In addition to rotating on its axis, the Earth also travels around the sun in a path called an orbit. The motion around the sun along its orbit is called a revolution. The amount of time it takes for a single trip around the sun is called a period of revolution. The period for the Earth to revolve around the sun is 365.24 days or one year. The .24 days is why every four years February has 29 days.

Earth's orbit is not a perfect circle. Instead Earth's orbit is slightly elliptical in shape. The animation below shows the Earth's revolution around the sun.

solaranim.gif (19253 bytes)

Source: Earth on Revolution Around the Sun, Palomar College

Image shows the Earth titled on is axis. The North Pole is titled toward the sunlight on the right.

Source: Earth on its Axis, Department of Astronomy and Astrophysics, Penn State University

A common misconception many people have is that the seasons are caused by the distance of the Earth from the sun. This is not true. Because Earth's orbit around the sun is slightly elliptical, Earth is actually slightly closer to the sun in the winter than it is in the summer.

Remember that in section 2 of this lesson we discussed that Earth's axis was tilted about 23.5 degrees. It is the tilt of Earth's axis that causes the seasons.

The following diagram shows Earth's revolution during different times of the year. Pay close attention to the direction of the Earth's titled axis.

Image shows the north Pole titled toward the sun on June 21 and away from the sun on December 21

An imaginary line, the equator, runs horizontally around the center of the Earth dividing Earth into two hemispheres. The area above the equator is referred to as the Northern Hemisphere while the area below the equator is called the Southern Hemisphere.

Image shows the Earth with the equator in the middle and the Northern Hemisphere above the equator and the Southern Hemisphere below the equator

Source: Earth with the Equator, Cburnett, Wikispaces

described in text.

Texas is in the Northern Hemisphere. During our summer we have warmer temperatures and longer days because the Northern Hemisphere is tilted toward the sun and receives more solar energy. However, the Southern Hemisphere has colder temperatures and shorter days because it is tilted away from the sun. This would be the Southern Hemisphere's winter

described in text.

When the Northern Hemisphere is tilted away from the sun, we experience winter in Texas. The temperatures are lower and the days are shorter because we are receiving less solar energy. However the Southern Hemisphere is tilted toward the sun causing higher temperatures and longer days. This would be the Southern Hemisphere's summer.

Check your understanding.

During what months does Australia have summer?

Check Your Answer

Australia is located in the Southern Hemisphere which experiences summer when Earth is tilted toward the sun. The Southern Hemisphere is tilted toward the sun December - February. Close Pop Up