Optional Assignment #2 Answers


There is 24 hours of night at the N. Pole in both figures.  That's what tells you this is the N. Hemisphere winter solstice.  The next figure explains why the earth might appear tilted to the left or the right on the winter solstice.

In one case you are standing at Position A and looking at the earth as it orbits the sun.  If you were to move to Position B and look back at the earth it would appear to be tilted to the right.

As the figure below shows, the fall equinox occurs on Sept. 21 in the N. Hemisphere and on Mar. 21 in the S. Hemisphere.

Names for the N. Hemisphere are given in green, the names for the S. Hemisphere are given in red. 



The best way to try to answer a question like this is to start with what you know.  The sun is overhead at noon on the equinoxes at the equator.  It is overhead at 23.5 N latitude on June 21 and at 23.5 S latitude on Dec. 21.  Plot these points on a graph and connect them with a line.


The sun appears overhead at noon sometime during the year only in the narrow band between 23.5 S and 23.5 N latitudes.

The sun path diagrams for Tucson and Minneapolis for the summer and winter solstices are shown below (these were the photocopied class notes).




As the following figure shows, the sun will be above the southern horizon at solar noon.  Shadows cast by objects on the ground will point north.





Refer back to the Answer for Question #5.  In the winter the days are shorter and the sun is lower in the sky in Minneapolis than in Tucson.  Both factors work to reduce the amount of sunlight energy reaching the ground in Minneapolis, so Minneapolis is colder than Tucson.  In the summer the days are longer (works to increase amount of energy) but the sun is lower in the sky (reduces amount of energy).  The 2nd factor is dominant and less energy reaches the ground in Minneapolis than in Tucson.




On Mar. 21 (spring equinox) the days will be 12 hours long.  Jun 21 is the longest day of the year, so the days are longer than 12 hours and getting longer between Mar. 21 and Jun. 21.  Between Jun 21 and Sep. 21 the days are more than 12 hours but getting shorter.  The days are again 12 hours long on Sep. 21, the fall equinox.  Between Sep. 21 and Mar. 21 the days are less than 12 hours long.



In Question #19, the days are 12 hours long at the equator (that is always true) and 24 hours long north of the Arctic circle.  So the days get longer as you move from the equator toward the N. Pole.


A typographical error caused some confusion on this problem.