Time to celebrate the Turkey Moon! Wait, there’s no such thing. Tonight’s full moon is the Beaver Moon, named for the month in which beavers prepare for winter. But it should be the Turkey Moon. For two good reasons. First, it occurs on Thanksgiving this year and second, a full moon on Thanksgiving is a rarity. I checked back over the years and discovered that the last time full moon occurred on the holiday was Nov. 25, 1920, nearly a century ago.
There have been a bunch of “almost” full moons the day before or after Thanksgiving or a full moon but only over one time zone. Even tonight’s time of greatest fullness — 11:39 p.m. Central Time — misses the Eastern time zone, but for the majority of the U.S., full moon occurs on Thanksgiving. The next “Turkey Moon” won’t occur until November 27, 2042.
What better way to walk off today’s big meal than putting on a coat and going for a stroll under Earth’s only natural satellite. We’ve grown so used to the moon being around, it’s easy to forget how alien a place it is. As weird and strange as say, Jupiter’s moon Ganymede. A quick look through even a small telescope tonight will reveal big, bright splotches — craters surrounded by rays of secondary impact craters — and expansive dark patches called seas better known as the eyes, nose and mouth of the man in the moon.
Even with the naked eye you can see that most have round shapes and for good reason: they’re enormous impact craters. Astronomers class them as impact basins. Unlike lesser impacts, the asteroids that excavated these giant holes 4.2 to 3.2 billion years ago dug so deeply they tapped into magmas below the crust. Molten rock oozed through cracks in the basins’ floors and filled them up like you’d fill a swimming pool with water.
With essentially no atmosphere, the moon’s temperature typically varies from 260° F (127° C) when the sun’s is high up to 280° F below zero (–173° C) at night. When you look up at the shiny moon tonight, imagine you could boil a pot of tea of there in a minute. Actually, in even less time than that. Because there’s no air pressure, a container of water left in the open would boil away all by itself in a very short time.
I mentioned Ganymede, Jupiter’s largest moon. It’s the largest moon in the solar system at 3,274 miles (5,268 km) across or almost exactly 1.5 times the size of our moon. Ganymede is larger even than the planet Mercury, but because it’s tethered to Jupiter, it’s classified as a moon. Of all the moons in the solar system, to my eye, Ganymede most resembles our moon in general appearance. It has craters, many with bright rays, and a mix of dark- and light-colored regions. The darker terrain is younger — like the lunar seas — and bright areas older. Also like our moon, Ganymede keeps the same face towards toward its host planet.
But there are significant differences. Ganymede is the only moon in the solar system with a magnetic field. Its core is composed of metallic iron surrounded by a layer of rock and encased in a thick crust of ice. Just beneath that crust gurgles a salty ocean. In the upper right portion of the first photo, in a dark region named Galileo Regio, you can see a series of concentric grooves that might have formed from tectonic activity (movement of large parts of Ganymede’s crust) due to gravitational “flexing” by Jupiter. That look flat in the image, but they extend for thousands of miles and can up to reach 2,000 feet high.
If there’s something all our space missions have taught us it’s that each body in the solar system is unique though it’s fun looking for similarities. Just like people.