December has always been a season of lights. For centuries humans have been lighting trees, lighting candles and more recently lighting homes. Much of this obsession with lights comes from the fact that December is the time of the winter solstice, a time when the sun is lowest in the sky and the nights are longest.

From the days of flickering candles we have moved into the modern era of flashing LEDs. Ancient astronomers knew that sometimes the stars blinked on and off as well. During December, the most famous of these stars is well positioned for observing, and you don't even need a telescope to see it.

The star Algol, or b Persei, is the second-brightest star in the constellation to Perseus the Hero. In December, Perseus is almost directly overhead. It is easily found by locating the W shape of Cassiopeia and moving down toward the eastern horizon. The J, or fishhook, shape is Perseus. Looking about half way between Cassiopeia and the Pleiades star cluster, we find Algol, which in ancient times was referred to as the "Demon Star." This designation comes from the unusual behavior of the star. Over three days, the star dims from magnitude 2.1 to 3.4 and then slowly brightens again.

The continuous dimming and brightening of Algol is easily visible to the naked eye, but it wasn't until modern astronomy that a reasonable explanation for the flickering was offered. Today we understand Algol to be what is known as an eclipsing binary.

Stars of this type are binary star systems in which two stars orbit around a common center of gravity. In the case of the Algol system, the primary star is a white star about 100 times more luminous than the sun. The secondary star is a yellow or yellow-white star similar to our sun. The orbit of the secondary star is such that it passes directly in front of the primary star. This eclipsing causes the light of the primary star to drop. Oddly enough, the light of the primary star is so bright, the secondary star is totally lost in the glare.

The existence of the secondary star was only proven in the late 1970s, when the spectra of both stars were analyzed.

Observing the changes of Algol's magnitude require being outside on successive nights. It also requires careful observation, even if no optical aid is used. This can be a challenge on December nights in Wyoming.

The planets Venus and Jupiter are in close conjunction with the waxing crescent moon this time of year. As December rolls along Venus will slowly creep higher into the sky while Jupiter will continue closer to the glare of the sun. But don't pack up the telescope just yet. By Christmas Eve, Mercury will be moving into the evening sky. At the end of the month another conjunction will occur, this time between Mercury, Jupiter and the crescent moon.

While the lights we see from planets are merely reflected lights, they are far brighter than any of the stars in the sky. However, unlike eclipsing binaries such as Algol, the planets shine with a steady unwavering light. Yet no matter which light draws you outdoors this holiday season, don't forget to look up and observe the lights that have inspired humans for thousands of years: lights that brighten this cold, dark season.

Rod Kennedy is a technician at the Casper Planetarium. He can be reached at 577-0310 or rodk@tribcsp.com.