Earlier Sunsets, Coastal Sage, and a Harvest Moon

The time of sunset changes most rapidly this time of the year. This is mainly because the sun is swinging rapidly south along the ecliptic (its apparent path through the background stars). From the latitude of San Diego, the sun is now setting about 75 seconds earlier every day (equivalent to about 9 minutes earlier per week), and its setting position along the horizon shifts southward about 1/2 degree per day.

San Diego's coastal sage-scrub vegetation is now at the very nadir of its growth cycle. Shades of gray and yellow have replaced the bright greens that carpeted many of the still-wild coastal hillsides up until April or May of this year. Sometime within the next two or three months, the first substantial autumn rain will shatter the usual summer drought, and our "summer-deciduous" vegetation could bounce back in a matter of days.

The full moon on Monday, September 15 rises a little before sunset, while Tuesday's moon rises perhaps even more majestically from the eastern horizon during the deep gloom of twilight. This a perfect time to take a twilight walk on Harbor Island or Shelter Island, or along the west shore of Mission Bay. September's full moon is often called the "harvest moon," because its rising time changes only a little for several consecutive days centered around the day of full moon. During harvest-moon periods of the past, farmers were able to work several late evenings in a row by the unfailing light of the full or nearly full moon. Because weather conditions in September often promote stagnant air and hazy skies, the rising harvest moon often appears pumpkin-like. Its light may be dimmed and filtered while skimming through the atmosphere.


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