Last Friday I photographed a polka festival and enjoyed seeing the pleasure on the couples’ faces as they hopped and turned about the dance floor. A good dance partner adds zest to life. A similar dance on a celestial plane happens tonight when the moon returns to the evening sky alongside Mercury and Venus. Watch for the trio starting about 25 minutes after sunset low in the northwestern sky.
The 2-day-old crescent will be easiest to see; from there hop over to bright Venus and fainter Mercury. You might not see Mercury at first, but if you wait for the sky to darken a little, it will eventually show. In case of haze, take along binoculars to make the finding easy. Through a telescope Venus looks like a tiny gibbous moon while Mercury appears as an teenier half-moon.
The International Astronomical Union, keeper of the names for solar system bodies, recently approved 10 new names for Mercurian cliff-like faults called rupes. Rupes is the Latin word for cliff, and Mercury has an abundance of them. Long ago, as the planet’s core cooled and contracted, the outer crust responded in kind and contracted too. Where does extra crust go on a shrinking planet? Pieces of it are thrust up and over other areas of crust to create escarpments or cliffs. Geologists call these thrust faults; some are are hundreds of miles long and up to 2 miles (3 km) high.
Newly named Enterprise Rupes – the longest – stretches for 510 miles (820 km). In keeping with nomenclature rules, Mercury’s escarpments are named after ships of discovery. The U.S.S. Enterprise was launched on June 13,1874 , its first duty to survey the Mississippi River. Calypso Rupes was named for sea explorer Jacques Cousteau’s ship. To learn more about Mercury’s faults and other features, please visit the Mercury MESSENGER site.
Try to find Mercury soon before it drops back down into the sun’s glare in a week or so. This is the best time of year for northern hemisphere observers to see it in evening skies.