1. Around the world, farmers know that for most crops, you plant in the spring and harvest in the fall. But in some regions, there is not much differentiation between the seasons. Since different constellations are visible at different times of the year, you can use them to tell what month it is.

2. Scorpius is only visible in the northern hemisphere's evening sky in the summer. Some historians suspect that many of the myths associated with the constellations were invented to help the farmers remember them. When they saw certain constellations, they would know it was time to begin the planting or the reaping

3. Circumpolar Constellations Constellations that never “set” In the Northern Hemisphere, some constellations set east to west, but some always stay visible in the night sky.

4. Retrograde motion The apparent backward motion of planets against the background stars.

5. Mars retrogrades for 72 days every 25.6 months. Jupiter for 121 days every 13.1 months. Saturn for 138 days every 12.4 months. Uranus for 151 days every 12.15 months and Neptune for 158 days every 12.07 months.

6. http://www.youtube.com/watch?v=72Fr Zz_zJFU&NR=1&feature=fvwp