Download The Seasons

The Seasons
Autumn
Winter
Summer
Sun
Spring
Winter
Celestial
Equator
Spring
Celestial
Equator
Summer
Celestial
Equator
Autumn
Celestial
Equator
Winter Observations
What is the orientation of the earth’s axis in relation to the sun when the northern hemisphere
experiences winter? (Pointed away)
What is the sun’s position in relation to the celestial equator during the winter? (23 degrees
below) Where on the globe (in latitude) would the sun appear directly overhead on the winter
solstice? (Tropic of Capricorn, or 23 degrees south of the equator)
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Summer Observations
What is the orientation of the earth’s axis in relation to the sun when the northern hemisphere
experiences summer? (Pointed towards)
What is the sun’s position in relation to the celestial equator during the summer? (23 degrees
above) Where on the globe (in latitude) would the sun appear directly overhead on the summer
solstice? (Tropic of Cancer, or 23 degrees north of the equator)
Comparison of Winter & Summer
Compare the area of illumination for the winter and summer solstices. Which season experiences
a greater intensity (greater concentration) of light? Summer
Run the simulation again without stopping and note the distance and the speed of the earth as it
orbits the sun. While the simulation is not to scale and greatly exaggerates the motion of the
earth, it accurately depicts the changes in distance and speed of the earth as it orbits the sun.
Comparison of speeds between summer and winter:
The earth orbits the earth faster in the winter than the summer.
Comparison of distances between summer and winter:
The earth is closer to the sun in the winter than in the summer.
The dates of the equinoxes and solstices are given in the table below. Determine the number of
days for each season during 2011.
2011
2012
Spring begins, March 20, 2011
Spring begins, March 20, 2012
Summer begins, June 21, 2011
Summer begins, June 21, 2012
Autumn begins, September 22, 2011
Autumn begins, September 23, 2012
Winter begins, December 21, 2011
Winter begins, December 21, 2012
March 20, 2011 – June 21, 2011
Number of days: 93
June 21, 2011 – September 22, 2011
Number of days: 93
September 22, 2011 – December 21, 2011
Number of days: 90
December 21, 2005 – March 20, 2012
Number of days: 89
What is the relationship between the speed of the earth in its orbit with the length of the season?
Winter is the shortest season. The faster the orbital speed the shorter the season.
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It is the gravitational attraction between the sun and the earth that keeps the earth in its orbit.
Remember Newton’s Second Law of Motion, it states that in order to accelerate a mass a force
must be applied to it. What can you say about the relationship between the magnitude of this
force and the distance the earth is from the sun?
The closer to the earth to the sun, the greater the gravitational force between the earth and the sun.
Newton’s Second Law states that the greater the force the greater the acceleration.
Construct a statement (or series of statements) that illustrates the relationship between the
duration of winter and summer, the distance from the sun, and speed of the earth as it orbits the
sun.
The earth is slightly closer to the sun and has a greater orbital speed in the winter. Since the earth is
moving faster during the winter, it takes a shorter time to travel ¼ the way around the sun.
Most people would expect that the earth is closer to the sun during the summer and farther from
the sun in the winter. As you have seen this is not true. What factor is responsible for the degree
of heating the earth’s surface as the earth orbits the sun?
The tilt of the earth’s axis. This factor changes the concentration of the sun’s rays that reach the
earth’s surface. At low latitudes (the tropics) the light is more directly overhead (perpendicular to the
earth’s surface) and more concentrated. At higher latitudes the sunlight hits the earth’s surface
more obliquely. This increases the area of illumination thus the amount of light per area is less at
higher latitudes.
Comparison of Solstice and Equinox Observations
Activate the simulation and stop the orbiting of the earth at two locations, the Autumnal equinox
(fall) and the Vernal (spring) equinox.
What is the sun’s position in relation to the celestial equator during the equinoxes? Where on the
globe would the sun appear directly overhead on the summer solstice? (Use a globe for reference.)
The sun is directly on the celestial equator, thus the sun is directly overhead on the equator.
Compare the area of illumination at the equinox to the summer and winter solstices.
The area of illumination at the equinox is less than at the winter solstice and more than at the
summer solstice.
Notice that the earth’s axis always points to the same direction in space. The northern pole always
points to a location in the sky where we find the North Star, or Polaris. In a later laboratory we will
observe the motion of the stars around Polaris to show that the location of Polaris in the sky does not
change either during the course of the evening or during the progression of the seasons.
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Use the globe and small yellow sphere as the sun and physically manipulate the orientation of the
earth as it orbits the sun. Make a complete seasonal cycle.
Use the small flashlight to simulate the illumination of the sun. Place it perpendicular to the
globe’s surface and notice the area of illumination on the globe. Now change the position of the
flashlight so it is more oblique to the globe’s surface. What happens to the area of illumination?
When the flashlight is perpendicular to the earth’s surface the area of illumination is smaller and the
intensity of illumination is greater. As the flashlight is tilted to the earth’s surface, the area of
illumination is greater and correspondingly the intensity of the light is less.
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