Telling Time by the Sky: Practice Problem Solutions

1. The gnomon is the pointer that casts the shadow. It is tilted to point at the north celestial pole, so its angle with the ground equals the latitude.

2. At solar noon. It points due north.

3. Mark the end of the shadow every 15 minutes. The shortest shadow marks solar noon, and the line from the stick to that mark points north-south.

4. Any two of: time zones (the Sun peaks earlier at the east edge of a zone), daylight saving time, and the equation of time (Earth's elliptical orbit and tilt shift solar noon by up to about 16 minutes).

5. The figure-8 path traced by the Sun's position at the same clock time through a year, because of the equation of time and the tilt.

6. 1900 is not a leap year (a century year not divisible by 400). 2000 is a leap year (divisible by 400).

7. The shadow swings from west to east during the day, since the Sun moves east to west.