The rotates on it's tilted axis once every 24 hours, causing day and night.

The earth makes one complete revolution around the sun every 365.25 days.

During the year, the seasons change depending on the amount of sunlight, or solar radiation, reaching the Earth as it revolves around the Sun. The seasons are caused as the Earth, tilted on its axis, travels in a loop around the Sun each year. Summer, or summer solstice, happens in the hemisphere tilted towards the Sun. This is when incoming solar radiation is greatest in the Northern hemisphere. Because of the tilt of the earth, days are longer in the summer giving the sun more time to impact the amount of heat received by the earth. Winter happens in the hemisphere tilted away from the Sun; days are shorter and solar radiations is weak in the northern hemisphere, but great in the Southern Hemisphere. As the Earth travels around the Sun, the hemisphere that is tilted towards or away from the Sun changes, thus, so does the season.

The image at the top is summer because the tilt of the earth is pointing toward the sun. Therefore, days will be longer and the amount of solar radiation will be greatest.

The image at the bottom represents winter because the earth is tilted away from the sun. This will cause shorted days of sunlight and hence, less amounts of incoming solar radiation.