Algol (beta Persei) is an eclipsing binary star system in Perseus. This means that two stars in orbit around each other will peroidically eclipse each other (one passes in front of the other). When an eclipse occurs, the brightness of the stars that we see from earth decreases. We can't see the two separate stars from earth, even in a large telescope, but even by naked eye, we can see the change in brightness.

By making simple brightness estimates of Algol, amateur astronomers can contribute to the knowledge of how this system works, and characteristics of the stars. It's not necessary to use a telescope. Algol is visible by eye to anyone who knows exactly where to look. These brightness estimates are used by professional astronomers to refine their model of what Algol is believed to consist of.

In this exercise, we will:

  • learn about eclipsing variable stars
  • learn how to make naked eye magnitude (brightness) measurements of a star
  • collect the measurements across many cycles of Algol's orbit
  • discover the orbital period of Algol and it's companion star
  • plot a light curve of the magnitude data
  • determine anything else we can discover about Algol from the light curve
Although the Algol system has been extensively investigated by astronomers already, there is always the chance that something new will be discovered. Any change in the orbital period, for instance, may indicate mass transfer from one star to the other. A change in the shape of the light curve, could indicate a shifting orientation of the orbit with respect to earth.