Ancient Skywatchers: Practice Problem Solutions

1. Stonehenge marks the summer solstice sunrise (and winter solstice sunset). The Newark Earthworks octagon lines up with the Moon's extreme rising points. Cahokia's Woodhenge marked solstices and equinoxes.

2. A pattern in which eclipses repeat about every 18 years and 11 days, found by Babylonian astronomers.

3. About 7.2 degrees, which is 1/50 of a full circle (360 / 7.2 = 50).

4. The shadow angle is 1/50 of a circle, so the distance between the two cities is 1/50 of the Earth's circumference: 800 km x 50 = 40,000 km.

5. The magnitude scale, ranking stars from 1 (brightest) to 6 (faintest).

6. A slow shift in where the sky's pole points, caused by a wobble of Earth's axis. One cycle takes about 26,000 years.

7. Its first appearance in the dawn sky came about when the Nile began its yearly flood, so it worked as a calendar signal.