How the Sun and Moon Can Appear to be the Same Size
The diameter of the Sun is over 400 times the diameter of the Moon. So how
can they appear to be the same size? Try this experiment! You need three
people for this activity.
1.Have one person hold out the large ball, which will represent the Sun. Hold
it out away from your body so that your hands are on the top and bottom of
2.Have another person hold up the small ball (representing the Moon) directly
in front of the "Sun". Stand about 6 feet away and hold the ball out in the
same way the person is holding the "Sun".
3. The third person should stand in front of the person holding the "Moon", looking toward the person holding the "Sun". This person will represent what
someone on Earth would see. Have the Sun and Moon adjust themselves so that
they appear to be in a straight line, with the Moon between the Earth and
4.The person holding the Sun should begin moving away from the person holding
the Moon (again keeping the Earth, Moon, and Sun in a straight line) until
the Sun and the Moon appear to be the same size to the person representing
Measure and record the diameters of the Sun and Moon.
Measure and record the distances from the Earth to the Moon and the Sun when
they appear to be the same size.
- 1 dodge ball or beach ball
- 1 softball or tennis ball
- tape measure or meter stick
- Why do you think they look the same size to the Earth observer?
- What happens when you look at the values of distance/diameter for the Moon
- Given what you know about the relative sizes of the Sun and Moon, what
can you conclude about their relative distances from Earth?
The StarChild site is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC.
The StarChild Team
StarChild Graphics & Music:
StarChild Project Leader:
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