Driving west at dusk yesterday evening, all I wanted to do was twist my head around to see the big moon rising behind me. Since that's never a safe move, instead I turned left off the highway and drove down to a nearby beach. In the darkening sky the moon beamed white above Earth's purply shadow.
Although I knew it was one day shy of full, the lunar disk looked convincingly circular. Only later, through the telescope, was I able to see that the slimmest sliver of the western edge was missing, still in shadow. This edge, called the terminator, defines the boundary between day and night on the moon. Lunar features cast shadows that bring mountains and craters into relief here as the sun rises. As long as you can see shading along one edge of the moon it isn't 100% full.
Jan. 28 marks the night of the Full Wolf Moon. Wolves are especially vocal during January and February because it's the peak of their breeding season which happens once a year. If you live in a rural area and the sky is clear tonight, pull your hat up over your ears and listen for them.
The full moon will rise close to sunset in the northeastern sky in the constellation Cancer the Crab. To find your moonrise time, click here. Cancer is a faint pattern of stars sandwiched between two bright constellations — Gemini the Twins and Leo the Lion. One night later, on Friday, Jan. 29, the moon will be slightly less than full and situated about one fist further east (left) in Leo. It moves east because it's orbiting the Earth, making one complete circle around the sky in just under a month.
Since the full moon lies opposite the sun and rises when the sun sets in the west, it follows that on the 29th, the day after full, it will be below the horizon at the time of sunset. But if we wait about an hour, the Earth will rotate the moon back into view. The next night it rises about two hours later because — you guessed it — the moon keeps moving east.
During the winter and spring months, each successive moonrise after full moon is delayed by more than an hour because the moon's path at the horizon is steeply slanted. The hours accumulate so that by Jan. 31 the moon rises more than 3 1/2 hours after sunset. Exactly the opposite happens in the fall during the Harvest Moon. Then its path is nearly parallel with the horizon and successive moonrises happen just 20-30 minutes apart.
But wait, there's more! If you have a 3-inch or larger telescope you can see part of a gigantic lunar bull's-eye called Mare Orientale (Eastern Sea) Thursday through Saturday, Jan. 28-30. Astronomers estimate that an asteroid about 40 miles (64 km) across crashed into the moon around 3.8 billion years ago. The tremendous energy generated in the impact partially liquified the crust. Concentric waves of molten rock spread outward from the epicenter similar to what happens when a drop of water falls into cup of tea and creates a series of expanding ripples.
The rock solidified to form concentric rings of alternating mountain ranges and smoother lava plains in the shape of an enormous bull's-eye 560 miles (900 km) across.
Unfortunately, to see it best you'll need to hop on a spaceship and orbit the moon because most of Mare Orientale is out of view on the lunar far side. But not all of it. At special times, when the moon's western edge is angled our way, the giant basin is visible as a series of narrow dark and bright stripes just inside its edge.
Now is one of those special times. Start at the prominent, dark-floored crater Grimaldi inside the moon's eastern edge. Although Mare Orientale lies at the extreme western edge of the moon from the point of view of someone on the moon, from here on the ground the sky direction is east.
Once you've found Grimaldi, look to its south and east for two dark, spaghetti-like stripes. These are sections of the ring-shaped lava plains that separate the mountain ranges of Mare Orientale. The inner stripe is Lacus Autumni (Lake of Autumn) and the outer is Lacus Veris (Lake of Spring). They thread-like because we view them almost edge-on.
Now look closely at the very edge of the moon below the stripes for a gray, lens-shaped patch. That's Mare Orientale — ground zero! Once you see it I hope that with a little imagination you can picture this amazing formation for what it is.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.