L43 Wargentin
A crater filled to the brim with lava, its floor risen almost level with the rim to form a raised plateau rather than a bowl — sitting just southwest of Schickard, near enough to the limb that favorable libration makes a real difference.
L43 Wargentin
SW Limb · Lava-Filled Plateau Crater📉 Vital Statistics
🔭 Field Notes
Wargentin sits on the extreme southwestern limb, the odd member of a tight chain of formations that also includes Schickard, Nasmyth, and Phocylides. Because it’s so close to the limb, favorable libration only brings it fully into view roughly every other lunation. What makes it worth the wait is that Wargentin runs against the usual rule of crater anatomy — floors are supposed to sit below the surrounding terrain, and Wargentin’s doesn’t, making it one of the Moon’s clearest examples of a crater turned into a raised plateau. Instead of a bowl, the telescope shows a level, raised tabletop standing above the highlands around it, best appreciated at low sun angle when its rim casts long shadows onto — or rather above — the plain it should have sunk into.
- ▶ The Sealed Crater: After Wargentin’s impact basin formed, basaltic lava later flooded the interior and accumulated to an unusually high level, filling the bowl almost to the brim without ever overtopping the rim — leaving a nearly flat plateau standing proud of the surrounding terrain instead of the depression most craters have.
- ▶ Lava or Ejecta?: For years the fill’s unusually high albedo, brighter than typical basalt, left it unclear whether the plateau was solidified lava or a fluidized ejecta deposit related to the nearby Orientale basin, echoing a similar debate at Schiller. A well-known 2006 Lunar Photo of the Day piece framed this as the “lava or ejecta” question; the interpretation that’s generally favored now is a basaltic lava flow, with a later, thin dusting of ejecta across the surface helping account for its brightness.
- ▶ Wrinkle Ridges: A network of wrinkle ridges crosses the plateau surface, branching in a pattern some observers liken to a bird’s footprint. It’s most visible at a very low sun angle along the terminator.
📍 Nearby L100 Targets
- L30 Schiller: A strikingly elongated, roughly 180 km-long “footprint”-shaped crater around 420 km east-southeast. Its Lunar 100 listing favors an oblique impact as the likely cause of the elongation, though some sources describe it instead as a fusion of two or more overlapping craters. Its own smooth, lava-flooded floor makes a natural comparison with Wargentin’s flat-topped plateau just to the west.
- L39 Schickard: The huge walled plain immediately northeast, more than twice Wargentin’s diameter, with its own light-and-dark banded floor from a mix of Orientale ejecta and darker mare lava. Together the two form the standard example of how differently a lava-flooded crater floor can end up looking depending on how the flooding actually played out.
- L59 Schiller-Zucchius Basin: A largely buried, badly degraded 325 km Pre-Nectarian peak-ring basin roughly 310 km southeast, its eroded outer ring arcing past Schiller’s northeast margin. It carries one of the Moon’s confirmed mascons, and its ancient, worn-down profile is a useful counterpoint to Wargentin’s comparatively crisp, still-legible plateau.
🚀 Mission Log
Target Acquisition — L43 Wargentin
Anchor on Schickard, then drop southwest to the chain
Start at Schickard, the huge ~212 km walled plain near the southwestern limb — unmistakable even at low power thanks to its size and its banded, part-flooded floor. Wargentin sits just southwest of Schickard’s rim, the odd member of a tight chain that continues on through Nasmyth, connected to Wargentin’s southeast rim, and Phocylides, the larger crater overlaying Nasmyth beyond that. All four sit close enough together to fit in a single wide-field view, so once you’ve found Schickard, the rest of the chain is a short hop away.
Time it for a raking terminator, and be patient with libration
Wargentin’s whole appeal — a crater floor standing above the surrounding highlands instead of below them — only reads clearly under oblique light. Aim for occasions when the terminator lies near this stretch of the southwestern limb and shadows are running long across the region; exact timing shifts with libration and solar colongitude, so there’s no fixed day count to chase. Because Wargentin sits so close to the limb, favorable libration doesn’t line up every lunation — expect a session where it’s simply too foreshortened to work, and try again next month rather than assuming a poor night is the problem.
Work up in power to read the plateau’s surface
At 75x–100x, compare Wargentin’s flat, level top against Nasmyth’s ordinary bowl-shaped floor right next door — the contrast is the whole point of the target. Push to 150x+ near the terminator and look for the network of low wrinkle ridges crossing the plateau, branching in a pattern some observers liken to a bird’s footprint, plus the handful of small craters that overlie Wargentin’s worn rim. Use Nasmyth’s attachment point along Wargentin’s southeast rim as a fixed reference for orientation while you work.
