Baked into the bones of astronomy is a simple fact: Nothing ever stops moving. Atom hum inside stars, planets and asteroids spin, and the moon barrels headlong along its orbit every minute of the day like a dog running her heart out. For you and I that means we rarely have to wait very long for something interesting to happen. On Thursday, Nov. 11, for instance, you'll find the half-moon in conjunction with Jupiter, 5 degrees to its north, as soon as the sky gets dark.
If you have a telescope, I encourage to aim it moonward and seek the curious crater Cassini, named for the 17th century Italian astronomer Giovanni Cassini. He discovered four moons of Saturn and was the first to see the dark division in Saturn's rings we know as Cassini's Division. On good nights with a 4-inch or larger telescope, it's a delicate black curve separating the outer Ring A from the inner Ring B.
The crater measures 35 miles (57 kilomesters) across and 3,900 feet (1.2 kilometers) deep. While that depth sounds impressive, Cassini used to be much deeper, but lava flows after the massive impact that created the neighboring Sea of Showers (Mare Imbrium) flooded its floor like a swimming pool. Even in a small scope magnifying around 75x its Cassini's interior looks smooth and shallow.
Within its walls are two easy-to-spot, smaller craters, Cassini A (10.5 miles / 17 kilomesters) and B (5.6 miles / 9 kilomesters). Back in 1952, English moon mappers H.P. Wilkins and Patrick Moore likened the basin-shaped Cassini A to a washbowl. The name stuck, and that's what moon-watchers have called it ever since. I've seen it many times over the years and can confirm the impression.
Cassini and the Washbowl are just coming into view in low-slanted sunlight on Nov. 11, a wonderful time to pay the craters a visit. Should bad weather prevail, the crater will still be easy to spot through about Nov. 15. Even a 3-inch telescope will show the trio, but if you have a 6-inch or larger instrument and bump up the magnification to 150x or higher, you'll notice that the Washbowl has a double-stepped appearance. What you're seeing are actually two adjoining craters that formed when a pair of large meteorites struck the moon at the same time.
Astronomers imagine the following scenario from the remote past: An asteroid gets slammed by an impact and produces a multitude of fragments, including a closely-orbiting pair that struck the moon at a later date. An alternative view posits that the duo formed during a single, oblique impact. Isn't the moon amazing? It has tens of thousands of stories there. This is just one of them.
We could spend lots of time exploring other craters, but the moon moves on and so will we. The following night, Nov. 12, it passes just below (south) of the 4th magnitude star Tau-2 Aquarii in the constellation Aquarius. You might see the star in binoculars, but I suspect you'll need a small telescope for a good view. Tau-2 will hover just over the lunar edge from many locations across the U.S. and Canada. From southern Florida the moon will cover or occult the star around 7 p.m. local time, while New Orleanians can watch the star "scrape" along the moon's edge starting around 6 p.m. local time.
The rest of us can use Tau-2 to gauge the moon's eastward orbital motion over a short period of time. The moon orbits the Earth at an average speed of 2,300 mph (3,700 kilometers per second) — dang fast, but often hard to perceive without a good reference. From many locations, the pair will be close together as soon as it gets dark out then slowly separate during the night. You should be able to detect the moon's movement in relation to the star in as little as a half-hour.
Finally, the moon and the most distant planet Neptune buddy up about 5 degrees apart Friday, Nov. 13. Again, I suspect Neptune, at magnitude 7.8, might not be visible in binoculars because of the lunar glare, but I'd love you to prove me wrong. However, even the smallest telescope will show the planet if you use the moon or the nearly triplet of Phi 1-3 Aquarii to star-hop to the planet's location.
The moon is a ship. Get aboard and you'll see some wonderful places.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.