Grey clouds skewer the crescent moon around 8:30 Monday night. Photo: Bob King
I caught sight of the thick crescent moon last night just before a mass of grey cloud covered it for good. Our weather tonight looks much more promising for moonwatching although you’ll still need to get out before about 9 p.m. Much later than that and expect to stand on your tippytoes to see it above the treeline.
About two outstretched fists to the left of the moon, Scorpius’ brightest star Antares will become visible by mid-twilight. It’s nodding off in the west these nights as Sagittarius and Capricornus move in to take over the southern sky. Like kings, queens, presidents and prime ministers, every constellation’s dominance is only temporary. Eventually they all move west with the changing seasons and disappear from view.
The moon will be a shiny half-pie Tuesday night in the southwestern sky. You’ll find Antares about two fists to the east. Because the moon is traveling a low arc in the west this time of year, it’s best to observe it before the end of twilight. Created with Stellarium.
Tonight the moon’s terminator, that gently-curved arc that separates the bright, illuminated portion of the moon from the part still in darkness, slices straight across a spectacular trio of craters: Theophilus, Cyrillus and Catherina. The crater rims will glow brilliantly in the early morning sun with bowls still partly steeped in shadow. The terminator is the sunrise line on the waxing moon so anything near it will cast dramatic shadows just as trees and houses do at sunrise here on Earth. The contrast between light and shadow should be strong enough for you to see the crater Theophilus and perhaps the entire trio in a pair of 10 power binoculars. Give it a try and see for yourself. Through a small telescope the chain is one of my top ten coolest spots on the moon.
The striking crater chain of Theophilus, Cyrillus and Catharina will be near the lunar terminator tonight. If you’re clouded out, the next two nights should still provide a fine view. Photo: Bob King
Theophilus is named after an ancient Greek geographer and measures 68 miles across. It fairly fresh as lunar craters go, with a sharp-edged rim and a couple of distinctive central mountain peaks. Theophilus overlaps the much older Cyrillus, which is 61 miles across and named for a 4th century theologian. Scientists determine relative crater age by looking at which craters overlap others (the ones on top are younger) and noting how worn or broken their rims are. Cyrillus’s rim is worn down and much less crisp than Theophilus to the north. The final crater is the chain, Catherina, named for St. Catherine, a Greek theologian and philosopher, is 62 miles across and even more beaten down than Cyrillus.
So we have a neat sequence of craters tonight that show the march of time in the early history of the moon. If you have a telescope, explore the entire moon to see if you can find other craters which hint of their age by appearance and overlap.
Theophilus up close and personal from the window of the Apollo 16 command module. Can you spot Cyrillus and Catharina above and to the right? Credit: NASA