Autumn Arrives
Autumn arrives in the northern hemisphere tonight, as the Sun crosses the equator on its journey southward. Autumn officially begins at 11:03 p.m. Central Daylight Time -- the moment of the September equinox.
The equinoxes and solstices represent the start of the seasons as measured astronomically. At the solstices, the Sun is farthest north or south in the sky for the year. And at the equinoxes, it's half-way between. The Sun rises due east and sets due west on the equinoxes across the entire globe -- the only times of year for which that's true. And day and night are of roughly equal length on the equinoxes.
There are many other ways to calculate the seasons, though. For families, the seasons revolve around the school calendar. Here in Texas, for example, "summer" ended during the scorching days of mid-August, when the new school year began. And on the meteorological calendar, autumn began on September 1st.
In many societies, a solstice or equinox represented not the start of a season, but its mid-point. In these cultures, today would be the middle of autumn, not its beginning. These cultures marked the changing of the seasons on cross-quarter days -- days like Halloweeen or Groundhog Day.
After today, the days in the northern hemisphere will grow shorter, as the Sun moves farther south in our sky. They'll continue getting shorter until after the winter solstice on December 21st -- 90 days from now.
Script by Damond Benningfield, Copyright 2006
For more skywatching tips, astronomy news, and much more, read StarDate magazine.
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