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Hello, Autumn! Today is the Fall Equinox

"Autumn is a second spring when every leaf is a flower." —Albert Camus

Autumn is almost here — or has already arrived, depending on how early you're reading Alameda Patch today. This year, fall officially begins in and around San Francisco at 7:49 a.m. PDT on Sept. 22, 2012, according to timeanddate.com.

The autumn equinox occurs, according to the Washington Post, "when the sun crosses the equator and day and night are of roughly equal length, everywhere in the world."

In Alameda, according to sunrisesunset.com, the sun will come up at 6:57 a.m. and set at 7:09 p.m on the autumnal equinox. Why not a perfect 12-hour day?

"The geometric center of the sun is above the horizon for 12 hours, and one might think this would indicate that the length of the day (hours of daylight) would be the same," says timeanddate.com.

"However, ‘sunrise’ is defined as the instant when the upper edge of the sun's disk becomes visible above the horizon — not when the center of the sun is visible. In the same sense, ‘sunset’ refers to the moment the upper edge disappears below the horizon. At both instances, the center of the sun is below the horizon, and therefore the equinox day lasts a little longer than 12 hours."

For gardeners in Alameda, the start of autumn means it's time to set out cool season annuals and plant onions fro seed. For a detailed look at fall gardening chores, see the Alameda County Masters Gardeners' month-by-month guide.

Here's the weekend forecast according to the National Weather Service:

  • Saturday: Early morning fog. Clouds through the morning, with mainly sunny skies in the afternoon. High near 75. Winds between 5 and 10 mph.
  • Saturday Night: Some patchy fog. Low near 58. Winds between 5 and 10 mph.
  • Sunday: Early morning fog. Clouds through the morning, with mainly sunny skies in the afternoon. High near 73. Winds between 5 and 10 mph.
  • Sunday Night: Mostly cloudy, with a low around 58.

Albert Camus quote courtesy of www.brainyquote.com.

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10dB September 22, 2012 at 03:37 PM
Another reason why day and night are not equal at the equinox is that the atmosphere bends the sun's rays. When we see the top of the sun's disk finally slip below the horizon it has actually been below the horizon for several minutes. Kinda nice of nature to give us a few extra minutes of sunlight as we head for the short days of winter. Don't mean to be a pedant about this, but I teach celestial navigation and compensating for atmospheric bending of light (whether the sun, moon, or stars) is an important part of turning a sight into a position on the face of the earth.

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