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SunTracker

Solar Water Pumping
Automata – 507 Mechanical Movements

To track the Sun and record its passage was another project that seemed worthwhile.

It is tricky for children, or anyone for that matter, to perceive that it is our planet that is moving relative to the Sun, rather than the Sun moving relative to the Earth. Our language is riddled with this false understanding of Earth-centrism. And while it is true the Sun is also travelling through Space, and the Earth travels with it in a spiral pattern, rather than the flat circular orbiting we were taught, it is best not to complicate things at this point.

SunTracker with compass, watch, and protractor

To make the SunTracker, I cut out and folded a thin piece of cardboard, and inserted a paper fastener through it at the back, in the middle, as near to the bend as possible, through a larger piece of cardboard (to provide stability). This allows the tracker to swivel. Upon this bigger piece of cardboard can be laid sheets of paper to record observations. (If there is wind about, you might want a rock or two to keep the assembly from blowing away.)

Above the perpendicular stick on the tracker, make a small hole in the cardboard. This hole allows light to shine through it, creating a dot in the shadow of the Sun-tracker.

The tracker must be aligned South, but it doesn’t necessarily have to stay in the same spot throughout the day as recordings are being made.

The idea is to position the tracker so that the stick casts no shadow. At that moment it will be pointing directly towards the Sun, and the plane of the tracker will be horizontal to the Sun’s incoming radiation. The tiny hole will allow light to make a dot on the paper.

Position the SunTracker so
that the stick casts no shadow,
mark where the dot of light falls.
Record time and angle.

It is possible such an exercise could engage up to four students – one adjusting the pointer so that is shadowless, another marking the dot at that moment, another recording the time, and another witnessing the angle of solar declination and recording it. Conclusions can be drawn from their observations. The recordings will appear different week by week and throughout the year, more noticeably the further one is from the equator.

One of the surprising things I learned playing with this is that, in the summer, our local clock time is quite a bit different from real solar time.

Natural noon occurs when the Sun appears straight South. (And of course, one must know their angle of declination from the magnetic north pole, and allow for that…see Compass Dude.) Another indicator for direct South is that the shortest shadows will be at noon. In this case the light dot will be at 90 degrees through the center of the paper fastener to the south edge of the cardboard.

Solar Water Pumping
Automata – 507 Mechanical Movements