California Wild Spring 2005

The Magazine of the CALIFORNIA ACADEMY OF SCIENCES

Skyguide

April to June 2005

Bing F. Quock

April 3 On the first Sunday in April, most of the United States changes from Standard to Daylight time. Set clocksforward one hour at 2 AM-or, more conveniently,at bedtime on the evening of the 2nd. Clocks are not changed in American Samoa, Hawaii, most of Arizona and Indiana, Puerto Rico, and the Virgin Islands, where Daylight Time is not observed.

April 8 The shadow-path of an annular-total solar eclipse crosses Costa Rica, Colombia, Panama, and Venezuela as the New Moon passes in front of the Sun. Skywatchers in the southern United States will see a partial eclipse. With New Moon at 12:34 PM PDT, the first visible crescent of this phase will not be seen until the following evening, marking the start of the month Rabi-al-Awwal in the Islamic calendar.

April 16 Astronomy Day, observed since 1973 in either April or May on the Saturday closest to the First Quarter Moon. Amateur astronomers will set up information and activity booths in many locations and, weather-permitting, host public star parties in the evening to share their enthusiasm for the oldest science.

April 22 Peak of the Lyrid meteor shower, which usually yields 15-20 meteors per hour. The light of a nearly-full Moon will obscure the view this time around.

April 24 Full Moon, known to the Dakota Sioux as the "Moon when Geese Return in Scattered Formations." A penumbral lunar eclipse occurs when the Moon passes through the faint, outer portion of Earth's shadow. This shadow is so pale that any darkening of the Moon's face is usually visible only in photographs. Observers in California will see the Moon's northwestern edge around 3 AM.

May 5 Peak of the Eta Aquarid meteor shower, one of two showers spawned by Halley's Comet. This display typically produces about 20-30 meteors per hour. The Moon should not interfere with viewing.

May 8 New Moon at 1:48 AM PDT. Look low in the west soon after sunset (8:07 pm) for an 18-hour-old crescent Moon. This marks the beginning of the month Rabi-al-Thani in the Islamic calendar.

May 23 Full Moon. The Nunamiut Eskimos called this the "Moon When the Ice Goes Out of the Rivers," and to the San Ildefonso it was the "Planting Moon."

June 6 New Moon at 2:57 PM PDT--too late to be visible at sunset, but look tomorrow evening, June 7.

June 20 Summer solstice, or beginning of Summer, for the Northern Hemisphere at 11:48 PM PDT. The Sun rises and sets at its most northerly points on the horizon.

June 21 Full Moon. Many Native American tribes (Algonquin, Dakota Sioux) named this Moon after the ripening of berries, while others marked good fishing (Nez Perce, Tlingit) or the growing of corn (Cherokee, Laguna). The Lakota Sioux just summed it all up by calling it the "Moon of Making Fat." Notice that the Full Moon nearest the Summer solstice makes the shortest, lowest arc.

The Planets

Mercury
Mercury makes a fleeting appearance in the predawn sky in April and May, but it's hard to see. Retreating into the Sun's glow by late May, it passes superior conjunction on June 3 and moves into the evening sky, becoming visible before sunset by mid-June. At that time, watch it climb toward brighter Venus, then cluster spectacularly with Venus and Saturn on June 25. On the evening of June 27, it's less than one-tenth of a degree from Venus in the closest planet-to-planet approach this year. The crescent Moon swings close by on the mornings of April 7 and May 6.

Venus
The brightest planet emerges from superior conjunction in early April and can be seen low in the evening sky by mid-May, where it remains through the entire Summer. Don't miss the spectacular clustering of Venus, Mercury, and Saturn in late June.

Mars
The Red Planet is a predawn object, rising against the stars of Capricornus between 3 and 4 am in April, when it's visible low in the southeast just before sunrise. The Moon passes by on April 3, May 2 and 31, and June 28 and 29.

Jupiter
At opposition April 3, the King of the Planets rises at sunset and is visible all night long against the stars of Virgo. Each night afterward, it rises about four minutes earlier and is slightly higher in the sky when it appears each evening. By the end of June, it's high in the south-southwest at sunset. The Moon passes by on the evenings of April 21 and 22, May 18 and 19 (when the two are only a third of a degree apart), and June 15.

Saturn
The magnificent Ringed Planet is very high in the south just after sunset in early April, near the stars Castor and Pollux in Gemini. Through the season, it gradually moves toward the west each nightfall. Watch for it near Venus and Mercury after sunset in late June.

Fourth of July Fireworks—On a Comet

Launched on January 13, NASA's Deep Impact spacecraft is heading for a rendezvous with Comet Tempel 1. This will be one fiery flyby. The spacecraft, or flyby vehicle, carries a suite of observation instruments and an 816-pound, mostly-copper projectile known as the "impactor." It releases the impactor some 300 miles from the comet on July 3 about 24 hours before the planned July 4 encounter. The impactor will take about 35 images of the comet as it approaches from space, sending data back to the flyby vehicle. Then it will slam into the comet's nucleus at a speed of 23,000 miles per hour, or about six miles per second. The energy released is expected to approximate that of five tons of TNT. The impactor is expected to blast out a stadium-sized crater, and may create a flash visible from Earth, where telescope-toting observers will see the comet's faint glow in the constellation Virgo. The ideal viewing spot—aside from being aboard the flyby vehicle 300 miles from the comet—is expected to be Hawaii. There, the two giant Keck telescopes will be observing and analyzing the plume of pulverized comet material created by the impact.

Bing F. Quock is Assistant Chairman of the Morrison Planetarium.