Observing the motion of the Sun
Practical Activity for 14-16
Tracking the motion of the Sun through the sky for a day, month or year.
Apparatus and Materials
- Either: Card with hole in it
- Or: Bowl (transparent, plastic, hemispherical), Card (large piece), Card (smaller, with hole in it)
Health & Safety and Technical Notes
It is essential to remind students that they must never look at the Sun directly, not even through a pinhole camera. This could blind them.
One way to observe the Sun's changing position is to put a card with a hole in it on a window which faces the Sun. A bright spot will appear on an opposite wall. A short time later, move the card so that the same spot on the wall is illuminated, and mark the position of the hole in the card on the window (with a yellow sticker?). Record the path of the Sun until it disappears from that window (but there may be other convenient windows). This demonstration can be continued at daily/weekly intervals.
A second way to observe the Sun's changing position over the course of a day is to invert a transparent plastic hemispherical bowl on a large piece of card on which the central point is marked. Place a smaller card with a hole in it on the surface of the bowl so that the Sun shines down onto the central spot and the position of the hole in the card can be marked on the hemisphere. Repeat this throughout the day and for as many days throughout the year as possible.
- Ask students to watch the Sun and its daily movements, if possible from month to month, so that the changes in the height of the Sun's daily arc can be observed.
- Over a period of time, note the star pattern in the vicinity of the Sun immediately after sunset and before sunrise.
Students should note the Sun's position at noon from month to month (take care if summer time is introduced).They should note the height of the Sun at noon at different times of the year. The Sun's path changes with the seasons: high in the sky in mid-summer and low in mid-winter. It rises precisely in the east to set in the west on those days which we call the spring and autumn equinox, (at about 21 March, 22 September), when day and night are equal in length.
This experiment was safety-tested in April 2007
Geoff Sargent: Mon 2 February 2009
Use software eg Winstars2 or Photodesk's Orrery. Either will model the sky from any point on the surface of the Earth and produce animations which show precisely what happens as declination changes.
Photodesk's Orrery permits the position of the observer to be dragged in real time about the Earth in real time as the animation runs. Interesting discussions.