For 2012, January 4th at 5pm Pacific time is the closest approach of the earth to the sun.
I wonder if any part of the Dharma pays any attention to such astronomical events like this.... Kalacakra maybe??
As far as I know, I don't think so, though not entirely sure. Kalacakra astrology, which is pretty much Vedic astrology calculated off a tropical chart (apart from it's connections with Dharma and some other differences) probably pays more attention to things like eclipses than this, which is an annual event that I don't think
has much influence. The next full on solar eclipse is May 20'th 2012. This will particularly shake things up for Geminis. If your moon is in Gemini, for example, it will have a large effect on your emotional life, shaking it to destroy and rebuild on some level, etc. Sun is in Gemini it will shake things up on the level of your personality.
I could be wrong about the perihelion. Perihelions form between the sun and each of the planets (heavenly bodies) once each year. Any time a heavenly body is in the point in it's orbit which is closest to the sun, is called it's perihelion.