Friday, February 19, 2010

It's Still Cold...But the Sun's Coming Back!

Even though winter drags on,  I'm always intrigued by the changes in the Sun that foretell the coming of Spring.  You may have noticed that the days are getting longer quickly and that the Sun (when it's not blocked by clouds!) is warmer and more intense than it's been in months.  I've had to reset the timers on the lights in my house a few times already, and I've noticed that when my car sits in the sun it warms up inside - a little anyway - even when it's cold outside.
In the weeks before and after the vernal equinox (around 3/21) the Sun's apparent motion among the stars brings it quickly from south to north across the celestial equator.  The result is a rapid lengthening of the daylight period, and a noon sun that climbs higher in the sky each day.
The charts below were made with a year's worth of sunrise and sunset data for White Plains, NY provided by the US Naval Observatory.

On the chart above (click it for a larger view), notice that from mid February through most of April, the days lengthen by more than 2.5 minutes a day.  And notice too, that the daylight period is long from late May through the the first weeks of August.
The chart below is derived from the same data, and shows the longest and shortest days as well as the earliest and latest sunrises and sunsets of the year.
If you want to play around with the data, it's here in an Excel spreadsheet.

No comments: