L68 Flamsteed P
A once-substantial crater ring almost entirely drowned beneath the lava of Oceanus Procellarum — its buried northeast rim hiding the exact spot where Surveyor 1 made America’s first soft landing on another world.
L68 Flamsteed P
Oceanus Procellarum · Surveyor 1 Landing Site📉 Vital Statistics
🔭 Field Notes
Flamsteed P is barely a crater at all anymore — a once-substantial ring, roughly 112 km across, almost completely buried beneath the mare basalts that formed Oceanus Procellarum. All that survives above the mare surface is a broken circle of low ridges and hills, with the small, sharp-rimmed crater Flamsteed itself perched on the buried ring’s southern edge. Most planetary scientists read it as an ordinary ancient impact crater flooded from below, but a minority view holds that some or all of the ring-like terrain could be volcanic in origin rather than a simple drowned impact scar — a question the site’s most famous visitor never quite settled.
- ▶ America’s First Soft Landing: Surveyor 1 launched on May 30, 1966, and after a direct 63.5-hour coast to the Moon, its retrorockets cut off about 3.4 meters above the surface, letting the spacecraft fall freely onto flat ground within the northeast portion of the buried ring. It touched down on June 2, 1966, becoming the first American spacecraft to soft-land on another world, on just its first attempt after mission planners considered the chances of complete success to be modest, with some contemporary estimates placing them around 10–15%.
- ▶ A Precisely Chosen Flat Spot: The site was picked as a stand-in for future Apollo terrain, and the spacecraft came to rest within about 15 km of its intended target, on level ground roughly one crater-radius from the edge of a small, rimless 200-meter crater — exactly the kind of mare surface NASA needed to characterize before risking a crewed landing.
- ▶ A Ring Rediscovered by Its Own Shadow: The lander sat unremarked for decades until the Lunar Reconnaissance Orbiter imaged the site under low Sun angles in 2009, revealing both the spacecraft and its shadow and pinning down its exact resting place within the ghostly, half-buried ring it had helped make famous.
📍 Nearby L100 Targets
- L13 Gassendi: A 110 km floor-fractured walled plain on the northern shore of Mare Humorum, roughly 460 km south, its rille-cracked floor and volcanically intruded central peak forming the famous “diamond ring” with the fresh crater Gassendi A — one volcanic contrast to Flamsteed P’s own long-running, unresolved one.
- L44 Mersenius: A crater on Mare Humorum’s southwest shore, roughly 580 km south-southwest, whose floor bulges upward in one broad, unbroken dome rather than cracking apart — a quieter, still-debated case of sub-surface magma reshaping a crater from below, echoing the same open question posed at Flamsteed P.
- L42 Marius Hills: The Moon’s densest concentration of volcanic domes, cones, and sinuous rilles, spread across a plateau roughly 500 km north-northwest — unambiguous, small-scale basaltic volcanism in its most concentrated near-side form, offering a clear answer where Flamsteed P’s own volcanic identity remains genuinely uncertain.
🚀 Mission Log
Target Acquisition
Find Flamsteed first, then look for the ring around it
Locate Flamsteed, a small, sharp-rimmed crater in southwestern Oceanus Procellarum — an easy landmark in an otherwise open stretch of mare. Flamsteed sits perched on the southern edge of a much larger, mostly buried ring roughly 112 km across: what’s left of an old crater almost entirely drowned beneath the same lava that formed the surrounding mare.
Chase a low terminator to bring out the buried ring
What survives of Flamsteed P above the mare is just a broken circle of low ridges and hills, so grazing light matters here. Best viewing falls around Day 11 waxing or roughly Day 26 waning, when a low Sun angle throws enough shadow across the subtle ridge line to trace the ring’s outline. Under higher Sun, the ring all but disappears into the surrounding mare.
