Friendly crater Gassendi

Mar 22

Written by:
3/22/2013 6:39 AM  RssIcon

This evening (or any evening of 80% waxing gibbous phase) into the morning hours of the 23-rd, the crater Gassendi will be partially lit along the terminator shadow on the Moon.  It is easy to find; in the southwestern quadrant of the Moon, just off the northern edge of the Mare Humorum.   Small telescopes will easily show this 69 miles (110 km) diameter blasted-out dish on its surface.  With a central peak - or rather, multiple peaks - and a rough appearance in the lava-covered floor, viewing this area tonight into tomorrow will produce some of the best views of this area, and after Plato, is perhaps one of the finer sights on the Moon.  See if you can spot some of the cracks and ridges inside the crater floor.  It was filled with lava long ago, yet unlike many others that have had that occur, Gassendi retains it's entire circular shape.  Despite this - or perhaps because of it - the rim varies in height from just 650 feet (200 m) to as high as 1.6 miles (2.5 km)!

SCROLL DOWN FOR DETAILED GRAPHIC.  For more general lunar observing info, check here.

80 percent lunar phase

A smaller crater intrudes into the main, larger one; this is Gassendi A.  Far smaller at just 20 miles (33 km) across, it may appear stark in contrast due to the shadow inside it covering a larger percentage of the interior.  There are 15 other craters associated with Gassendi, though most of them are small, ranging in size from 1.2 to 7 miles across (2 km to 11 km).  The exception is Gassendi B, located just off the northwestern edge of Gassendi A.  It is 16 miles (26 km) across, and slightly deeper in shadow tonight.  It will be better viewed tomorrow evening.  These craters are named for Pierre Gassendi, a French philospher, priest, scientist, astronomer and mathematician.  Gassendi published the first data on the transit of Mercury that occurred in 1631.    

To the north and east of the Gassendi system, look for Herigonius in Oceanus Procellarum.  At a mere 9 miles (15 km) across and 1.3 miles (2.1 km) deep, it also has a small central peak, which may test your vision and observing conditions.  It was named for French mathematician and astronomer Pierre Hérigone.

This region contains many rilles and other non-crater features; shadows from the low Sun angle may help you observe these more easily on the 22nd and 23rd.  Another area worth checking out is the Montes Jura region off Mare Imbrium (see graphic above).  

Gassendi crater region detail, also Herigonius

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The Nightlight

This blog includes what to see in the night and daytime skies, thoughts on telescopes, binoculars, and other astronomy observing accessories and equipment, plus my own occasional notes on objects I've seen and observed. Oh, and the random theater or other "my take on life" post. In other words, there is always something interesting. Check it out.