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The Sky This Week, 2012 April 3 - 10

Venus dazzles, Mars fades.

Cylindrical projection map of Mars
Based on images captured Feb. - Mar. 2012
with a 20-cm (8-inch) f/10 Schmidt-Cassegrain telescope

The Moon brightens the late evening and early morning sky this week, passing through the springtime constellations as he takes a southerly course toward the rising stars of the summer sky. Full Moon occurs on the 6th at 3:19 pm Eastern Daylight Time. April’s Full Moon is popularly known as the Grass Moon, Egg Moon, or Paschal Moon. As the first Full Moon to fall after the vernal equinox, it fixes the dates of Passover for Jews and Easter for Christians. Luna begins the week to the southeast of Mars, then drifts eastward to pass just two degrees below the bright star Spica on the night of the 6th. Saturn is part of the picture too on this evening, just over five degrees northeast of Spica. Early risers on the morning of the 10th will find the Moon just four degrees north of the red-tinged star Antares, the heart of Scorpius, the Scorpion.

There is no doubt now about which planet dominates the evening sky. Dazzling Venus is now at the peak of her best visibility for this current evening apparition. On clear nights you can easily follow her progress down toward the northwest horizon, where she sets well after 11:30 pm. As bright as she is right now, she will become brighter as the month passes, ultimately reaching a blazing -4.7 magnitude by mid-April. This will be the time to go to a dark-sky location and look for shadows cast by the planet’s light. It is also a great time to test your observing skills to try to locate her in the daytime. I have been able to spot her fairly quickly at around 4:00 pm EDT when she crosses the meridian. To do so I hide the Sun behind a wall or other obstruction, then hold my clenched fist at arm’s length. One such "fist-width" covers about 10 degrees of the sky, so measure four fists from the position of the sun toward the zenith, then relax your eyes and look for a bright, fixed point of light. Once you’ve found it you should have little trouble repeating your sighting. It is not unusual for people to stumble across Venus in the daytime accidentally. I had an astronomy teacher in high school who served on convoy escort duty in World War II. On several occasions he tried to shoot Venus down, mistaking its daytime appearance for a high-flying enemy airplane! On the evening of the 3rd look for Venus to traverse the easternmost stars of the famous Pleiades star cluster. Over the next few nights she’ll leave the Seven Sisters in her dazzling wake.

While Venus continues to climb, Jupiter inexorably sinks toward the advancing Sun. Old Jove starts the week lagging some 17 degrees behind Venus, and by the week’s end he finds himself over 20 degrees from the brilliant planet. The giant planet now sets shortly after the end of evening twilight, so any telescopic viewing will be limited to times when the sky background is still a bit bright. Small telescopes are at an advantage here since they are less subject to the distorting effects of the earth’s atmosphere, but about all you’ll probably be able to see are the small disc of the planet and the four Galilean moons.

Mars is the ruddy object that’s just under 10 degrees above the Moon on the evening of the 3rd. The red planet has faded by half a magnitude from his peak brightness at opposition just a few weeks ago, and his apparent disc is beginning to shrink quite rapidly. Each passing day adds another 4.5 million miles of space between Earth and Mars, and in a few more weeks it will be difficult to discern much detail on his distant face. Fortunately we have a number of robot explorers circling the planet and parked on its surface, and in August the Mars Science Laboratory rover should reach its objective and land softly in a crater named Gale. Even though our direct view of Mars will fade until April 2014 we’ll all have a ringside seat to our continued exploration of this fascinating world.

Saturn meets up with the Moon on the evening of the 6th, almost lost in Luna’s glare. The ringed planet is just over a week away from opposition, and he now beckons for telescopic attention during the later evening hours. The planet’s rings are now tipped 17 degrees to our line of sight, and they haven’t been this "open" to view since early 2007. Saturn should keep us spellbound well into the summer months, staying close to the bright blue star Spica throughout the current apparition.

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