The Sky This Week, 2013 April 16 - 23
Lunar Terminator at First Quarter, 2012 March 31
The Moon brightens the evening sky as she waxes through her late crescent and gibbous phases. First Quarter occurs on the 18th at 8:31 am Eastern Daylight Time. Look for Luna less than two degrees above the star Alhena, which marks the "foot" of Gemini twin Pollux, on the evening of the 16th. On the 20th she lies just over five degrees south of Regulus, the heart of Leo, the Lion. By the week’s end she’s drawing a bead on Spica, brightest star of the constellation Virgo. The Moon will pass very close to the star early next week.
Forty one years ago today I had the privilege of watching the penultimate Apollo mission depart the Earth for the Moon. Apollo 16 thundered off the launch pad on a cloudless Florida day destined for the area of the Moon known as Descartes. My view from the press site will forever be engraved in my memory as the amazing power of the Saturn-V rocket outshone the Sun and shook the Earth below me. Days later I rushed between the television in the living room and my telescope as John Young and Charlie Duke explored the crater-pocked landscape they landed on. I have been looking at the Moon at almost every opportunity since then. Somehow, knowing that a dozen of our species have walked on its distant ancient surface has only added to the mystique that has enthralled telescopic observers since the time of Galileo. This is the perfect week for you to get to know our nearest neighbor in space as a place rather than just a bright light in the sky. The Moon is an ideal object to explore with the most modest of instruments. Even a simple pair of binoculars will reveal craters and mountain ranges, and each increase in aperture of a telescope will show ever more details. While it is impossible to see the evidence of our first tentative exploratory steps in any Earthbound telescope, somehow the view of the Moon for me is different knowing that we have actually been there. As Luna’s phase increases over the course of the week you can see an astonishing variety of landforms come into view as the sunrise terminator slowly crawls across the landscape. With a bit of practice you can identify many of the Moon’s more prominent landmarks, and a good lunar atlas will help you pinpoint the six areas that we humans have explored. We often say that the Moon is "looked over, then overlooked" by amateur astronomers, but for many of us it is an enthralling place to visit each month. Take the time to give Luna a look this week, and you may make a new friend for life.
The brightening Moon washes out the dark background of the sky that holds countless remote galaxies in the late evening sky. However, there are a number of bright objects that await your discovery during these brighter nights. We’ll get to the week’s planets in a few moments, but nights with bright Moonlight are perfect for chasing down double stars. Two of the year’s best doubles are in prime observing position now. The first is Mizar, the star that lies at the "bend" in the "handle" of the Big Dipper. Keen eyes or binoculars will show a faint star next to Mizar, but training a telescope on Mizar itself will show a close pair of blue-white stars that slowly orbit each other in a centuries-long dance. Another prominent double is the star Algieba, which lies about eight degrees north of the bright star Regulus in Leo. Point a small telescope toward Algieba and you’ll be rewarded with a fine pair of golden suns suspended in the dark field of view. There are hundreds of other interesting doubles in the springtime sky, so when you tire of looking at the Moon see how many you can track down.
The early evening sky still hosts Jupiter, but the giant planet’s time in the limelight is rapidly drawing to a close. It is now difficult to get a decent view of his turbulent clouds as he settles into the denser layers of air over the western horizon, but you can still easily follow the antics of his four bright moons. He’s not quite done with his evening show yet, though. A month from now he will be part of a spectacular grouping with Venus and Mercury!
Saturn is now just under two weeks away from opposition. You’ll find the ringed planet rising in the southeast at around 8:30 pm, and he’s in good position to observe by 11:00. You should be able to see his famous rings in almost any telescope, and each increase in aperture will reveal more detain in the rings and several of his small icy moons. Pay particular attention to the contrast between the rings and the planet’s disk right now. When opposition occurs you may see a dramatic difference! We’ll have more on the so-called "opposition effect" next week.