Five planets, not counting the one we stand on, are visible to the un-aided eye, and all of them may be seen in the night skies of April. During the first half of the month elusive Mercury makes its best evening appearance of the year and a moonless sky affords the opportunity for coastal residents to enjoy a phenomenon unseen by inhabitants of heavily populated areas.
Evening starsOf all the planets to grace the evening sky, the real "star" of the show is Venus, the first object to appear gleaming over the western horizon after sunset. For two weeks, until around April 15 the evening star shares top billing with a co-star, the swiftly moving planet Mercury. From our earthly view, this smallest of all planets never strays far from the sun and seldom climbs high enough to be easily seen. A rare spring evening appearance changes all that.
The spring ecliptic, rising straight out of the western horizon, provides Mercury the path to climb high into the sky by April 9, joining stunning Venus where both will hang in the sky long after sunset and encroaching darkness. As the inner most planet circles the sun it will move into the sun's glare by mid-month, passing between our closest star and earth. On April 15, use binoculars to scan just above sunset for a glimpse of Mercury joined by a very thin crescent moon.
Zodiacal lightFor the first 2 moonless weeks of April keep an eye on the darkening evening sky for a common but usually unseen phenomenon. The ecliptic is a path for much more than the sun, moon and planets. Throughout the solar system, along this path lie countless micrometeoroidal particles, like a vast, wispy cloud of unsettled dust left by the formation of the solar system. For one or two hours after sunset the sun's light scatters in the dust and a hazy, pillar shaped cloud appears, stretching from the western horizon high into the sky slanting toward the left. Because the glow lies along the zodiac, we call it the zodiacal light.
Two conditions improve our chances to see this phenomenon and coastal residents have the best opportunity of all. Any light-glow from a populated area that lies between the observer and western horizon will spoil the view. A trip to the beach after sunset solves that problem. The zodiacal light is visible all year, but is best seen in the evening sky during spring, when the ecliptic and zodiac climb high above the horizon, and in the dark morning sky of autumn.
Late April sightsThe moon returns to the sky for the second half of April, but not to spoil the parade of planets or the first good meteor shower of the year. Saturn climbs from the eastern horizon as the sun sets in the west and, together with the constellation Leo, slowly traverses the sky throughout the night.
Mars, although fading every month, is still the brightest object in the constellation Cancer. From April 13 through 18 the reddish planet will pass very close to the open star cluster M-44, the Beehive cluster. Binoculars will catch both in one view.
Observers who prefer the morning hours may revel in the streaking of from 15 to 20 meteors per hour radiating from the summer constellation of Lyra April 22, long after the glow of the moon has set. Lyra will lie directly overhead at 4 a.m.
The last great sight of an April night occurs just before sunrise, as mighty Jupiter makes its appearance over the eastern horizon.
Bob Duke is a local amateur astronomer, astronomy educator and weekly contributor to The Daily Astorian