Sky & Telescope Articles: If you can find the Pleiades, you can find Algol. During early evenings in February, the Pleiades will be high in the sky overhead, and towards the west as evening progresses. Algol is just north of the Pleiades, in the constellation Perseus. So stand looking west, look high overhead to see the Pleiades, then look towards the right (north), to see Perseus. Use the finder charts: to see what the star field looks like. Once you identify Algol, compare it to the other stars shown in the charts. The numbers on the chart indicate magnitude, with the decimal point omitted.

Normally, Algol is a magnitude 2.1 star, plenty bright enough to be seen even in urban skies. But about every 3 days, one of the stars eclipses the other, causing it's magnitude to drop to about 3.4.

Like any scientific experiment, one cannot let preconceived notions spoil the observations. Although we know that Algol varies from 2.1 to 3.4, there may be surprises! In 2000, naked eye observers noticed a star in Scorpius, Delta Scorpii, that had suddenly increased in brightness, where no variability was known to exist before.

Another issue of observations is the random nature of the errors. As long as there are no systematic offsets to the observations, random errors will tend to cancel each other out.