It has its own interior rimae that is especially prominent to the east and a smashing view of trio Posidonius O, I and B on the north crater rim. Power up to observe the stepped, stadium-like wall structure and numerous resolvable mountain peaks joining its small, central interior crater. However, a telescope is needed to appreciate the many fine features found on Posidonius’ floor. Tonight it will resemble a bright, elliptical pancake on the surface to smaller optics with its ring structure remaining conspicuous to binoculars throughout all lunar phases. Spanning 84 by 98 kilometers, you can plainly see Posidonius is shallow – dropping only 2590 meters below the surface. This huge, old, mountain-walled plain is considered a class V crater and could be as much as 3 billion years old. Almost flat from eons of lava flows, this crater shows numerous variations in texture along its floor in small telescopes. On its northeast shore, binoculars will have no trouble spotting the shallow ring of crater Posidonius. Ma– On the lunar surface tonight, let’s begin with a look at Mare Serenitatus – the “Serene Sea”. Keep the Messiers in mind, for in a few days you will see a pair of “rays” extending out from them. Rima Messier is a long surface crack which runs diagonally across Mare Fecunditatis’ northwestern flank and reaches a length of 100 kilometers. For a challenging telescopic note, you’ll find another point of interest to the northwest. At high power, Messier A to the west appears to have overlapped a smaller crater during its formation and it is slightly larger at 11 by 13 kilometers. The easternmost crater is somewhat oval in shape with dimensions of 9 by 11 kilometers. These twin craters will be difficult in binoculars, but not hard for even a small telescope and intermediate power. Scan along the terminator over Mare Fecunditatis about 1/3 its width from west to east for a pair of emerging bright rings. This is an opportunity to challenge yourself by identifying two small craters just slightly northwest of the mare’s central point – Messier and Messier A – named for the famous French comet hunter – Charles Messier. Now aim towards the earthen shore of Mare Fecunditatus and identify the flat, bright oval of a previous study, Langrenus. They are also bordered by parallel fault lines and are quite similar to such terrestrial features as Death Valley in the western United States. Look closely along the western shore of Fecunditatis where you will see many such graben features. The forces created by lava flow increase the weight inside the basin, causing a tension along the border which eventually fault and cause these areas. On Earth, these happen along tectonic plates, but on the Moon they are found around basins. These down-dropped areas of landscape between parallel fault lines occur where the crust is stretched to the breaking point. Stretching out across an area about equal in size to the state of California, the Sea of Fertility’s western edge is home to features we share terrestrially – grabens. The lower titanium content means it is between 3.1 and 3.6 billion years old. Studies show the basaltic flow inside of the Fecunditatis basin perhaps occurred all at once, making its chemical composition different from other maria. It is home to glasses, pyroxenes, feldspars, oxides, olivines, troilite and metals in its lunar soil, which is called regolith. The combined area of this mare is equal in size to the Great Sandy Desert in Australia-and almost as vacant in interior features. Its expanse covers 1463 kilometers in diameter. Ma– We begin our binocular and small telescope explorations tonight by looking near the center of the lunar terminator to identify and take a closer look at Mare Fecunditatis.
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