Thursday, May 23 2013 10:49 AM EDT2013-05-23 14:49:05 GMT
During the dry spells of recent years, many Alabamians became familiar with the yellow and red warning indicators of the weekly U.S. Drought Monitor map printed in newspapers and shown on TV weather reports.More >>
Alabama Drought Management Plan outlines for the first time state government's role in preparing the weekly snapshots of current drought conditions, and it specifies steps to be taken in response to potential drought conditions. More >>
Wednesday, May 22 2013 11:14 PM EDT2013-05-23 03:14:08 GMT
It's that time of year again when our attention shifts from the spring threat of thunderstorms and tornadoes to summer's meteorological menace, hurricanes. The Atlantic hurricane season runs from JuneMore >>
It's that time of year again when our attention shifts from the spring threat of thunderstorms and tornadoes to summer's meteorological menace, hurricanes. The Atlantic hurricane season runs from June through November. Every April, Colorado State University releases a preseason forecast, and not everyone is a fan of those predictions.More >>
Wednesday, May 22 2013 2:14 AM EDT2013-05-22 06:14:07 GMT
As reports emerge from Moore, Oklahoma, that nation has learned that schools caught the full impact of Monday's EF-5 tornado.Alabamians have also seen their share of devastation. Eight students died atMore >>
Tuesday, reporter Karen Church investigated how Alabama's newest schools, like Concord Elementary, are being designed to save lives. More >>
The Enhanced Fujita Scale is used by meteorologists to rate the strength of a tornado. More >>
The Enhanced Fujita Scale is used by meteorologists to rate the strength of a tornado.More >>
BATON ROUGE, LA (WAFB) -
Wednesday, March 20 at 6:02 AM (CDT) – we officially kick-off spring! Wednesday is the Spring (Vernal) Equinox, which means 12 hours of daylight and 12 hours of dark, right? Well, not exactly.
If it's called the equinox: why do the sunrise/sunset tables show a few minutes more daylight on the Equinox than exactly 12 hours? Which means "nighttime" is less than 12 hours. The presumption that Equinox means exactly "12-and-12" is based on astronomical geometry (the relationship between the Earth and Sun), and it would be essentially correct if there were no atmosphere.
First off, this "12-and-12" rule ignores the indirect sunlight we get before sunrise and after sunset -- the period officially referred to as "twilight." And twilight is a result of sunlight "scattered" by the atmosphere even when the solar disk is below the horizon. (The moon, for example, with no atmosphere, has no twilight periods.) In fact, there are three types of twilight -- Civil Twilight, Nautical Twilight and Astronomical Twilight -- each effectively defined by the amount of indirect lighting available. (We'll leave it to you to dig up the details of these three definitions.)
But even if we exclude "twilight," the daylight period during the Equinoxes (Remember, there are two each year: Spring/Vernal and Fall/Autumnal) is longer than 12 hours. There are two basic reasons.
First, since the Sun is a "disk" and not a simply a point in the sky, the official "12-and-12" would occur when the solar disk was evenly split through the middle while "sitting" on each horizon -- in the morning and the evening. But the official definition of sunrise/sunset is the time when the upper edge of the solar disk just touches the horizon in the morning as it "rises" and when the upper sits level with the flat horizon as it "sets" in the evening. The time it takes for the Sun to "move" from the solar mid-point to the upper edge (relative to the horizon) adds a couple of minutes to the official "daylight" period at the start and the end of the day.
Second, the Earth's atmosphere refracts (bends) the Sun's direct-beam light (the light from the solar disk). Because of the refraction, we actually see the top edge of the solar disk before that edge has actually risen above the horizon (from a purely geometric perspective). So sunrise "appears" before it would actually occur if there were no atmosphere. Likewise in the evening, atmospheric refraction keeps the solar disk above the horizon a little longer, delaying the time when the solar disk would disappear from view without the atmosphere's refractive effect.
For Baton Rouge, the combination of these two factors extends the daylight period (excluding twilight) about 8 minutes or so -- not exactly something to get all that worked up about, eh? But changing the rules just the same. The added daylight time (still measured in a handful of minutes) gets a little a shorter as you get closer to the equator and a little longer as you move towards the poles.