sequence can be followed in one night.  Even at the minima the star is quite bright and phase of the moon is not very disturbing.

Minima of Algol –  suitable times for for observations for observations in India please visit

You may please visit the sky and telescope site for the times of minima of Algol


About skytonight

I am the present Director of Nehru Planetarium of Nehru Centre Mumbai, India I like to talk about astronomy and sky observations to general public.
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