December 28-30, 2025: After sunset, the waxing gibbous moon moves eastward past Aries and toward the Pleiades. Learn what “gibbous” means, how to spot Aries’ stars, and when the moon approaches the Pleaides cluster.
by Jeffrey L. Hunt
Evening Moon
After sundown, the bright gibbous moon passes Aries and moves toward Taurus’ Pleiades star cluster, where the lunar orb occults (eclipses) the stellar bunch for sky watchers across northwestern North America and Asia.
The gibbous moon is waxing — when the moon appears farther eastward after sunset and more of the lunar surface is illuminated. When the phase lies between half-full (First Quarter) and Full, it is named gibbous.
What’s a Gibbous Moon?
The word gibbous comes from the Latin gibbosus, meaning humped or bulging, which itself comes from gibbus, a hump or swelling. In classical and scientific Latin, the word described a convex shape that is not symmetric. This maps cleanly onto the lunar phase: the illuminated portion bulges beyond half, but the disk is not evenly lit. Using the word’s original meaning, this phase can be described as a waxing humped moon.
Aries, the Ram, is west of the bright star fields of Taurus and Gemini. The constellation’s stick figure is formed by three stars — Hamal, Sheratan, and Mesarthim — although the constellation covers a larger patch of sky filled with additional stars. A constellation is defined by the region of sky it occupies, the star pattern used as a guide, and the artwork representing the mythological figure.
The meanings of the stars’ names (from George A. Davis) are:
- Hamal: the full-grown lamb;
- Sheratan: the two signs;
- Mesarthim: the extremely fat ram.
Hamal is over 9° north of the ecliptic, far enough away that the moon never occults it and the bright planets do not pass closely. It is about the same brightness as the stars of the Big Dipper. In suburban settings, and with the moonlight of this waxing humped moon, use a binocular to see the three stars, which span only 5.2° and easily fit into the same binocular field of view.
Sky Highlights
Here’s what to see one hour after sunset:
- December 28: The gibbous moon, 63% illuminated, is nearly 60° above the south-southeast horizon and nearly 30° to Saturn’s upper left. It is less than 20° to Hamal’s lower right.
- December 29: The 74% illuminated moon is over halfway up in the east-southeast, 6.4° to Hamal’s lower right.
- December 30: The lunar orb, 84% illuminated, is over halfway up in the east-southeast, nearly 15° to Hamal’s lower left. It is over 8° to the right of the Pleiades star cluster. Use a binocular to spot the stellar bundle. During the night, the moon approaches the Pleiades for sky watchers across most of North America, but the cluster sets before the occultation occurs.
After sundown, look for the gibbous moon as it appears farther eastward each night, passing Aries and closing in on the Pleiades star cluster.
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