DJ Stevens 3:30 p.m., Sept. 17
Rainbow Season, Fremont Cottonwoods, Venus & Jupiter, the Moon's Chesire Cat Smile
"Rainbow season" arrives with the first rains of late fall. Scattered showers are best for rainbow watching: sunlight refracting and reflecting through the raindrops causes two bows to appear: an intense circular arc at 42˚, and a bigger, but weaker arc at 51˚ from the antisolar point (the point in the sky diametrically opposed to the sun's position). From November through mid-February, the sun never gets higher than 42˚ above the horizon as seen from San Diego, so (rain and sunlight permitting) the brighter of the two arcs may appear above the horizon at any time of day. In spring and summer, rainbows are never seen in the sky around midday because the sun is too high -- and the antisolar point is too low.
The Fremont cottonwoods along the San Diego River in Mission Gorge are now showing their best tawny foliage. You can park at the Old Mission Dam historic site or the Mission Trails Regional Park visitor center and explore the riparian area by way of riverside trails, or by walking, bike riding, or skating along the bike path high above the river's south and east banks. Large cottonwoods can also be seen along other watercourses throughout the San Diego County backcountry, including along the Sweetwater River near Cottonwood Golf Course, and in Cottonwood Valley, east of Pine Valley along Interstate 8.
The moon's Cheshire-cat smile returns to the evening sky Saturday evening, November 29. You'll spot its thin crescent shape low in the southwest about half an hour after sunset.
Venus and Jupiter, the two brightest planets in the night sky, are just 2 degrees apart low in the southwest at dusk on Sunday evening, November 30. Venus is several times brighter than Jupiter, making the pair resemble mismatched cats' eyes. Adding spice to the scene is the crescent moon, appearing below and to the right of the planetary pair. On the following evening (Monday, December 1), the slightly thicker crescent moon will lie above and to the left of Venus and Jupiter -- creating a glittering triangular arrangement.