Looking Up April 2012

Daylight hours continue to increase in April, as the Earth spins through spring towards summer. Early in the month (about April 4th) the sun will rise at 6:45 am EDT, and set by 7:36 pm.  Towards the end of the month (about April 20th) the sun will rise at 6:20 am, and set by 7:50 pm.   The moon will be at Full phase on April 4, 3rd quarter on April 13, New on April 21 (a happy circumstance for the Lyrid meteor shower), and 1st quarter on April 29.

On April 2-4 Venus glides past the Pleiades (the Seven Sisters and their parents).  The stars of the Pleiades cluster are only moderately bright (third and fourth magnitude), and brilliant Venus will outshine them by 8 magnitudes.  Closest approach will be April 2nd, when Venus passes less than half a degree the brightest sister Alcyone (for comparison, our Moon is about half a degree wide).  Venus remains the brightest object in the evening sky (barring the Moon), and will be visible for at least 3 hours after sunset every clear evening.   By the end of the month, Venus will appear as a fat crescent, as it moves around the Sun towards inferior conjunction (and transit!) on June 5th.

Mars is the second brightest planet in the evening sky, high over the south-eastern horizon at sunset.  Mars is still in the retrograde phase of it’s dance with Earth, and will spend the entire month hanging out in the constellation Leo near the bright first magnitude star Regulus. Mars is about 3 magnitudes brighter than Regulus, and will be obviously reddish to most people.   The Big Dipper can be used to find Leo and Regulus: first use the Big Dipper’s pointer stars to find Polaris (the North Star), then trace back the opposite direction, across the zenith of the sky (you’ll want to spin around to face South at this point, or you’ll fall over backwards 😉 to the first bright star you come to – that’ll be Regulus – and this year Mars will be right there, too.

Jupiter gradually disappears into the western sunset as the month progresses, while Saturn moves into the evening sky.  Saturn reaches opposition on April 15th, and will be zeroth magnitude.  The rings continue opening from their edge-on appearance in 2009, and this year will be tipped towards Earthly viewers by a full 15 degrees; the maximum  opening of 27 degrees will occur 13 years from now, in 2025.

The Lyrid meteor shower is predicted to peak on April 21, the same date as the New Moon, so there will be no moonlight to wash out the meteor trails.   City lights can definitely wash out meteor trails, so if you’d like a really good view plan to spend your pre-dawn hours as far from street lights and dark-phobic neighbors and car dealerships as you can get.   This shower is usually not too spectacular, with average Zenith rates of only 18 per hour, but the meteors are relatively swift, owing to the Lyrid orbit relative to Earth’s orbit, some can be spectacularly bright, and about 1 in 5 leave a train that persists for several seconds.

That’s all for this month.   And, as the great Jack Horkhemier used to say, Keep Looking Up!

Helen Hart, 19 March 2012; references:  the Astronomical Calendar, Starry Night planetarium program, USNO Astronomical Data Services.

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