Solar Observations

The shadow points on these two shadwo trackers were collected at Lawrence Hall of Science in Berkeley, California, on the same day at the same times. One varibable was different in the orientation of the sun trackers. What was that variable? Why are the points different?

The sunstones is a sculpture located at Lawrence Hall of Science. It is oriented so that from this view you are looking directly west. During what time of the year was this photo taken?

These shadows were traced during a teacher workshop in Sunnyvale, California, in August 1999. Which direction was the person facing whose shadow was being traced? Do you have enough evidence to be certain of your answer? What else would you like to know?

For more images of shadows and solar energy applications, check out FOSSweb at http://www.fossweb.com. If you’d like to get answers to these questions, you can e-mail Sue Jagoda at skjagoda @uclink4.berkeley.edu or look for the answers in the next FOSS Newsletter.

Answers to Solar Observations
p. 7 FOSS Newsletter, Spring 2001 Number 17

• The two Shadow Trackers were created on March 30, 1999. The top Shadow Tracker was aligned to true north, i.e. toward the north pole of rotation. The lower Shadow Tracker was aligned with magnetic north, i.e., the north towards which the needle points in a compass. These two "norths" can vary as much as several degrees. Magnetic north does not remain constant. You might have noticed a symbol on topographic maps referring to magnetic declination. This symbol tells how much difference there is between true and magnetic north. This information is useful when you are trying to find your way with a map and compass, i.e., orienteering. For more information about magnetic declination, check out these websites:

Canada Geologic Survey, http://www.geolab.nrcan.gc.ca/geomag/magdec_e.shtml

U.S. Geological Survey
Finding Your Way with Map and Compass
http://erg.usgs.gov/isb/pubs/factsheets/fs03501.html

• The photo of the Sunstones at Lawrence Hall of Science was taken during one of the equinoxes, either spring or fall (we don't know for sure). An equinox is when night and day are of equal length in all parts of the Earth. The word equinox comes from a Latin word meaning "equal night." At this time the Sun appears to rise and set directly over the Equator. It sets due west. For more information, check out this NASA website: http://istp.gsfc.nasa.gov/stargaze/Sseason.htm.

• The shadow tracings at the bottom of page 7 probably don't provide enough information for an accurate answer. Was the person whose shadow was being traced facing toward their shadow or away? If they were facing their shadow, the sun was at their back. So the longer shadow was taken during early morning hours when the sun was lower in the sky. The shorter shadow was drawn later in the day when the sun was almost overhead. If the shadows were drawn in the morning and the person was facing their shadow, they were facing to the west. Would the shadow have looked the same if they had been facing away from it? That's something to try out. (Some clues from the photographer: The person was facing their shadow in the morning.)