The week of March 16-22 takes us from Day 28 to Day 4. This week we will highlight the Sea of Crises, visible on Sunday night close to the terminator.
Mare Crisium: [NE/H15; L=59°E] On Day 3 the Sea of Crises, the first of the large seas to become visible on the waxing Moon, has now been fully revealed. We tend to think of moon craters as comparatively small objects and lose sight of the fact that large lunar “seas” are the result of crater impacts also. Basically, if it’s round, it’s a crater. Mare Crisium resulted from the impact of a large meteor 3.9 billion years ago. The event was energetic enough to leave a multi-ring imprint, parts of which we can clearly see. Notice the ring features bending around Crisium on its north side. Particularly notice how Mare Anguis on the N.E. side of Crisium [G16] extends itself toward the west, passes below Cleomedes, and then dissipates at Tisserand. The Crisium basin appears elliptical, with its long axis running from north to south. This is an illusion due to the effects of foreshortening. Crisium actually is elliptical, but, contrary to what your eyes tell you, its long axis runs east to west.
Take a mental image of how much space there is between Mare Crisium and the eastern rim of the lunar disk. This will vary from month to month, even from night to night, and will be an indicator of how much libration has come into play. Once you have become familiar with the details on the surface of Mare Crisium, particularly around Promontorium Agarum, be on the lookout for LTP’s. These have been reported from time to time and manifest themselves as mists that mysteriously appear and obscure some of the surrounding details.
If you have the Moon Globe HD app, you can see the effects of foreshortening for yourself. Do a search for Mare Crisium as it normally appears near the east limb of the Moon. Notice how it is elongated north to south. Then with one finger, move Crisium to the center of the screen and it will develop its true east-west elongation.
OF ADDITIONAL INTEREST IN SPACE
On Tuesday, Mercury is 2° north of the Moon and Mars is 1.5° south.
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It is highly recommended that you get a copy of Sky and Telescope’s Field Map of the Moon, the very finest Moon map available for use at the telescope. It is available for $10.95 at www.skyandtelescope.com and on Amazon. All features mentioned in this blog will be keyed to the grid on the Field Map and will look like this: Plato: [NW/D9]
Credits:
Courtesy of Gray Photography of Corpus Christi, Texas
Lunar photos: NASA / USGS / BMDO / LROC / ASU / DLR / LOLA / Moon Globe. Used by permission
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