L39 Schickard
A vast, ancient walled plain near the southwest limb, its low, worn rampart enclosing a floor draped in a pale stripe of ejecta — material blown in from the distant Orientale basin, mixed with darker basalt that later welled up from within.
L39 Schickard
Southwest Limb · Orientale-Sculpted Walled Plain📉 Vital Statistics
🔭 Field Notes
Schickard is a huge, ancient walled plain near the southwest limb, appearing distinctly oblong when viewed from Earth due to foreshortening near the edge of the disc. Its floor is nearly level but its coloring, as 19th-century observer T. W. Webb noted, is strongly varied — a triangular band of lighter highland material crosses the floor, flanked by darker patches of lava in the north and southeast, a striping effect most visible under a high Sun. Long after Schickard formed, the distant Mare Orientale impact — nearly 1,200 km away — left its mark here too, scattering bright ejecta across the floor and carving radial furrows and graben into the western wall, broadly radial to Orientale.
- ▶ The Striped Floor: A broad triangular band of light-toned material — generally interpreted as Orientale-related ejecta mixed with local highland deposits — crosses the floor, set against darker basaltic patches to the north and southeast, one of the most visually distinctive floors of any large lunar crater.
- ▶ Orientale’s Reach: The western wall carries linear furrows and graben broadly radial to Mare Orientale, physical evidence of just how far that basin-forming impact’s effects extended across the lunar surface.
- ▶ Attached Neighbors: The crater Lehmann is attached to Schickard’s northern rim, the smaller Drebbel sits to the northeast, and the irregular Schickard E breaks across the southeastern rim — a small crowd of satellite features around the main plain.
📍 Nearby L100 Targets
- L30 Schiller: A striking 179 × 71 km elongated “footprint” crater to the northeast, another southwestern-highlands feature whose distinctive shape, like Schickard’s floor banding, has been linked to the same era of intense basin-forming impacts.
- L43 Wargentin: An 84.69 km crater just southwest of Schickard, uniquely filled to the brim with dark basaltic lava, forming a flat-topped plateau rather than a normal crater floor — one of the most distinctive landforms on the Moon and a striking neighbor to Schickard’s own lava-striped interior.
- L97 Inghirami Valley: A wide, straight 145 km valley (Vallis Inghirami) further southwest, radial to Mare Orientale and ending at the northern edge of the crater Inghirami — another direct line pointing back to the same distant impact that sculpted Schickard’s western wall.
🚀 Mission Log
Target Acquisition — L39 Schickard
Anchor on Mare Humorum, then follow the highlands to the limb
Start at Mare Humorum, an easy naked-eye dark oval on the southwestern near side. Work south-southwest across the intervening highlands until you reach a huge, distinctly oblong rim right at the edge of the disc — that foreshortened shape is Schickard itself, one of the largest walled plains visible from Earth at 212 km across. Its size and limb-hugging position make it unmistakable once you know to look for the elongated outline rather than a true circle.
Plan two sessions — low Sun for the walls, high Sun for the floor
Schickard rewards different lighting for different features. Catch it near the terminator to see the worn, terraced rim and the wall’s structure in relief. Come back under a high Sun, when shadows have mostly vanished, and the floor’s real attraction appears instead: a broad, light-toned band crossing darker basaltic patches to the north and southeast — a striping effect that only shows up once shadow relief stops competing with it.
Work up in power to trace the stripe and the Orientale scars
At 75x–100x, follow the triangular light band across the floor and note how it sets off the darker lava patches to either side. Push to 150x+ and look along the western wall for subtle linear features and furrows, faint scarring broadly radial to the distant Orientale Basin. While you’re at higher power, pick out the attached satellites: Lehmann on the northern rim, smaller Drebbel to the northeast, and the irregular break of Schickard E across the southeastern rim.
Pair it with the wider Orientale-sculpted neighborhood
Wargentin (L43) sits just southwest, its lava-filled floor a striking counterpoint to Schickard’s own two-tone one — filled flat to the brim rather than banded. Further southwest, the straight, 145 km Vallis Inghirami (L97) points radially back toward Orientale, associated with the same impact whose ejecta and stresses left their mark on Schickard’s western wall. To the northeast, the elongated “footprint” crater Schiller (L30) rounds out the group — all four sit close enough to work in a single session once libration is favorable.
