California Wild Spring 2003

The Magazine of the CALIFORNIA ACADEMY OF SCIENCES

Skyguide

April - June 2003

Bing F. Quock

April 1: New Moon at 12:24 p.m.––too close to sunset for the crescent moon to be seen this evening. Look tomorrow night.

April 6: Reset clocks one hour ahead (“Spring forward, Fall back”), as most of the United States goes to Daylight Time at 2 a.m.

April 16: Full Moon––only a day before perigee (the Moon’s closest approach to Earth), this is the largest Full Moon of the year and results in very high tides.

April 22: Peak of the Lyrid meteor shower, usually averaging a meager 10–15 meteors per hour. This is the earliest-recorded shower, with Chinese observations dating back to 687 BC.

May 1: New Moon––since most months are longer than the Moon’s 29 1/2-day cycle, whatever Moon phase occurs on the first day of the month will be repeated at the end of the month. Tonight, a razor-thin 15-hour-old crescent may be visible in the twilight just after sunset.

May 15: Full Moon a half-day after perigee once again results in high tides. A total lunar eclipse occurs at moonrise for skywatchers in San Francisco. During an “eclipse season,” which happens about every six months, an eclipse of the Moon will fall within two weeks of an eclipse of the Sun.

May 30: New (Blue) Moon for the second time this month.An annular solar eclipse will be seen along a wide path from Northern Scotland westward to central Greenland. From there, the Moon will move in front of the Sun, but being near apogee (its farthest from Earth), it will appear slightly smaller and won’t block the entire solar disk. The bright ring of the Sun's disk will remain visible like the edge of a penny peeking out from behind a dime. The eclipse will be partial over most of Europe (except Spain and Portugal), the Middle East, Russia, northeast China, Alaska and northwestern Canada.

June 14: In contrast to the Sun, the Full Moon nearest the Summer Solstice follows a low arc across the sky. Tonight, it’s never higher than 30 degrees above the horizon, as seen from San Francisco.

June 21: Summer Solstice at 12:10 p.m.

June 29: New Moon at 11:39 a.m. Binoculars may be needed to glimpse a razor-thin crescent just after sunset.

	Sunrise	Local Noon	Sunset
April 1	5:55 a.m. PST	12:14 p.m. PST	6:32 p.m. PST
May 1	6:14 a.m. PDT	1:07 p.m. PDT	8:00 p.m. PDT
June 1	5:49 a.m. PDT	1:08 p.m. PDT	8:26 p.m. PDT
July 1	5:51 a.m. PDT	1:13 p.m. PDT	8:36 p.m. PDT

Times are for San Francisco, CA, and will vary for other locations.

Mercury In April, the closest planet to the Sun makes its best appearance of the year for northern hemisphere observers. It becomes visible in the west after sunset early in the month. Find it just to the right of the crescent Moon on April 2. Mercury reaches its greatest angular separation from the Sun (eastern elongation) by mid-month, setting about two hours after the Sun, then quickly darts back down into the glow of twilight by the end of April. On May 7, Mercury is at inferior conjunction, meaning that it comes between Earth and the Sun. Later in May, Mercury emerges in the predawn eastern sky in conjunction with brilliant Venus on May 28. On the morning of May 29, Mercury, Venus, and the waning crescent Moon cluster together very low in the east-northeast about 30 minutes before dawn. A closer conjunction of Mercury and Venus occurs very low in the east-northeast on the morning of June 20.

Venus Venus is a morning object this season, visible before dawn. The Moon is nearby on the morning of April 28, with both against the stars of Pisces. On May 29, Venus is joined by tiny, elusive Mercury, with the waning crescent Moon just to the left, all just within the border of Aries. The Moon swings by again on the morning of June 28, when both are in Taurus but so near the Sun that they’ll be difficult to see 30 minutes before dawn.

Mars The Red Planet’s movement eastward against the constellations keeps pace with the Sun’s location. Mars is consistently due south at sunrise this season, slowly moving from the stars of Sagittarius through Capricornus and into Aquarius. The Moon swings nearby on April 23, May 21, and June 19. On June 19, binoculars may reveal faint, greenish Uranus about 3 degrees––or 6 Moon-diameters––above Mars.

Jupiter The giant of the solar system’s planets begins the season very high in the east. At sunset, it’s almost overhead against the stars of Cancer. Moving very slowly against the stars, it manages to edge closer toward Leo by the end of June. By this time, it has crossed over into the west and will be descending toward the Sun by sunset.

Saturn The planet Saturn––which lumbers along even more slowly than Jupiter––barely budges from between the horns of Taurus this season. In April, it’s quite high in the west at sunset. But through May and June, it’s closer to the horizon, gradually dropping toward the Sun and disappearing into the glare by early June in conjunction with the Sun on June 24. The Moon swings near Saturn on the evenings of April 7, May 4, and June 1.

Red Moon Rising

A total lunar eclipse occurs when the Full Moon slips through the red-colored shadow of Earth. This is possible about every six months, and the next opportunity for observers in San Francisco is the evening of May 15. The eclipse begins at 7:03 p.m., before moonrise. By the time the Moon appears at 8:06 p.m. in the east-southeast, it will be almost completely eclipsed. Totality––when the Moon is completely immersed in Earth’s shadow and appears reddish-orange to rusty-brown––is at 8:14 p.m., just 8 minutes or so after moonrise, and lasts until 9:07 p.m., with the Moon only about 10 degrees above the horizon. The partial eclipse, with the Moon on the way out of the shadow, ends at 10:17 p.m., with the Moon 18 degrees high in the southeast. Note the curved edge of the Earth’s shadow in this part of the eclipse. If you track the Moon’s position against the stars throughout the eclipse, you will notice that it moves from west to east by its own diameter each hour. So even though the Earth’s ruddy shadow appears to be sliding onto the Moon from east to west, it’s the Moon that’s actually doing the moving.

Bing F. Quock is assistant chairman of the Morrison Planetarium.