Pair it with the neighbors it keeps unusual company with
Schickard (L39) sits immediately northeast and rewards the exact same terminator lighting, so it’s a natural first or last stop on the same session. Further out, the elongated “footprint”-shaped crater Schiller (L30), east-southeast along the same southwestern limb, and the badly degraded Schiller-Zucchius Basin (L59), southeast of Wargentin, both belong to the same neighborhood — worth a look on a night when libration is favorable enough to take in the whole region, since all three depend on that same low, raking light to show their relief.
📝 Observation Log — L43 Wargentin
0/4 CompleteIs Wargentin visible tonight?
Wargentin sits just southwest of Schickard, close enough to the limb (~60°W, 50°S) that the best viewing is concentrated around Waxing Gibbous (roughly Day 12–13), when grazing light reveals the raised, lava-filled plateau standing above the surrounding terrain instead of sinking into it like an ordinary crater. Near Full Moon, higher sun brings out the plateau’s albedo contrast instead of relief, offering a secondary way to spot it. Favorable libration toward the southwest isn’t strictly required, but it helps considerably here, both bringing the feature further onto the disk and countering the foreshortening from its high southern latitude.
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When to Observe Wargentin
Wargentin’s whole appeal is a trick of geometry: a crater floor that stands above the surrounding highlands instead of below them. That illusion only reads clearly under raking light, and this target has a second timing problem most L100 craters don’t — it sits close enough to the southwestern limb that you’re also at the mercy of libration.
- For the Plateau: You need the terminator running close to this stretch of the southwestern limb, with shadows falling long across the region. There’s no fixed day count to chase here — exact timing shifts with libration and solar colongitude from one lunation to the next, so it’s worth checking conditions session by session rather than counting days from a quarter phase.
- For Libration: Wargentin’s proximity to the limb means favorable libration doesn’t line up every month. Expect the occasional session where the whole chain is simply too foreshortened to work — that’s a libration problem, not a bad night.
- For Orientation: Anchor on Schickard first — the huge, unmistakable walled plain northeast of Wargentin — then drop southwest to pick up Wargentin, Nasmyth, and Phocylides as a single tight chain.
What to Look For
Crater floors are supposed to sit below the surrounding terrain — Wargentin’s doesn’t. At 75x–100x, compare its flat, level top directly against Nasmyth’s ordinary bowl-shaped floor right next door. Instead of a depression, you’re looking at a raised, tabletop plateau standing proud of the highlands around it.
After the impact basin formed, basaltic lava flooded the interior. The fill is interpreted as having accumulated almost to the rim crest without ever overtopping it — the mechanism behind the plateau: not an unusually shallow crater, but an ordinary one filled almost exactly to the top.
Push to 150x or higher near the terminator and look for a network of low wrinkle ridges crossing the plateau surface, branching in a pattern some observers liken to a bird’s footprint. They’re subtle enough that only raking light will bring them out.
Wargentin’s fill is unusually bright for basalt, and for years that left it genuinely unclear whether the plateau was solidified lava or a fluidized ejecta deposit related to the nearby Orientale basin. No eyepiece will settle that question for you, but knowing it’s there adds real weight to what you’re looking at.
The Science: A Crater Flooded Almost to Its Rim
Wargentin is a rare case where the anatomy itself is the mystery. Most flooded craters just have a smooth floor; this one has a floor that stretched expectations for what a flooded floor is supposed to look like.
Bright Enough to Question
The plateau’s unusually high albedo, brighter than typical basalt, was the whole reason the lava-or-ejecta question existed in the first place. A well-known 2006 Lunar Photo of the Day piece framed it in exactly those terms, and Clementine’s multispectral data later provided important compositional evidence in weighing the two explanations. The interpretation generally favored now is a basaltic lava flow with a later, thin dusting of ejecta helping account for the brightness — echoing a similar debate at nearby Schiller.
Ridges From Within
The wrinkle ridges crossing the plateau aren’t just cosmetic — they’re generally read as compressional tectonic features, formed as the basalt fill contracted and experienced compressional stress after emplacement, the same broad family of features that shows up on flood-basalt surfaces elsewhere on the Moon. LRO’s LOLA altimetry has since confirmed just how level the plateau surface really is relative to the highlands around it, and LROC imaging has resolved the ridge network — sometimes called Dorsa Wargentin — in detail.
What Hasn’t Been Resolved
The precise mechanics of a lava fill that rose almost exactly to rim height without ever overtopping it are still not pinned down in any detailed, quantitative way. Exactly why volcanic flooding ceased so close to rim level remains uncertain, and connecting that outcome cleanly to a specific eruption history remains an open question.
Most Lunar 100 crater targets reward you for what happened inside a bowl. Wargentin is the rare case where the bowl itself almost disappears — a crater flooded so completely it nearly stopped looking like a crater at all, and became a landform of its own.