Volunteers walking the orrery

The Human-Powered Orrery is a kinesthetic model of planetary motion in the inner solar system. Most solar system models made in classrooms are simple line-ups of the planets in a straight line with no indication of how the planets move. The Human Powered Orrery is a 3-dimensional model where the planets are laid out first in two dimensions spatially along orbit lines, then set in motion to show how the planets closer to the Sun orbit faster than the outer planets. So the 3rd dimension in this model is time. Students take turns acting out the planet movements taking 2-week long steps.

The original write-up (18 pp) is the last one listed below, from the GEMS Space Science Sequence. A simpler 2-page write-up appeared on the back a poster published in NSTA journals in 2008.

• 2015 Revision (PDF, 1.58 MB); 2015 Revision (Word, 1.08 MB)
• Poster version (2 pp; PDF, 760Kb)
• Original GEMS Space Science Sequence version (PDF, 580 KB) (18 pp)

Improved materials for Human Powered Orrery, using circumference ropes with tapes at 2 week intervals. The ropes can be easily wound up and unwound from cardboard spools for re-use for many classes.

The 2015 version has a major improvement in materials preparation over previous versions. In early versions, students measure out the radius of each planet's orbit using a 2.5 meter piece of thin rope or string with knots tied along the rope to measure the scale distance to each planet: 58cm (Mercury), 108cm (Venus), 150cm (Earth) and 228cm (Mars). The rope was used to trace out radius distance to orbit lines along which students use masking or painter’s tape indoors or chalk (outdoors) to put marks at 2-week intervals.

A far less time consuming technique is to make rope circles as the actual circumference lines of the orbits, with tape markers placed at two week intervals along each rope circle. The advantages of this are that it takes less class time to set up, and it's completely re-usable; the same ropes can be stored and re-used many times. Putting pieces of tape or chalk marks directly on the floor or ground are temporary; not re-usable.

The table below gives the scale model measurements for lengths of rope needed as well as the 2-week intervals to mark along the rope.