Revolution of the Algol System

This animation illustrates the realistic 3-dimensional motion of the Algol eclipsing binary system. The perspective is from the Earth, as we would see the system if we could resolve the individual stars. The blue object is the B8 star and the red object the K2 star of the Algol system. The axes represent angle on the celestial sphere and are labeled in thousandths of an arc second (milli-arcsec) with respect to the center of mass. North is towards the lower right.

Notice the substantial distortion of the K2 star by the gravitational influence of its companion. Can you locate the center of mass by watching the motion? Can you tell which star is more massive? To answer these questions, you may find it useful to use the controls to stop the animation and step it forward or backward a step at a time.

The button labeled "Crosshairs On" toggles a set of crosshairs with digital readout that can be used to locate a point precisely. Once toggled on, clicking with the mouse causes the crosshairs to jump to the cursor and to follow the cursor as long as the mouse button is held down. Horizontal (x) and vertical (y) coordinates in milli-arcseconds are read out continuously as the cursor is moved. Toggling "Crosshairs Off" hides the crosshairs.

The distance to Algol is about 28.5 pc or 92.8 ly. This can be used to convert the angular measure of the animation (given in milli-arcsec) to actual physical distances. To do this, you will find the small-angle formula calculator to be of use. Usage: Click "Play" to begin and "Stop" to pause the animation. "Step" moves forward one step and "Back" moves backwards one step. "Home" returns to the beginning from any point. The position crosshairs can be toggled on and off as described above using the "Crosshairs On/Off" buttons.