Spiral Galaxy

This simulation models a Milky Way style disk of stars with a flat rotation curve, so stars move at a nearly constant speed while the spiral pattern turns at its own slower rate. Sliders change the number of arms from 2 to 6, the pitch angle and the time rate in millions of years per second, and scale rings show distance in light-years. Readouts track elapsed time, the Sun's galactic years, speed and period. It helps teachers show that spiral arms are density waves, not fixed groups of stars.

• Change Arms from 2 to 6 and compare how the pattern looks.
• Adjust Tightness (pitch) to wind the spiral tighter or looser.
• Raise Time rate and watch the Sun galactic years readout count up.
• Toggle Show scale rings to judge the size of the disk in light-years.
• Zoom out and tilt the view to see the whole disk, then zoom in among the stars.

1. 1Describe the shape and size of a spiral galaxy such as the Milky Way.
2. 2Explain that spiral arms are density waves that stars move through.
3. 3Estimate how long the Sun takes to orbit the galactic center.
4. 4Relate the pitch angle and number of arms to the look of a galaxy.

Questions teachers ask