Oceanus Procellarum: The Moon's Big "Ocean"
You don't need a telescope to see Oceanus Procellarum, the Moon's "ocean of storms". You can see it with your unaided eye each month when the Moon is nearly full and thereafter until the Moon is a thin, waning crescent. Oceanus Procellarum covers around 1.5 million square miles (an area about half the size of the lower 48 United States) and extends some 1,600 miles north to south across the face of the Moon. Recent studies by various spacecraft now suggest that Oceanus Procellarum was formed very early in the Moon's history by volcanism from multiple vents and rift valleys rather than by a big asteroid impact. Oceanus Procellarum evidently was also much wider when it first formed. Maria Imbrium, Serenitatis and Nubium appear to have been created by impacts on top of Oceanus Procellarum.
The image below was taken December 16, 2014 with my Celestron NexStar 6" Schmidt-Cassegrain telescope with an f/6.3 focal reducer to widen the field and a Celestron Neximage 5 Solar System Camera. The image is a stack of the best 10 out of 60 frames processed in Registax 6 and Photoshop Elements 9.
At the northwest (upper left) edge of the image is Sinus Iridum in Mare Imbrium. Southeast of Sinus Iridum and approximately in the center of the image is the bright crater Aristarchus and the Aristarchus Plateau. Aristarchus, at about 450 million years old, is one of the "newer" lunar craters and is often the brightest single feature on the Moon. It is about 25 miles wide and the dominant feature on the Aristarchus Plateau. While the crater was formed by an impact, the plateau itself is largely volcanic and covers over 21,000 square miles, or about twice the size of Massachusetts.
South of Aristarchus and in the center of a large ejecta blanket with ejecta rays spreading in all directions is the 20 mile wide impact crater Kepler. To Kepler's upper left is the 20 mile wide crater T. Mayer. An ejecta ray extending west and very slightly above Kepler points to the shadow filled, 19 mile wide crater Reiner. Just west (right) of Reiner is the mysterious white area Reiner Gamma. This latter area is quite flat and formed of a thin layer of some kind of light material which shines bright when sunlit. Southwest of Kepler near the Moon's west limb is the 143 mile diameter crater Grimaldi. Grimaldi is a largely flat basin filled with dark lava. While Oceanus Procellarum seems to be mostly a large, flat plain, closer examination under higher powers reveals lots more interesting features to explore.
Jay Albert, 3/17/2015