September 222009
First Day of Autumn
Today marks the first day of Autumn. Below is some information I posted a few years back that I thought I’d repost for this occasion.
“Did you ever wonder why leaves change colors in the fall?
A pigment called chlorophyll helps turn water, air and light energy into food for plants. When a plant contains a lot of chlorophyll, it appears green. There are also other pigments present, such as purple, red and yellow, but these colors are masked by the green chlorophyll. During the fall, the production of chlorophyll decreases due to the change in temperature. This is when the other pigments appear, and the leaves display brilliant colors. But this also means that the leaves are reaching the end of their life cycle.
The Autumnal Equinox
The point in late September when the sun appears to cross the celestial equator from north to south marks the beginning of autumn. On this date, the night becomes longer than the day for those of us in the Northern Hemisphere.
Autumn vs. Fall
The word autumn refers to the autumnal equinox that marks the start of the season, but what about fall? An online search indicates people have several theories about where the use of the word fall comes from. Some say its simply because of falling leaves. Others say its a term that started in the South where the word autumn seemed to invoke a colorful season that didnt occur there. It seems that the prevalence of one term over the other follows geography.”
(sources: weather.com, USC)
