How to See Where Lunar X Marks the Spot on a First Quarter Moon

The Moon is waxing now, culminating in a full micromoon at the end of this month. This is the opposite of a supermoon; a micromoon is a full Moon at its most distant location from Earth. Though brand-new crescents and glittering full Moons get the most attention, there’s something especially interesting to see this week, when our satellite is half-lit by the Sun. On Friday, Feb. 16, the Moon is at first quarter, and this month, the phase gives us a rare opportunity to see weird phenomena caused by the Moon’s dramatic experience of sunlight and darkness: Lunar X and V.

We see a lot of things when we look up at the Moon. In the Western Hemisphere, people sometimes perceive a face; discussions of this phenomenon date at least to antiquity, most famously a philosophical treatise by the Roman historian Plutarch, called “On the Apparent Face In the Orb of the Moon.” In the Eastern Hemisphere and in some Indigenous American cultures, people see the long ears and face of a rabbit. The Moon Hare is a prominent legend in most Asian cultures, and is the starring character of the Mid-Autumn Festival in China, Japan, and Korea.

It’s not surprising that we would attribute meaning, or even personas, to the Moon’s surface features. Our highly social species evolved to be so focused on faces, and to read the emotion in them, that sometimes we see faces in a random, faceless object—like a wall socket appearing as a startled face. This is called face pareidolia, and almost all of us experience it at some point. Neuroscientists working with functional MRI data have shown that the same areas of our brains used for understanding social information also activate when we experience face pareidolia. Discerning faces where there are none is just one type of pareidolia, the phenomenon of seeing something meaningful in a neutral object or stimuli, such as a butterfly in an inkblot—or maybe a rabbit in the Moon.

Examples of pareidolia are not limited to living things. This Friday, the play of shadow and light on the half-full Moon will reveal two very distinct letters from the Phoenician alphabet, the likely ancestor of all Western alphabets.

First look for the half-lit Moon, in the southwestern sky around sunset. Though it is half illuminated, we call this phase first quarter, because a growing half-Moon is actually the first one-fourth of a full lunar cycle.

Once you find the Moon, locate the terminator, which is the technical name for the line separating sunlight from darkness on a planet or moon. You can see this sometimes at sunset, depending on your vantage point, including elevation. I live on the eastern face of a mountain, so I am lucky to be able to see the solar terminator almost every day: Although the mountains hide the Sun from me by the early afternoon, the plains to my east, beyond the mountain’s shadow, are still bathed in sunlight, and I can see the line between sunlight and shade advancing across our planet. If you were standing on the Moon, the boundary would be even sharper. There is no air, no humidity, to refract any of the Sun’s light, so shadows are extreme and sharply defined.

That brings us to where X marks the spot.

On Friday, notice the Moon’s terminator, and then look to its south pole. Here’s where you will need some good binoculars or a telescope. Train your eyepiece about one-third of the way up from the south pole, along the terminator, and you will see a bright letter X. Now look to the Moon’s north pole, and then drag your eyes downward to see a bright letter V.

This effect only happens a few times a year, when the Moon’s orientation to the Sun and the Earth form shadows in just the right pattern. The X is formed from sunlight hitting the rims of three craters: Purbach, La Caille, and Blanchinus. The V comes from the rim of a crater called Ukert.

The phenomenon is called clair-obscur, a French version of chiaroscuro, a word from Baroque Italian art. It literally means light-dark, and in astronomy it describes the dramatic change between darkness and light on the Moon, creating the illusion of meaningful shapes.

The Lunar X and Lunar V will begin to show up by around 5:30 p.m. Eastern time on Feb. 16, and will peak in intensity by around 7 p.m. Eastern.

If you don’t have binoculars, or you can’t find the X and the V, you can use the Moon’s position to find other shapes in the sky this weekend. The first quarter Moon is sandwiched between the constellation Orion, to its left, and the asterism called the Pleiades, also known as the Seven Sisters or Subaru. This is not a constellation per se, because it does not form a character or a creature—but it is in the shoulder of Taurus the bull, who is confronting Orion. To find this celestial alignment, look to the southwest at twilight. The Moon will orient you. Now look for Orion’s belt of three stars, the easiest way to find the constellation, on the Moon’s “left” side, closer to the eastern horizon. To the “right” of the Moon, further west, you should be able to make out the Pleiades, to which someone, some time long ago, attached the symbolism of seven sisters.

We derive meaning from neutral stimuli all the time. The night sky is one of the best places to find them.

Wondersky columnist Rebecca Boyle is the author of Our Moon: How Earth’s Celestial Companion Transformed the Planet, Guided Evolution, and Made Us Who We Are (January 2024, Random House).