Western Slope Skies 5/10/2013

May 10, 2013

“Hey, can you see the flag in that thing?!”  It’s a question that makes us wince when observing the moon at astronomy outreaches.  The answer is…Maybe if you were aboard NASA’s Lunar Reconnaissance Orbiter… but, all six of the flags are now faded to white, and the first one blew over when the Apollo 11 lunar module blasted off departing the moon.  

From our backyards, the moon, our closest celestial neighbor, is easily observed by the unaided eye  as it moves through its changing phases.  During the next two weeks, the moon will move from new to nearly full.


This Saturday, May 11th, as you look to the west, the moon will appear as a thin crescent above the bright planet Venus, and below Jupiter.  This is a good opportunity to see the phenomenon called “earthshine”, caused by sunlight reflecting from the Earth onto the lunar night side, while the sun directly illuminates the crescent.

A week later on May 18th, the moon will be half-lit by the sun at “first quarter” phase, meaning it is one quarter through its 29-day cycle.  At this stage, by using binoculars, the lighter-colored, densely cratered areas called “highlands” will come into view, as well as the darker “Maria” which are large impact basins that became filled with basalt lava-  the same rock that caps Grand Mesa!  Be sure to look along the “terminator”, which is the line between the lit-side and dark portions of the moon.


On May 22, a gibbous, or “more than half, but not full” moon, will appear near the planet Saturn.  If you look at the southern part of the moon with binoculars, you will see the rays of the crater Tycho extending most of the way around the face.  The bright rays are from material that was thrown out of the crater by an asteroid impact 120 million years ago…relatively recent by lunar history standards.

“Western Slope Skies” is produced by members of the Black Canyon Astronomical Society.