The week of December 9-15. takes us from Day 12 to Day 18. This week we will highlight the craters Wargentin, Nasmyth & Phocylides plus the Geminid meteor shower.

Moon craters Nasmyth, Phocylides and WargentinWargentin: [SW/P4] (Depending on libration, you may have to wait until tomorrow night to see Wargentin.) This is one of the more unusual craters on the Moon. When you catch Wargentin in the right light, it has a fascinating story to tell. There is an almost inviolable rule that crater floors must be lower than their surrounding terrain. Not so with Wargentin! Unlike most crater impacts that leave obvious depressions, the projectile that created Wargentin blasted out a large hole, then opened up cracks that pierced through to the molten zone far below. Subsequently, hot lava rose through these fissures, filled Wargentin’s empty bowl to the brim, then inexplicably stopped just before spilling over!

Wargentin crater on the moonIf the Sun is at a low enough angle, the wrinkle ridge pattern on the surface of Wargentin looks as if an enormous chicken stamped its foot on the ground and flew off just as the lava congealed, leaving its imprint to tantalize the imagination of future astronomers.

Nasmyth/Phocylides: [SW/P-Q4] While you’re in the neighborhood of Wargentin, take a look at its two neighbors to the south, Nasmyth and Phocylides (nayz’ myth; foh-sil’-ih-deez). Under the right lighting conditions they look remarkably like a boot print (probably in hot pursuit of the chicken that just flew off from Wargentin).


The Geminid meteor shower peaks on Friday, December 14, and it is frequently the most spectacular shower of the year with the possibility of 120 meteors per hour! Unfortunately the bright Moon will cut the number down considerably, but there are many very bright and colorful Geminids which will cut through the glare. Look for its peak after midnight.



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 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]

Courtesy of Gray Photography of Corpus Christi, Texas
Lunar photos: NASA / USGS / BMDO / LROC / ASU / DLR / LOLA / Moon Globe. Used by permission

Andrew Planck
Geminid Meteor Shower and Moon Craters Wargentin, Nasmyth and Phocylides

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