The Sky This Week, 2011 April 5 - 12
The Moon waxes in the evening sky this week, climbing rapidly into the setting constellations o the Great Winter Circle. First Quarter occurs on the 11th at 8:05 am Eastern Daylight Time. Luna’s slender crescent may be seen flanking the Pleiades star cluster on the evenings of the 6th and 7th. On the 9th she stands above the upraised "club" of Orion, the Hunter, and two nights later forms a nearly straight line with Castor and Pollux, the Twin Stars of Gemini.
April is a great month to explore the battered face of our only natural satellite. The geometry of her orbit allows us the chance to see her early crescent phases under very favorable conditions as each night passes. We often sat that the Moon is "looked over, then overlooked" by casual observers, but the changing light as the terminator line progresses across her surface constantly reveals new and intriguing features to even the most seasoned observers. Studying the Moon is something that can be done with virtually any instrument from any location, and offers many of us a chance to take a break from gleaning moments of fleeting detail on a distant planet or trying to make out the faint smudge of light from a remote galaxy. Exploring the Moon is recreational stargazing at its best. The target’s big and bright, it changes from night to night, and it has features which are very easy to become well-acquainted with. I often feel as if I know my way around the Moon better than I do some of the neighborhoods near my home. It’s also a great hook to get kids interested in science. And even though it is one of the most desolate places that we know in the Universe, it’s still the only other place in the Cosmos that we’ve actually visited.
Both Mercury and Jupiter, which, a few short weeks ago, were in the spotlight of the evening twilight hours, pass though conjunction with the Sun this week. Jupiter inches behind Old Sol on the 6th, while Mercury slips between the earth and Sun on the 9th. Both planets will emerge into the morning sky by the end of the month to join Venus and Mars in a rare pre-dawn grouping.
Golden Saturn is now the only planet visible during the overnight hours. The ringed planet reached opposition on the 3rd and now graces the sky from sunset to sunrise. He can be seen in the southeastern sky as twilight fades to darkness about 11 degrees to the northwest of the bright blue star Spica and transits the meridian at around 1:00 am. Saturn’s famous rings are currently tipped about 10 degrees to our line of sight with their northern face visible. This affords us an unobstructed view of the planet’s northern hemisphere, which has played host to a spectacular outbreak of white clouds for the past few months. These clouds are thought to be formed by a huge convective weather complex deep in the planet’s atmosphere analogous to a terrestrial "supercell" thunderstorm, but on a scale that can barely be imagined. The cloud may be seen under favorable conditions in medium-aperture amateur telescopes.
Venus rises about an hour before the Sun in the southeastern twilight sky. The planet’s dazzling brightness assures her visibility as the sky grows brighter, and keen-eyed skywatchers can probably continue to see her for some time after sunrise on very clear mornings.