The sky in April

Natural History, April, 2003 by Joe Rao

Mercury climbs progressively higher above the western horizon every evening at dusk in the first half of the month, but the improving view is offset by the planet's fading brilliance. On the 1st the planet shines at magnitude -1.4; about thirty minutes after sunset, it is very low above the west-northwestern horizon. On the following evening the Moon--visible as an exceedingly thin sliver--hovers about 4 degrees below and to the left of Mercury. On the 16th the planet reaches its greatest elongation (20 degrees east of the Sun) and appears noticeably higher in the sky, but shines more dimly, at magnitude 0.2. For the rest of the month Mercury sinks back down to the horizon while fading rapidly, and is out of sight well before the end of April.

Venus rises like clockwork about an hour before the Sun all month. The planet lingers low in the eastern predawn sky.

Mars--god of war--glares ever more fiercely at the Earth. The pumpkin-colored planet rises in the southeast about four hours before the Sun and nearly reaches culmination by sunrise. Mars is one magnitude, or roughly two-and-a-half times, brighter now than it was on January 1. If your daily routine this month rouses you while the sky is still fairly dark, look to the southeast to watch the planet brighten over April's course from magnitude 0.5 to magnitude 0. At midmonth it stands just 104 million miles from Earth. The planet leaves the constellation Sagittarius, the archer, for Capricorn, the sea goat, on the 21st.

Lordly Jupiter, high in the southern sky at dusk on the 1st, descends toward the west. It starts the month just to the east of the Beehive star cluster, near the center of the faint zodiacal constellation Cancer, the crab. On the 3rd, Jupiter reverses its retrograde, or westward, motion among the stars and begins moving slowly east, away from the Beehive. The waxing gibbous Moon slowly approaches Jupiter from the west--falling for another of Jupiter's famed seductions--in the overnight hours between the 10th and the 11th.

Saturn rides the constellation Taurus, the bull, into April. The planet is readily visible, shining pale yellow at magnitude 0 in the west-northwestern sky during the first half of each night of the month. On April 7, the same night a fat crescent Moon glides well above Saturn, the Earth will finally attain its maximum Saturnicentric latitude. Translation: Saturn's ring system will list at its greatest possible angle toward the Earth, 27 degrees--making for a stunning, brilliant display even through the lens of a small telescope. The last such event took place in September 1988, and the next one isn't due until October 2017. The rings appear to hide the north end of the planet, and stick out a bit behind the south end. Don't miss it!

The Moon is new on the 1st at 2:19 P.M., Eastern Standard Time. It reaches first quarter on the 9th at 7:40 P.M., waxes full on the 16th at 3:36 P.M., and wanes to last quarter on the 23rd at 8:18 A.M. Our satellite reaches perigee at 1:00 A.M. on the 17th, orbiting just 221,937 miles from Earth. Beachcombers, take note. Very high tides can be expected from the coincidence of perigee with the full Moon--a phenomenon known as an astronomical spring tide.

"Spring ahead" in much of Canada and the United States, as daylight saving time returns on Sunday, the 6th. Remember to set clocks ahead one hour.

Unless otherwise noted, all times are given in Eastern Daylight Time.