After the winter we've had, spring is here! Astronomical spring occurs today, but will spring like weather accompany the new season?
It's here! Spring! Astronomical spring arrives on Friday at 6:45pm, the vernal equinox.
And how welcome the season is after such a cold and snowy February. Unfortunately, Spring doesn't necessarily bring with it milder temperatures. The average high today is 59F but it appears temperatures today won't get out of the 40s!
The equinox occurs at the point when the sun crosses the celestial equator from South to North. The image above and below help to visualize this.
At the equinox, the geometric center of the Sun crosses the equator and this point is above the horizon for 12 hours everywhere on Earth. Now when we think about the equinox, we often think about equal hours of daylight and darkness. The word equinox comes from the Latin word "aequus" meaning "equal" and "nox" meaning "night". Although it's close, there are actually a few more minutes of daylight on the equinox than darkness. Monday we had 12 hours of daylight and 12 hours of darkness. Sunrise on Monday, March 17, 2012 was 7:16 AM and sunset was at 7:17 PM. So you may be asking, why wasn't Monday the equinox?
Well, it all comes down to that exact point when the center of the sun crosses the equator. Sunrise and sunset occur when the top of the sun, not the center, is on the horizon. That's why there are actually a few more minutes of daylight on the equinox. Also, the earth's atmosphere refracts, or bends, light from the sun. So, the top of the sun appears to be above the horizon when it is actually below the horizon.
Today (Friday) we'll have a little over 12 hours of daylight (12 hours and 8 minutes), whereas Tuesday had 12 hours of daylight and darkness. From here on out, up until the summer solstice, we'll gain 2 hours 44 minutes of daylight.
The growing daylight and higher sun angle help promote warmer days. Unfortunately, it can sometimes be a slow process in these transition months. Case in point, this March. The average high for the middle of March is about 55°. By the end of the month, the average high will be 61°. The extended forecast starts out seasonable and then get a little warmer than average; however, another dip in temperatures for early next week.