global day/night


 
A globe can be used to visualize how the earth is illuminated by the sun. This will show why the sun shines throughout the night in the artic circle during the start of the northern hemisphere's summer and why at the same time no sunlight falls in the middle of the day within the antartic circle. You will also be able to see why the sun hovers at the horizon on March 21 at the north pole causing a sunrise lasting 24 hours and why there are more daylight hours in the summer.
 
To demonstrate these things, in a darkened room, illuminate a globe with a single lamp placed a few feet away from the globe with the light at the same height as the globe. The side toward the lamp will be lighted just as the earth is lighted by the sun. Turning the globe slowly about its axis causes the light to move across its surface just as daylight moves across the earth as the earth rotates.
 
Turn the base of the globe's mounting until the north pole is tilted toward the light. This corresponds to June 21 and the first day of summer in the northern hemisphere. Turning the base 180 degrees so the north pole is away from the lamp corresponds to December 21 and the first day of winter when days are shortest of daylight hours in the northern hemisphere. On this day summer begins with the day of longest daylight in the southern hemisphere. Turning the base halfway between these two positions corresponds to the equinoxes on March 21 and September 21. At those times the dividing line between night and day will pass through both poles and everyone on earth experiences days with 12 hours of daylight and 12 hours of night.
 
An interesting variation of this demonstration is to remove the globe from its mounting and carry it outside. Place the globe where sunlight will fall on it and orient it exactly as the earth is oriented. To do this find your location on the globe. Turn the globe so that this spot sits at the very top of the globe. Keeping this spot at the top, turn the globe so that the north pole is facing north. The globe is now turned just as the earth is turned and is illuminated by the sun just as the earth is illuminated. All spots on the earth lit by sunlight also have their corresponding representations on the globe lit by sunlight. If the globe is left in position 24 hours, the area lit by sunlight will advance across its surface just as daylight advances across the earth. If left for a year the axis of the globe will move in unison with the axis of the earth, both spheres undergoing simultaneously the same effects, allowing you at a whim to view the present stage of the entire process.