A while back, I wrote about the “just right” conditions necessary for the formation of fog. That particular post discussed the scattering of light, which is done by materials such as titanium dioxide (the principal pigment in white paint) and clouds (where water droplets do the scattering). The birds are chirping at sunrise and the vernal equinox has already passed, which means the sun is finally in the Northern Hemisphere and the days are getting longer and warmer—and all of this points to the beginning of another building season. That got me to thinking about a few other “just right” conditions that seem pertinent for this time of year. And, once again, water comes into play. Continue reading
The Autumnal Equinox is upon us. OK, we know that this means that there are equal amounts of daylight and nighttime. We know that winter is coming to the Northern Hemisphere and that summer is coming to the Southern Hemisphere. But there are other Fun Sun Facts worth mentioning.
At the risk of sounding like a geocentrist, it is easier to describe the movement of the Sun as if the Earth were stationary and the Sun revolved around it. On the Autumnal Equinox, the sun is directly above the equator for this day. If you were standing on the equator at the Equinox, at noon, you would see no shadows, since the sun is directly overhead. The same thing happens on the Vernal (Spring) Equinox. If you want to check this out yourself, catch a flight to Quito, Ecuador, which is right on the equator. The official name of Ecuador, by the way, is the República del Ecuador, which translates into “Republic of the Equator.”
The sun is now making its visit to the southern Hemisphere, and has been doing so since the Summer Solstice (June 22 this year), that day when the sun is as far north as it ever travels. Its “equator” that day is the 23.5°N latitude, also called the Tropic of Cancer. Six months later the sun is as far south as it goes, and—you guessed it—the “equator” on that day, the Winter Solstice (December 21), is 23.5°S latitude, the Tropic of Capricorn.
These Solstice days make for interesting times in those communities lying at or above the Arctic Circle 66°N latitude. On the Summer Solstice, they receive 24 hours of daylight; the Winter Solstice brings them 24 hours of darkness. Here is a good representation of the Sun and the Earth on the Summer Solstice.