VARIABLE STARS

stars whose light fluctuates periodically. Many you sands of these stars exist, but the reason for the variation in their brilliance is not yet definitely established. One theory is that they are dying suns, their variability being due to periodical bursting of the molten interior through the shell of heavy vapors surrounding them. Another theory put forward by Profe or Lockyer suggests that the sudden illumination is caused by the pa age of the star through a swarm of meteors. Yet another suggestion is that the lo of brilliance is due to ‘sun spots’ of immense size. In one cla of these stars the cause of the variation has been discovered, but the explanation in these particular cases cannot be generally applied. In the cla referred to, of which the star Algol is the chief example, fluctuation has been found to be due to occultation of the light of one star by another of le brilliance. In the ease of Algol, the light from the star is reduced for several hours every third night. In recent years, it has been Gis covered that two stars exist, revolving around 2a common center. One of these was formerly believed to be a ‘dead’ star, but more recently it has been shown to be alive but much dimmer than its ‘twin.’ When the dim star pa es between the earth and the bright star, partial occultation occurs, manifesting itself as an apparent diminution in the light of the star.