📝 Observation Log — L39 Schickard
0/4 CompleteIs Schickard visible tonight?
Schickard sits well out toward the southwest limb (~55°W, 44°S) — best around Waxing Gibbous (roughly Day 11–12), when the low sun angle throws the worn rim into relief and starts to bring out the floor’s light-and-dark banding. The opposite terminator crossing falls close to New Moon and is much weaker, though favorable libration can still help bring out some rim detail then. If you’d rather see the full extent of that pale Orientale ejecta stripe than just its shadowed edge, come back near Full Moon, when high sun brings out the albedo contrast instead of relief. Favorable libration toward the southwest generally improves the view of the floor.
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When to Observe Schickard
Schickard is a huge target — one of the largest walled plains visible from Earth — but its position out toward the southwest limb means it looks quite different depending on when you catch it. Timing your session to what you actually want to see, rim relief versus floor color, matters more here than for most Lunar 100 targets.
- For the Worn Rim: Best around Waxing Gibbous, roughly Day 11–12, when the terminator is nearby and low sun angle throws the degraded wall and interior ring-plains into relief. The opposite crossing falls close to New Moon and is much weaker.
- For the Floor’s Light-Dark Banding: Near Full Moon, when high sun brings out the albedo contrast between the pale central stripe and the darker basalt patches to its north and south — this detail is largely washed out under low, raking light.
- Libration: Favorable libration toward the southwest helps considerably, both opening up more of the floor’s interior ring-plains and easing the foreshortening this near-limb position causes.
What to Look For
Schickard’s true footprint is a roughly circular walled plain some 212 km across, but its position near the southwest limb compresses that circle into a visibly oblong shape from Earth. Note the smaller crater Lehmann attached to its northern rim, and Drebbel a little farther to the northeast — both useful reference points for orienting yourself before working inward.
Scan the floor south of center for three larger ring-plains, remnants of smaller impacts on Schickard’s vast interior. A further set of five smaller ring-plains sits near the inner foot of the west wall, but these only come into view under favorable libration. On the southeastern rim, look for the breach made by the irregular crater Schickard E, the most prominent of several smaller craters overlying the worn outer wall.
Near Full Moon, look for a broad, lighter-toned band running roughly north-south across Schickard’s floor, leaving darker patches in the north and southeast. This striping is Schickard’s signature feature: a mix of light highland material blown in from the distant Orientale basin and darker basalt that later welled up from beneath the floor in the north and south.
For a genuine advanced challenge, watch the northeastern part of Schickard’s still-dark floor when the morning terminator sits at roughly 54–55°W. Under just the right lighting, observers have reported three illuminated points appearing as a small, roughly equilateral triangle, briefly lit peaks catching the first sunlight before the surrounding floor. This kind of clair-obscur effect is fleeting and needs both the right longitude and careful timing to catch.
The Science: A Basin’s Reach, an Ancient Survivor
Schickard’s patchwork floor is where two very different chapters of lunar history overlap: the ancient crater itself, and a much later, distant impact whose debris happened to land squarely across it.
An Ejecta Blanket From Over a Thousand Kilometers Away
The pale stripe on Schickard’s floor is interpreted as material thrown out by the Orientale basin impact, whose center lies roughly 1,200 km away near the Moon’s western limb. That distance is a useful sense of scale for just how far a major basin-forming impact can scatter recognizable ejecta, still identifiable as a distinct light-toned deposit long after it settled onto older terrain.
A Pre-Nectarian Survivor, Only Partly Flooded
Schickard dates to the Pre-Nectarian period, among the oldest impact events preserved in the lunar record, consistent with its low, heavily worn rampart. Unlike a fully mare-flooded basin, lava only partially resurfaced its floor, leaving the southwestern portion rough-textured and uncovered. That partial flooding makes Schickard a useful in-between case for studying how basalt filled large basins unevenly rather than all at once.
What Hasn’t Been Resolved
The exact sequence of events, how much of the floor had already been flooded by the time Orientale’s ejecta arrived, and how the two materials came to mix as thoroughly as they appear to, is still debated. Similarly, why the five smaller ring-plains cluster specifically near the inner foot of the west wall, rather than being distributed more evenly across the floor, doesn’t have a settled explanation.
Schickard rewards patience with two very different faces: a relief-rich, terraced ruin near the terminator, and a broad canvas of mixed light and dark material near Full Moon, each telling a different part of the same very long story.