In this lesson, you show why we experience night and day, the seasons, and the seasonal changes of light.

Open SeasonsOV.max.

Select the circle named Earth's Orbit and choose Edit > Clone.
In the Clone Options dialog box, choose Copy. Name the circle Around Earth's Orbit.
In the Modify panel, change the radius of Around Earth's Orbit to 400:

Open the Camera sub-panel and click Target.
In the Top viewport, create a target camera by dragging:

In the Motion panel, change the Position controller of the target camera from Bezier to Path:

       

Pick Earth for the Look At Target.
Pick Around Earth's Orbit for the Current Path Object:

    

The camera moves to the path. The camera's new target aligns to the Earth, leaving the old target behind:

In the Motion panel, drag downward on the %Along Path spinner. Move the camera backward along the path until it line of sight is perpendicular to the X-axis and makes an exact tangent to the Earth's Orbit:

  

 

Delete the Camera01.Target object.
Hide the Moon, the Moon's Orbit and the Earth's Orbit.

Click Render Scene to open the Render dialog box.
In the Output Size group, click 320 x 240.
In the Render Output group, uncheck Save File.
Then click Close:

  

Press C to display the view from the Follow Camera.
Right-click on the Camera01 viewport label and choose Show Safe Frame.
The safe frames appear in the view, but the Earth looks far away:

In the Modify panel, set the camera lens to 200 mm:

The Earth enlarges in the view. Fine-tune its apparent size by adjusting the Lens spinner:

Hide the grid, the Moon, and the Moon's orbit.
Click Quick Render to test the results:

In this close-up view, the the Equator, the Earth's Poles, and the Earth's Orbit seem too thick.
Open the Modify panel and change the Thickness of each one in the General rollout from 1.0 to 0.5.
Click Quick Render to see the result:

  

 

Click Render Scene.
In the Render dialog box, choose Active Time Segment.
Click Files. Name the file SeasonsFC and choose the AVI file type.
Click OK and Close.

Choose File > Save As. Save the file as SeasonsFC.max.

Render the scene from the Follow Camera.

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Hide the Follow Camera and the Overview camera.
Delete Camera01.Target.

Press H and select Earth's Orbit.
In the Front View, shift-clone the orbit by holding down the Shift key and moving the Earth's Orbit upward in Y:

Name the copy Above Earth's Orbit:

Create a Target camera and assign it a Path position controller.
Pick Earth for the Look At Target.
Pick Above Earth's Orbit for the Current Path Object.
The camera moves to the path and looks directly down at the Earth:

  

Press C to activate the camera view.
Right-click the camera label and enable Safe Frame.
In the Modify panel, adjust the size of the Lens.
Name the camera Above the North Pole:

In the Front viewport, select the circle named Above Earth's Orbit.
In the Top viewport, move the circle to the left in X.
The camera flips 90° as you move its path.
Position the circle so that the camera is exactly aligned with the Earth's Pole:

  

Open Rendering dialog box and click the Files button.
Name the file SeasonsNP and choose the AVI file type. Then click Close.

Save your file as SeasonsNP.max.

Click Quick Render to render the scene.

To animate the seasons from the South Pole, shift-clone the Above the Earth orbit and the Above the North Pole camera and place them below the Earth. Or if you are in a hurry, open the Material Editor and rotate the coordinates of the Earth.jpg map 180° in W.

Name the output file SeasonsSP.avi.

Click Quick Render to render the scene.

Note: If you render to a compressed .mov file format, like as the movie that comes with this tutorial, you might want to hide the equator, since the red color does not turn out as well.

Save your file as SeasonsSP.max.

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Interpreting the Results

Choose File > View File to play the result of SeasonsFC.avi, SeasonsNP.avi and SeasonsSP.avi.

The Earth rotates on its axis as it goes around the Sun. Because the Earth is turning, different sides of the planet are lit over time. When it is day on one side, it is night on the other. Sunrise and sunset occur where the areas of light and the dark meet.

At the beginning of the animations, the majority of light falls on the Northern Hemisphere, where it is summer. Because it is the summer solstice, there is continuous light around the North Pole. Then the edge of illumination begins to shrink, moving across the North Pole at the fall equinox. At the winter solstice, the area of illumination is at its smallest, so that the Northern Hemisphere has the least amount of light, and the longest nights. The far northern lattitudes get no light at all. After the winter solstice, the light returns. This is why the winter solstice is traditionally celebrated as, "the return of the light."

 
 

Because the Earth and the Follow Camera are changing angles relative to the Sun, the Earth's Pole looks appears to be wobbling. But when you look at the scene from the North Pole, you see that the pole is holding steady (unless, of course, you did not align properly).

The effect of this apparent movement of the Earth's poles is that the angle of light falling on each of the hemispheres varies from north to south. As the winter solstice approaches, the light on the Northern Hemisphere shines at a longer and longer angle. As summer solstice approaches, the angle of light in the North becomes shorter and shorter.

 
 

You can see that seasons are opposite is true in the Southern Hemisphere: when the angle and amount of light is shorter in the North, it is longer and greater in the South. When it is summer in one, it is winter in the other. Spring and fall are opposed as well:

 
 

Because the light is more direct during the summer months, less light bounces off the surface of the Earth, and more heat is absorbed. In the winter months, more light bounces off the surface, and less heat is absorbed. During the summer when the length of day is longer, each hemisphere also has more time to absorb the sun's rays. This, then, is what causes the seasons: the cyclical variation in the amount of energy that each hemisphere absorbs from the sun.

For more information on how the angle of light affects reflection and absorption, do a search on the term angle of incidence.

Next: Visualizing the Apparent Motion of the Sun