The earth is closer to the sun in the winter than the summer

Most people are surprised to learn that in the summer the Earth is much farther from the Sun than in the winter.  Earth's orbit around the Sun in not perfectly circular, it forms a slight ellipse.  Perihelion, the Earth's closest approach to the Sun, occurs on January 3.  Aphelion, the point at which the Earth is farthest from the Sun, occurs on July 4, often one of the hottest days of the year.  In fact, in January the Earth is about 3,125,000 million miles closer to the Sun than in summer.
 
So why is summer hot?  Shouldn't we have icicles hanging from our noses because we're so far away from the Sun?
 
On some planets, you would.  But Earth's equator is tilted from the ecliptic (the imaginary plane in which all the planets' orbits rotate).  This makes all the difference.  Outside the tropics and the polar regions, what we call "seasons" is the result of a temperature oscillation between an (average) single maximum and a single minimum.  This oscillation results from the annual variation in the angle at which the Sun's rays reach the Earth's surface and from the annual variation in the duration of sunlight on the Earth surface each day.  As the Earth moves in its orbit, its axis maintains a nearly constant orientation in space, inclined about 66°33' to the orbital plane.  During the six-month half of each orbit when the North Pole is inclined towards the Sun, a point in the Northern Hemisphere receives the Sun's rays at a angle closer to 90° than does a point in the Southern Hemisphere; this causes greater heating and more hours of daylight in the Northern Hemisphere than in the Southern Hemisphere.  During the other six months, the conditions are reversed.


There are other factors that influence the average temperature locally, such as the reflectivity (albedo) of different parts of the earth, the greenhouse effect of types of cloud cover, etc, but these factors are de minimus relative to the angle of incidence of the Sun's rays and the duration of that incidence.