Winter Solstice 2012, On Friday, the northern half of our planet is tilted as far away from the sun as it gets, and the sun appears to hang extremely low in the sky at noon.
The reason for the season is axial tilt. The Earth doesn’t spin around an axis that points straight up and down relative to its orbit; it rotates on a bit of an incline, with the North Pole pretty much constantly pointing towards the north star, Polaris. Axial tilt means that during certain parts of our orbit around the sun, the Northern Hemisphere is tipped more towards Earth than the Southern Hemisphere, making it summer for half the planet; then, in another part of the cycle, we’re tilted back away from the sun.
Winter solstice coincides with the longest night of the year.
“But that’s a good thing!” astronomer Phil Plait wrote for Slate on Friday. “Every day for the next six months, we’ll slowly round the Sun and have our axis point more toward it. The Sun will get higher, the days longer and warmer.”