Happy Perihelion 2012!
Okay, so it’s not a commonly-celebrated event. Nevertheless, January 4th, 2012 is a significant date for the year, at least astronomically. Perihelion occurs on Wednesday, January 4th, 2012. This marks the time when the Earth is closest to the Sun for the year. Yes, I said closest. ‘Peri’ comes from the French for ‘near to,’ and ‘helion’ comes from the Greek for ‘Sun.’
Many people believe, mistakenly, that the Earth is farthest from the Sun in winter. However, we need to realize that when it is winter in the northern hemisphere it is summer in the southern hemisphere, and vice versa.
Earth (and every other planet) orbits the Sun in an elliptical orbit, not in a circular one. So, there will be one moment of the year when the Earth is closest to the Sun and another moment in the year when the Earth is farthest from the Sun. Those moments are known as perihelion and aphelion, respectively; and always occur around January 4th and July 4th, respectively.
The difference in distance from the Sun between these two dates is rather small, around 5 million km, and has little noticeable effect on temperatures.