Seasons #6 is a challenging activity. Each planet has a different tilt and period of rotation. Only half of a planet is shown in each diagram, so each diagram represents half a rotation (half of a planetary day).
Letâ€™s look at Station #5. This planet has a tilt of 21Ëš and a period of rotation of 40 hours. So we know right away that if a full spin is 40 hours, then a half spin is 20 hours. Students have to estimate how many hours each point (A,B,C,D or E) will spend in daylight and in darkness during this half spin. For a non-tilted planet, daylight and darkness is evenly divided. However, that changes when a planet is tilted. Also, notice that even on a tilted planet, any point at the equator experiences equal hours of daylight & darkness. However, points N or S of the equator have different hours of daylight and darkness. In diagram #5, follow the path of point A (60Ëš N latitude) as it rotates with the planet. Most of its path (3/4) is spent in darkness and less (1/4) in light (day). My estimate is that point A spends about 14 hrs in darkness and 6 hrs in daylight during this half spin. We need to double these numbers, since pt A has to rotate across the backside (unseen) of this planet also. So, pt A has 28 hrs of daylight and 12 hours of darkness each day. Now, point B will be different. Follow pt B (30Ëš N latitude) as it rotates with the planet. Notice it spends a little more than half of its time in darkness. My estimate is 12 hrs of darkness and 8 hrs of daylight during a half spin. So double these numbers for a full spin (day), and pt B would spend 24 hrs in darkness and 16 hrs in daylight each day. Numbers in the southern hemisphere will be exactly opposite those in the northern hemisphere.
* Notice that 3 longitude lines/meridians run N-S to divide each diagram into four equal parts. Use these meridians to help estimate hours of daylight and darkness.
* We always allow student answers to be within a reasonable range (within 1 or 2 hr).
* This is activity #6 for a reason! It is challenging! We find that we always have some students who â€œjust donâ€™t get itâ€.
Thank you very much. You asked a very good question. And I hope this helps.
April 18, 2010