Winter Solstice 2018
For the Northern Hemisphere, the first day of winter, also called the Winter Solstice, occurs on Friday, December 21 at 5:23 pm Eastern Time. At that precise moment, the north pole of Earth’s axis of rotation will be tilting directly away from the sun. Every day, at local noon, the sun reaches its highest position in the sky for that day. But at the Winter Solstice, that highest position is the lowest (i.e., farthest south, celestially) for the entire year, and we receive the shortest amount of daylight. The sunlight that we do get this time of year is diluted because it’s spread over a larger area, the same way a flashlight beam looks dimmer when you shine it obliquely at a wall.
Fewer hours and weaker sunlight both translate into less received solar energy (insolation) and therefore colder temperatures! Good news for us, though - after Friday, our days start growing longer again! For our friends in the Southern Hemisphere, the Sun will attain its highest noon-time height for the year on the solstice, and it marks the start of their summer season.
It is NOT the case, as some people think, that we are colder in winter because we are farther from the Sun (a position called aphelion). That event happens every year in early July! On the contrary – we’re approaching Earth’s nearest position from the Sun (perihelion), which occurs every January 4, or thereabouts.
Some people think that Christmas was deliberately placed close to the solstice, and Easter placed close to the Vernal Equinox, because early non-Christian “pagans” were already holding celebrations to mark the astronomical changing of the seasons.
Have a Happy Solstice and a Merry Perihelion!