The Fabled Green Flash, Liquidambar Trees, and Jupiter-Mercury-Venus and the Moon in the Southwestern Sky

Liquidambar Trees, or sweet gums, the colorfully deciduous trees gracing front yards, parks, and campuses throughout the San Diego area, have been putting on a good show for the past month. The maplelike leaves of most varieties have turned from green to purple to red; the leaves of other varieties have faded to a golden yellow. Other varieties may hold on to their leaves until January. Most liquidambars will regain their foliage by late February.

The Fabled "Green Flash" at sunset or sunrise can sometimes be seen on crystal-clear days in December and January. At the instant the sun's upper rim is last visible at sunset, and also at the instant when it is first seen at sunrise, a flash of emerald-green color may be observed, especially on a flat horizon. Physicists explain this peculiar phenomenon as due to color-dispersion (as in a prism) and scattering of sunlight through the earth's atmosphere. Binoculars (or a small telescope) are helpful in spotting it. For green-flash hunting at sunset, any site with a view of the ocean horizon suffices. For the sunrise green flash, any spot overlooking the low desert (Sunrise Highway in the Laguna Mountains, for example) is good.

The Planet Venus is this season's holiday star. In this, the last week of the calendar year, Venus blazes like crazy in the southwestern sky after dusk, and doesn't set until three hours after the sun does. Venus's tenure as a so-called "evening star" will not last. By next summer, Venus will have "switched sides" relative to the sun, and will appear in the eastern sky at dawn.

The Year Closes with a picturesque arrangement of the moon and three planets in the southwestern sky at dusk. Jupiter (bright) and Mercury (much dimmer) lie within about two degrees of each other low in the sky, while Venus appears much higher and to the left of the Jupiter/Mercury pair. The crescent moon drifts from the vicinity of Jupiter and Mercury on Sunday, December 28 to near Venus on Tuesday, December 30.


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