Earth revolves around the sun roughly once every 365 days, which sets the length of the year and drives the cycle of the seasons. A slight variance in Earth's average distance from the sun also exists, giving the planet a slightly elliptical path that makes seasons in the Southern Hemisphere somewhat more extreme than those in the Northern Hemisphere.
Earth is tilted somewhat on its axis, which causes first one, then the other, hemisphere to receive more sunlight at different times of the year. When a hemisphere is inclined toward the sun, its days are longer and more sunlight is absorbed. This is what causes summer. Earth is at its closest approach to the sun while the Southern Hemisphere is thus inclined, giving southern latitudes more solar energy in the summer and less in the winter than equivalent northern latitudes.
Earth's revolution around the sun has also had an effect on science. Earth's orbit has a diameter of around 186 million miles, providing a large baseline for measuring the parallax of nearby stars and helping to calibrate their distances. The planet's revolution has also been used to calculate the speed of light by the observation of Jupiter and its moons at various distances.