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On Thursday, October 15, 2026, look about an hour after sunset toward the low southwestern sky. A 30-percent-illuminated waxing crescent Moon will be near Scorpius and Sagittarius’ Teapot. A telescope aimed at western Mare Fecunditatis can reveal Messier and Messier A, two nearby craters formed by one impactor that skipped across the Moon. Their most distinctive feature is a long, bright ejecta ray extending westward.
When and where to look
The observing times below are for 40° N, 90° W. Local conditions at another latitude or longitude will shift the Moon’s altitude and timing, so treat them as a planning reference rather than universal times.
| Event | Time or condition |
|---|---|
| Sunrise | 7:11 A.M. |
| Sunset | 6:20 P.M. |
| Moonrise | 12:25 P.M. |
| Moonset | 9:11 P.M. |
| Moon phase | Waxing crescent, 30% illuminated |
Begin roughly one hour after sunset, around 7:20 P.M. at the reference location. The Moon will be low in the southwest, above the back of Scorpius and close to the Teapot shape in Sagittarius. The relatively short window before moonset makes it useful to set up your telescope before twilight ends.
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- Find the Moon. Face southwest after sunset and identify the waxing crescent.
- Use the large lunar landmarks. Through the telescope, locate Mare Crisium, the round, dark plain near the Moon’s eastern side. Mare Fecunditatis lies below it in the view.
- Move to western Mare Fecunditatis. Scan the western portion of this dark plain at moderate magnification.
- Look for the paired craters. Messier is the eastern crater; Messier A is immediately west of it. They are approximately 4 miles (6 kilometers) apart.
- Trace the ejecta ray. A narrow, white, tail-like streak runs westward from the pair and is the easiest feature to confirm that you have found them.
Do you need a telescope?
Yes, if you want to examine the two craters themselves. The Moon and its major maria are visible without optical aid, but Messier and Messier A are small features. A small telescope with a stable mount is the practical minimum for separating the pair and following the bright ray. Increase magnification only after the Moon is centered and sharply focused; excessive power in turbulent air can make the craters harder to distinguish.
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A printed lunar atlas or observing guide can help match Mare Crisium and Mare Fecunditatis to the telescope view. Let your eyes adapt to the bright lunar scene rather than using deep-sky dark adaptation, and avoid looking at the Sun through the telescope at any time.
Why this is a double crater
Messier and Messier A are not thought to be unrelated impacts that happened to land close together. The leading explanation is a single, shallow-angle collision. A comet nucleus or asteroid struck the surface to make Messier, then skipped across the regolith like a stone skipping on water and created Messier A a few miles away.
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The geometry explains the pair’s unusual appearance. The two craters are close enough to be recognized as a set, yet their outlines and depths differ. The impact also produced the prominent westward ejecta ray. Alison Klesman, senior editor of Astronomy magazine, describes it as “This unique pair of craters was created by just one impactor that skipped along the lunar surface, leaving a cometlike tail of ejecta.”
What to compare through the eyepiece
| Feature | Messier | Messier A |
|---|---|---|
| East–west position | East of the pair | West of Messier |
| Relationship | First crater in the proposed skip sequence | Second crater made after the impactor rebounded |
| Shape and depth | Compare directly; it is not identical to Messier A | Compare directly; it is not identical to Messier |
| Surrounding ejecta | A bright, white ray extends westward from the pair | |
Because the Moon’s apparent orientation changes with viewing conditions and telescope design, rely on the surrounding maria and the ray rather than assuming west on the page always matches west in your eyepiece. The east–west relationship remains the key: Messier is on the eastern side and Messier A on the western side.
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Viewing conditions and troubleshooting
- The pair is hard to see: Center the Moon, refocus, and use a lower magnification before increasing it gradually.
- The Moon is too low: Wait a few minutes for a clearer line of sight, but finish before the 9:11 P.M. moonset listed for 40° N, 90° W.
- You cannot identify Mare Fecunditatis: Start at the rounder Mare Crisium, then move downward in the telescope’s view to the darker Mare Fecunditatis.
- The ray is not obvious: Improve focus and observe when the Sun’s angle on the lunar surface produces stronger shadows and contrast; atmospheric haze can also wash out fine details.
- Your location differs from the reference: Check a local ephemeris or astronomy app for your Moon altitude, azimuth and moonset. The published times are not a worldwide timetable.
What to expect on October 15
This is a short, focused lunar observing target rather than an all-night event. The waxing crescent phase leaves much of the Moon in darkness while sunlight highlights the crater rims and the ejecta streak. Find the Moon promptly after twilight, identify the two maria, then spend the remaining time comparing the fraternal twins’ profiles. Their 4-mile (6-kilometer) separation and shared ray make the Messier–Messier A pair one of the clearest examples of a grazing lunar impact.
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