April 2017 Waning Gibbous Moon Shows Mare Humorum in Lunar Southwest

Summary: The April 2017 waning gibbous moon, which phases between the full and last quarter moons, shows Mare Humorum in the lunar southwest.

Mare Humorum in lunar southwest: USGS Astrogeology Science Center, Public Domain, via Wikimedia Commons

The 2017 waning gibbous moon, which phases between Tuesday, April 11’s full moon and Wednesday, April 19’s last quarter moon, shows Mare Humorum in the lunar southwest quadrant.

Mare Humorum, which translates as “Sea of Moisture,” occupies the near side of the moon. As a lunar mare, the small, nearly circular Mare Humorum, with a diameter of 419.67 kilometers (260.77 miles), actually is a dark basaltic plain originating in ancient volcanic eruptions. The plains, termed maria in the plural, dominate the moon’s northwest and southwest quadrants.

Also in the lunar southwest, Mare Nubium (“Sea of Clouds”) is sited to the east of Mare Humorum. Small Mare Cognitum (“Sea That Has Become Known”) is located northeast of Mare Humorum and northwest of Mare Nubium.

The vast Oceanus Procellarum (“Ocean of Storms”), which stretches from the lunar northwest quadrant southward into the southwest quadrant, lies north of Mare Humorum. Primarily occupying the northwest quadrant, Mare Insularum (“Sea of Islands”) minimally crosses the lunar equator and lies northeast of Mare Humorum.

Mare Humorum’s location in the lunar southwest invites further exploration via binocular, naked eye and telescopic astronomy. In addition to the waning gibbous moon, other lunar phases affording visibility in the Northern Hemisphere include full, waxing gibbous and last quarter. In the Southern Hemisphere, with opposite portions illuminated, Mare Humorum encourages observation during such phases as first quarter, full, and gibbous.

Mare Humorum has a center latitude of minus 24.48 degrees south and a center longitude of minus 38.57 degrees west, according to the International Astronomical Union's (IAU) Gazetter of Planetary Nomenclature. The small lava plain has a northernmost latitudinal reach of minus 18.44 degrees south and a southernmost latitudinal reach of minus 31.06 degrees south. Its easternmost longitudinal reach registers minus 30.61 degrees west, and its westernmost longitudinal extent is minus 45.83 degrees west.

Gassendi Crater dominates the northern edge of Mare Humorum. Inundation by lava has created extremes in the heights of the circular crater’s walls. According to amateur astronomer Peter Grego (1965-2016), some portions of Gassendi’s walls attain a height of 3,600 meters (11,811.02 feet). The southern rim is dramatically lower. The complexly floored crater has a diameter of 111.39 kilometers (69.21 miles). Gassendi Crater honors southeastern France’s priestly astronomer Pierre Gassendi (Jan. 22, 1592-Oct. 24, 1655).

A trio of lava-flooded, partially submerged craters hugs Mare Humorum’s eastern border. Northernmost Agatharchides has a diameter of 51.98 kilometers (32.298 miles). The crater’s damaged outer wall displays considerable height variations, ranging from surface level to 1,500 meters (4,921.26 feet). The resurfaced crater honors Agatharchides of Cnidus, a Greek geographer and historian who lived in the second century BCE in Caria, a region of western Anatolia colonized by the Dorian ethnic group of Classical Greece.

Loewy lies south-southwest of Agatharchides. Lewy’s eroded, worn rim has an elongation toward the southeast and a break in the southwest. Its not quite circular formation measures a diameter of 22.45 kilometers (13.949 miles). The small crater commemorates French astronomer Maurice Loewy (April 15, 1833-Oct. 15, 1907).

Hippalus Crater lies southeast of Loewy. Lacking its southwestern rim, crescent-shaped Hippalus forms a bay in the inner shoreline of Mare Humorum’s eastern edge. The lunar crater remnant has a diameter of 57.36 kilometers (35.64 miles). Hippalus Crater memorializes a Greek merchant and navigator of the first century BCE. Hippalus has been credited with discovering the southwest summer monsoon and/or direct passage from the Red Sea to the Indian subcontinent by way of the Indian Ocean.

As a naked eye feature in the lunar near side’s southwest quadrant, Mare Humorum maintains interest via a diversity of adjacent and nearby landforms. Rilles, which are channel-like grooves in the lunar surface, impressively scar Mare Humorum’s western edge. Promontorium Kelvin rises to a height of 2,000 meters (6,561.68 feet) above Mare Humorum’s eastern plains.

The takeaway for the April 2017 waning gibbous moon’s showing of Mare Humorum in the lunar southwest is the ever deepening familiarity with the Sea of Moisture and its environs via binocular, naked eye and telescopic astronomy.

lunar near side’s major craters and maria: Peter Freiman (Cmglee), Gregory H. Revera (background photography), CC BY SA 3.0, via Wikimedia Commons

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

Mare Humorum in lunar southwest: USGS Astrogeology Science Center, Public Domain, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:GassendiCraterLOC.jpg?uselang=de

lunar near side’s major craters and maria: Peter Freiman (Cmglee), Gregory H. Revera (background photography), CC BY SA 3.0, via Wikimedia Commons @ https://commons.wikimedia.org/wiki/File:Moon_names.svg

For further information:

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