Bob McPhail 12:30 p.m., April 26
A Crescent Moon and Jupiter Watch Over Grunion Runs
The heat of summer, grunion runs, a slender crescent moon, and Jupiter
The heat of summer will most likely reach its feverish peak in inland San Diego County during the month of July. (Coastal San Diego is different: since its weather is greatly affected by the slowly warming mass of ocean water adjacent to it, coastal temperatures usually peak in August or September.) The weather station at Borrego Springs commonly measures midsummer highs in the 110s Fahrenheit (the record high is 122°, a reading set on June 25, 1990), but certain locales in the low-lying, barren basins of Anza-Borrego Desert State Park -- notably the Borrego and Carrizo badlands -- probably experience even higher temperatures. Overnight camping in the desert in summer is relatively carefree -- little or no shelter is needed and early-morning temperatures are delightfully tepid. Prospective explorers of the desert in summer should take along enormous quantities of water and inform a responsible person of their whereabouts.
Grunion runs in early July are most likely to occur after midnight on the holiday-weekend dates of July 4-6. This corresponds to 1-2 hours after highest nocturnal tide, 2-5 days after the date of the early-July new moon. The small, silvery grunion tend to spawn on wide, gently sloping beaches such as Silver Strand, Mission Beach, Pacific Beach, La Jolla Shores, and Del Mar. California law allows the taking of grunion in summer by those possessing a state fishing license. The grunion must be caught by the hands only, and should be eaten (not wasted).
A slender crescent moon briefly embellishes the western sky during the Independence Day evening twilight, stealing just a bit of attention from the fireworks displays. This and every July 4 is astronomically notable for the fact that it marks Earth's aphelion --the time when our planet lies farthest from the sun (94.5 million miles.) In January, Earth is an almost insignificant three percent closer to the sun than it is now. On account of this minor irregularity, Northern Hemisphere summers tend to be slightly cooler than they otherwise would be. At the same time, the Southern Hemisphere, which experiences winter during our "summer" months, has winters that tend to be slightly cooler.
Jupiter, the brilliant, star-like object glowing like a beacon in the eastern sky after nightfall, comes to "opposition" (180° away from the sun) on July 8. Rising at sunset and setting at sunrise, the giant planet is as close and as bright as it will get this year. Jupiter can be recognized not only by its exceptional brilliance, but also by its tendency not to twinkle as much as the other stars do. Jupiter's light, which emanates from a tiny "disk" (as opposed to a pinpoint) in the sky, is less susceptible to optical distortions when passing through Earth's atmosphere. Generally speaking, any planet seen in the sky twinkles much less than any stars appearing in the same part of the sky.
More like this:
- Low Tides, a Waxing Crescent Moon, and Jupiter's Satellites — Oct. 7, 2010
- July Heat and a Crescent Moon — July 13, 2010
- Grunion Runs Under a Crescent Moon — May 13, 2010
- The Fabled Green Flash, Liquidambar Trees, and Jupiter-Mercury-Venus and the Moon in the Southwestern Sky — Dec. 23, 2008
- Low Tides, Grunion, Crescent Moon, Dawn Sky — July 30, 2008