Bob McPhail 9:30 a.m., Sept. 3
Fall Officially Begins
Fall officially begins at 8:44 a.m. Pacific Daylight Time on Monday, September 22 -- a good excuse to throw a "thank-God-it's-Monday-morning" party to celebrate the occasion and kick off the work week. At equinox, the sun shines directly down somewhere on Earth's equator. At 8:44 a.m. San Diego time this year, that equatorial spot lies deep in the Amazon basin. The autumn season will continue for another three months until the sun "moves" to its farthest southerly point, winter solstice, December 21.
Equal days and nights everywhere on earth, 12 hours each, are only one noticeable consequence during the time of equinox, either autumnal or vernal (spring). Another consequence is that the sun at equinox always rises from a point on the horizon due east and later sets due west. You could calibrate a compass this way if you had access to a true (unobstructed) horizon. Another, subtle consequence is that at mid-latitudes like ours, morning and evening twilight periods are shortest during equinox. From San Diego, the duration of twilight this week is about 80 minutes; last June it was about 100 minutes.
Highest tides for September (a not-very-high +5.7 feet), are predicted for 7:17 p.m. on Thursday, the 25th and for 8:04 p.m. on Friday, the 26th. The month's two lowest tides (a not-very-low minus 0.3 feet) will occur on the mornings of the 25th and 26th at 1:19 a.m. and 1:56 a.m., respectively. During September the tidal range is typically minimized. Starting in mid-October, extreme negative tides will begin to occur during the afternoon hours (a much more convenient time for exploring tidepools in the low-lying intertidal zone), and not much in the early morning. By December the highest high tides will crest at about +7 feet and the lowest low tides will sink to nearly -2 feet.
Fall migrant birds such as wood warblers can be seen at Cabrillo National Monument and its vicinity on Point Loma, Torrey Pines State Reserve, and other parks and open spaces near the San Diego coast. Cooper's or marsh hawks and even peregrine falcons may be seen following or pursuing these smaller birds.
More like this:
- The Moon, the Tides, and the Vernal Equinox — March 17, 2011
- The Quadrantid Meteor Shower, Extreme Tides — Jan. 2, 2011
- Fall Officially Begins — Sept. 22, 2010
- Autumn Arrives — Sept. 21, 2009
- Crescent Moon and High Tide on Wednesday, September 16 — Sept. 15, 2009