Monday, November 04, 2013

Solar Winter Begins Tomorrow

You hear us refer to winter in a couple of different classifications -- meteorological winter, which is the months of December, January, and February; and astronomical winter, which is the season that begins with the winter solstice on December 21st (most years).

There's also a term occasionally thrown around called solar winter, which is the shortest days of the year in a three month timeframe.  For the Northern Hemisphere, that starts tomorrow. In Philadelphia, that means daylight between tomorrow and February 5th will be 10 hours, 20 minutes or shorter over the next 90ish days.  It also yields our lowest sun angles in the sky, with the sun trending between 26 and 34 degrees above the horizon at midday.  This is in contrast to our "solar summer", which occurs from May through August. During that timeframe, the sun is between 66 and almost 74 degrees above the horizon at 1 PM. You'll notice how much more direct sunlight hits you in May, June, July, and August and how much easier it is to burn in that timeframe as opposed to over the next few weeks. Having more direct, intense, and longer duration of sunlight will do that!

Graphic showing the sun's position over Brazil at 11 AM today. The white circle to the sun's east is the approximate position of the moon. Via

The sun's most direct light beams down across the Southern Hemisphere between late September and late March.  For us, lower sun angle means easier chances for cold to build up since the sun can't provide as much solar heating nor provide it for as long a period of time as it does across the Southern Hemisphere over the next several months.

With sunsets now before 5 PM until mid January thanks to the end of daylight saving time, the feeling of very short days and long nights will take hold over the region whether you like it or not. Of course, with the end of daylight saving time the occasional voice in the wilderness calling for time zone reform and/or the end of DST in the United States comes out of the woodwork.