September 22, 2009
The first day of autumn arrives on varying dates in different years for two reasons: Our year is not exactly an even number of days; and Earth's slightly noncircular orbit, plus the gravitational tug of the other planets, constantly changes our planet's orientation to the sun from year to year.
And weather-wise, Earth's seasons have shifted in the past 150 years or so, according to a study that came out earlier this year. The hottest and coldest days of the years now are occurring almost two days earlier.
This year, fall starts Tuesday, because that is when the so-called autumnal equinox occurs (at 5:18 p.m. EDT). Equinoxes (which mark the onset of spring and autumn) and solstices (which mark when summer and winter begin) are points in time and space that mark a transition in our planet's annual trip around the sun.
At each equinox, the sun crosses the Earth's equator, making night and day of approximately equal length on most of the planet (from the Latin, equinox means "equal night"). At the equator, the sun is directly overhead at noon on either equinox.
Happy Autumn!
Today (September 22) marks the beginning of the Autumn season this year, and in Lebanon it has officially began a couple of days ago with the heavy rain we were witnessing. The fi…
Today (September 22) marks the beginning of the Autumn season this year, and in Lebanon it has officially began a couple of days ago with the heavy rain we were witnessing.
The first day of autumn arrives on varying dates in different years for two reasons: Our year is not exactly an even number of days; and Earth's slightly noncircular orbit, plus the gravitational tug of the other planets, constantly changes our planet's orientation to the sun from year to year.
And weather-wise, Earth's seasons have shifted in the past 150 years or so, according to a study that came out earlier this year. The hottest and coldest days of the years now are occurring almost two days earlier.
This year, fall starts Tuesday, because that is when the so-called autumnal equinox occurs (at 5:18 p.m. EDT). Equinoxes (which mark the onset of spring and autumn) and solstices (which mark when summer and winter begin) are points in time and space that mark a transition in our planet's annual trip around the sun.
At each equinox, the sun crosses the Earth's equator, making night and day of approximately equal length on most of the planet (from the Latin, equinox means "equal night"). At the equator, the sun is directly overhead at noon on either equinox.
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