Why is it colder in the winter even though the Earth is closer to the Sun?

Why is it colder in the winter even though the Earth is closer to the Sun?
Top Image: ChaoticMind75 - iStock

Concepts: seasons, axis of rotation

Skills: observing, critical thinking

What you need

  • Lamp (with shade removed)
  • Large ball (an air-filled beach ball is ideal)
  • Marker
  • Drinking straw (cut in half)
  • Plasticine
  • LEGO™ figure or other small object
  • Room that can be made dark

Safety first! Light bulbs can get very hot. Make sure your hands and other objects do not touch the bulb.

What to do

  1. Draw a line around the middle of the ball to represent the Earth’s equator. Stick the opening of one piece of a drinking straw on the ‘North Pole’ using plasticine. The straw should stick out from the surface of the ball at a right angle. Do the same thing with the other piece of drinking straw at the ‘South Pole.’ The drinking straws represent the line of the Earth’s axis.
  2. Stick a LEGO™ figure, or other small object, about 3/4 of the way above the equator to represent someone living in Canada.
  3. Move the ball (Earth) around the lamp (Sun) in a circular motion. This represents the Earth’s orbit. The line you drew on the ball to represent the equator should be at the same level as the lamp’s light bulb.
  4. Next, hold the Earth with its axis (straw at the ‘North Pole’) tilted at about a 20 degree angle towards the Sun on the side where the LEGO™ figure is located. The LEGO™ figure and equator line should be fully lit up by the light bulb. In North America, we call this position relative to the Sun “summer.” To see what day and night is like during the summer, spin the ball around its axis and watch where there is light and shadow on the Earth.
  5. Next, move the Earth over to the opposite side of the light keeping the axis at the same angle as you did for the previous step. Ensure you keep the ‘North Pole’ pointing in the same direction as you did previously. That is, if the ‘North Pole’ was tilted to the left in relation to the Sun, it should still be pointed to the left when moved to the opposite side. This represents 6 months later. Make sure the Earth is slightly closer to the Sun at this point. In North America, we call this position relative to the Sun “winter.” Rotate the Earth so that LEGO™ figure is on the side facing the Sun. Notice where the light and shadow is now. To see what day and night is like during the winter, spin the ball around its axis and watch where there is light and shadow on the Earth.
  6. Complete the year by having the Earth move around the Sun back to the starting (“summer”) position. The Earth should be further from the Sun at this point than it was in its winter position.

Discovery

What's happening?

People often think that it is hotter in the summer (in the northern hemisphere) because the Earth is closer to the Sun. In fact, in the northern hemisphere summer, the Earth is farther away!

The reason for the difference in temperature between the summer and the winter actually has to do with the tilt of the Earth’s axis. If the Earth were not tilted at an angle, there would be no summer or winter.

In the summer, the northern hemisphere is tilted toward the Sun which means that the Sun’s rays hit this part of the Earth’s surface more directly. Since there is more direct sunlight, more of the Sun’s energy is absorbed by the land surface. As a result, the temperature is higher. Depending on where you live in relation to the equator, if you look up towards the Sun at noon (12 p.m.) in the summer, you will see that the Sun is higher in the sky than it is in the winter.

In the winter, the northern hemisphere is tilted away from the Sun, which means that the Sun’s rays hit this part of the Earth in a more oblique or slanted manner. Since there is less direct sunshine, less energy is absorbed by the surface and the temperature is lower. If you look up towards the Sun at noon in the winter, you will see that the Sun lower in the sky.

The southern hemisphere experiences the reverse of the northern hemisphere. When it is summer in the northern hemisphere, it is winter in the southern hemisphere and vice versa. So remember, seasons are all about the tilt of the Earth’s axis, not the distance between the Earth and the Sun!

Why does it matter?

The tilt of the Earth as it travels around the Sun determines our seasons.

Investigate further!

Try the activity again, changing the tilt of your Earth. What would happen if the Earth had no tilt? What if it was tilted at 90°?