Solar Eclipses Demonstration
Practical Activity for 11-14
A ball fixed to a hula hoop is used to model how the Moon’s inclined orbit to the Earth means we do not get a solar eclipse every month.
Apparatus and Materials
- A plastic ball
- A hula hoop
- 3 lamps with card cylinders attached
Health & Safety and Technical Notes
- You will need to attach your ball to the hula hoop. You could do this in many ways, such as velcro, glue, sticky tape etc... or you could cut the ball in half and fix it either side of the hoop more permanently.
- The Moonʼs orbit is inclined to the ecliptic plane (the plane of the solar system that includes the Earthʼs orbit and the Sun) by about 5 degrees. This means that only at certain times does the Earth, Moon and Sun achieve a line of sight effect that can cause the Moon to pass between the Earth and Sun.
- The Sun is much further away from the Earth than the Moon, so although it is much larger than the Moon, it only appears as big as the Moon in the sky. This allows the Moon to completely cover the Sun during a total eclipse.
- Not all eclipses are total, sometimes the Moon does not pass directly in front of the Sun because the alignment of the various orbits is not quite exact enough. This causes a partial eclipse. On other occasions slight variations in the various orbits mean the Moon is too far away from the Earth to appear big enough to cover the Sun. This is called an annular eclipse.
- The eclipse effect in this demonstration is quite easy to see, and members of a class could take it in turns to see this effect, or you could photograph it (or use a webcam) and show it on a screen.