365 Days of the Moon -- August 15, 2014

Aristarchus and Kepler rays, Marius Hills

Here we will take another look at crater rays. Relatively young Kepler (middle right) is only 19 miles in diameter, but its ray system makes quite a splash. Aristarchus at the upper left has a prominent ray system of its own, but in this image it is close to the terminator. Since ray material is mostly small glassy material formed in the heat of crater formation, it is very efficient at reflecting light back toward its source, which of course is the sun. Low sun illumination therefore suppresses ray visibility, so Aristarchus' rays do not fully show their glory here. At full moon, the earth is aligned between the Moon and sun, and the ray's are brightest. Together with giant Copernicus, just out of view at the top, Kepler and Aristarchus form a ray triad on upper Oceanus Procellarum that is a delight to view at moderate telescopic power.

An added bonus in this image is a good look at the volcanic Aristarchus plateau and Schroter's Valley at upper left and the fascinating Marius Hills at the left. The plateau built up from extended volcanic eruptions while the Marius Hills are composed of dozens of small individual volcanic mounds.

Image taken through a Celestron 11 Edge HD and a Skyris 274M camera.

Image copyright Robert Reeves 2014

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