The sky's changing phenomena have always been a source of wonder. Nearly all the changes seen with the unaided eye result from the movements of solar-system objects. But far in the background, a number of bright variable stars can also be followed through their brightness cycles without optical aid. Compared to most of their telescopic counterparts, the naked-eye variables are easy to find. Once you know a few of them, you can check on how they are doing whenever you look up at the sky.

Thirty-four variable stars have a range of at least 0.4 magnitude and become brighter than visual magnitude 4.0, according to the authoritative General Catalogue of Variable Stars (GCVS) and its supplements the Name-Lists of Variable Stars. (This doesn't include novae or supernovae, which occasionally reach naked-eye brightness.) Among these stars are many eclipsing binaries, Cepheid variables, and semiregular red variables, as well as a few long-period stars of the Mira type and the recurrent nova T Coronae Borealis. As many as 24 do not fade below magnitude 5.1 and so remain visible to the unaided eye all the time. It's interesting that only seven of these are south of the celestial equator, compared to 17 north of it. Could there be several undiscovered naked-eye variables in the southern sky waiting to be noticed?

Here is a personal list of my dozen favorite northern naked-eye variables, in no particular order. (I'd include Epsilon Aurigae, except that its next two-year eclipse doesn't begin until 2009!) Many types of variable stars go unrepresented in this sample, since many are low-luminosity objects too faint to be visible without a telescope or vary too slightly for their changes to be visually noticeable. Small binoculars will help in observing the fainter phases of some of these stars, especially if you don't have really dark skies.

All the light curves in this article resulted from hundreds of naked-eye observations by the author in 1987-88. Each plotted point is the average of between seven and 11 brightness estimates made on different dates. For clarity, data are repeated to cover more than one cycle.