Go outside the next clear evening at around 7 to 8 p.m. and look up high in the southeast (assuming you live in mid-northern latitudes). The star Algol will be winking at you! The wink is pretty slow - in fact it takes a bit short of three days. The changing brightness of this easily visible star, however, is obvious if you take notice and compare it with stars of similar magnitude nearby. Although also known as Beta Persei, I stick with its old Arabic name, Algol. The star is one of the most prominent in the constellation Perseus, the Champion. You can look for this star pattern as soon as it gets dark. In mid-December at 6 p.m., Perseus, including Algol, appears high in the east. By 9:30 p.m., Perseus is due south, and almost at the zenith (the point straight up) as seen from near +42 degrees latitude, close to where I live in northeastern Pennsylvania. By 4 a.m., Perseus is still visible, low in the west-northwest. Algol is a short-period variable star. It is usually magnitude +2.3, but regularly, at intervals of two days, 20 hours and 48 minutes, the star’s brightness wanes to minimum light of +3.5. It stays near minimum for about two hours, and then waxes to maximum magnitude of +2.3. It has kept up this behavior since anyone can remember, without fail! The varying magnitude was first noted in 1672 by the Italian astronomer Geminiano Montanari. Eventually, the cause of the fluctuations became clear. There is an unseen, dimmer companion star circling Algol, partially eclipsing the brighter star. This was confirmed in 1889 by Potsdam astronomer Hermann Carl Vogel, using a spectroscope. (Note: On the magnitude scale, the bigger the number, the fainter the star appears. The faintest stars we can typically see without optical aid on a dark, moonless night, away from distracting man-made lights and with dark-adapted eyes, are approximately magnitude +6. The bright yellow star Capella, visible high in the east on a mid-December, early evening, is magnitude 0.08. The Big Dipper’s brighter stars are +2.) Algol is currently around 92.8 light years away from the sun; it takes that many years for the starlight to reach us. The two stars are only about 0.062 astronomical units apart. That’s about 5.7 million miles. Mercury, on average, is 36 million miles from the sun; the Earth is about 93 million, which is the same as one astronomical unit. There is also a third star in the Algol system. To find the constellation Perseus in early evening, face east-northeast and look high up for the easily seen, M-shaped five-star pattern of Cassiopeia. To the lower right are the stars of Perseus. Perseus can be traced like a stick-figure of a man. In this case, the principal stars closer to Cassiopeia seem to form his head and pointed cap. Algol is near Perseus’ “left foot” (if you imagine seeing Perseus “face-to-face”). His “right foot” can be traced by other stars, which so happen to lie very near the compact, bright star cluster, the Pleiades. Numerous “open” star clusters abound in Perseus, some visible with binoculars. Around Aug. 11-12, one of the strongest, regular meteor showers of the year, the Perseids, seem to radiate from this constellation. You can find information in monthly astronomical publications giving the times when Algol reaches minimum light. There are also sources online. Some have a star chart to compare Algol’s light with nearby stars with the magnitudes labeled. Often times, minimum brightness happens when we can’t see it because it is daytime here or Algol is below the horizon. Listed here are the times we will be able to see Algol’s minimum from the Eastern time zone, through the end of January 2020 (Eastern Standard Time): 3:12 a.m. Dec. 22; 12:02 a.m. Dec. 25; 8:51 p.m. Dec. 27; 5:40 p.m. Dec. 30; 4:57 a.m. Jan. 11; 1:46 a.m. Jan. 14; 11:36 p.m. Jan. 16; 7:25 p.m. Jan. 19. The moon, by the way, reaches last quarter on Dec. 18. Keep looking up! Peter Becker is managing editor at The News Eagle in Hawley, Pennsylvania. Notes are welcome at firstname.lastname@example.org. Please mention in what newspaper or website you read this column.