The Earth spins on an axis tilted at a 24 degree angle with respect to the sun. In December, the northern end of the axis is tilted away from the sun and in July, the
northern end of the axis is pointed toward the sun. The tilt of the Earth's axis is responsible for two effects. The first changes the length of day as the seasons change. You may be noticing that there are fewer hours of daylight (in November) than there are in July. Shortened days mean that there is less time for the sun to warm the Earth, resulting in cooler temperatures.
The second effect is a little more difficult to understand. The temperature depends on the sun's intensity-that is, on the amount of sunlight on an area. The total amount of sunlight is constant, but the tilt of the Earth changes the angle at which the sunlight hits the Earth's surface. When the surface is perpendicular to the sunlight the area illuminated is smaller than when the sunlight is at an angle.
You can test this by aiming a flashlight at the wall. When you aim the flashlight directly at the wall, you will make a circle of light. If you tilt the flashlight, the spot on the wall will have a greater area, but will be less bright.
When the sun's rays hit the Earth's surface at an angle, the same amount of energy must warm a larger area, and cooler weather results. Because of the position of Lansing and the tilt of the Earth's axis, sunlight has the greatest intensity in July and the least intensity in December.
The combination of longer days and more intense sunlight explains why our summer falls in July and our winter in December.
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