Work at low power first, then zoom in on Flamsteed itself
Because the ring spans over 100 km, start at 75x–100x to take in its full broken outline before increasing magnification on Flamsteed’s own sharp little rim. The Surveyor 1 spacecraft itself sits within the ring’s buried northeast portion, but it’s far too small to resolve in any amateur telescope — that discovery took the Lunar Reconnaissance Orbiter’s own high-resolution imaging. What you can do is identify the general area it touched down in, on the flat mare inside the ring’s northeast edge.
From Flamsteed P’s buried ring to Gassendi, Mersenius, and the Marius Hills
Roughly 460 km south, Gassendi (L13) is a floor-fractured walled plain whose rille-cracked floor and volcanically intruded central peak form the famous “diamond ring” with the fresh crater Gassendi A — one volcanic contrast to the long-running debate over whether volcanism also contributed to the modification of Flamsteed P. About 580 km south-southwest, Mersenius (L44) has a floor that bulges upward in one broad, unbroken dome rather than cracking apart — a quieter, still-debated case of sub-surface magma reshaping a crater from below. And roughly 500 km north-northwest, the Marius Hills (L42) offer the Moon’s densest concentration of volcanic domes and rilles — unambiguous, small-scale basaltic volcanism, in contrast to Flamsteed P’s own genuinely uncertain origin.
📝 Observation Log — L68 Flamsteed P
0/3 CompleteIs Flamsteed P visible tonight?
Flamsteed P sits in southwestern Oceanus Procellarum near 3.0°S, 44.0°W, around the small crater Flamsteed. Best viewing is around Waxing Gibbous (roughly Day 11) or Day 26 waning, since this buried, 112 km crater ring survives only as a broken circle of low ridges that needs a grazing terminator to trace. Libration is not a meaningful factor at this longitude.
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When to Observe Flamsteed P
Flamsteed P is preserved today only as a very subdued ring — what survives above the mare is just a broken circle of low ridges, so grazing light matters here as much as it does for any relief feature on this list.
- Chase a Low Terminator: Best viewing falls around Day 10-11 waxing or the equivalent waning phase, when a low Sun angle throws enough shadow across the subtle ridge line to trace the ring’s outline. Under higher Sun, the ring all but disappears into the surrounding mare.
- Start Wide, Then Zoom In: Because the ring spans over 100 km, start at 75x–100x to take in its full broken outline before increasing magnification on Flamsteed’s own sharp little rim.
- For Orientation: Locate Flamsteed, a small, sharp-rimmed crater in southwestern Oceanus Procellarum — an easy landmark in an otherwise open stretch of mare — perched on the southern edge of the much larger buried ring.
What to Look For
Look for a roughly 112 km ring of low, discontinuous ridges and hills, almost entirely buried beneath the mare basalts that formed Oceanus Procellarum — all that’s left above the surface of a once-substantial crater. It’s one of the classic examples used to illustrate a ghost crater: a demonstration of how mare volcanism can nearly erase a large crater without completely obliterating it.
Most planetary scientists interpret the ring as an ordinary ancient impact crater buried by later mare basalt flows, although some researchers have suggested that tectonic or volcanic processes may have modified or contributed to parts of the observed ring structure.
Surveyor 1 came to rest on flat mare ground within the ring’s buried northeast portion. The lander itself is far too small to resolve in any amateur telescope, but you can identify the general area it touched down in.
The site was picked as a stand-in for future Apollo terrain, and the spacecraft came to rest within about 15 km of its intended target — exactly the kind of mare surface NASA needed to characterize before risking a crewed landing.
The Science: A Buried Ring and a Historic Touchdown
Flamsteed P’s interest lies in two very different stories layered on top of each other — a nearly vanished ring whose precise geologic origin remains debated, and the modern engineering milestone that happened to land inside it.
Vital Statistics
Located at 3.0°S, 44.0°W, on Rükl chart 40, the buried ring spans about 112 km. It’s named as a satellite designation of Flamsteed crater, honoring the English Astronomer Royal John Flamsteed. Its L100 distinction: the Surveyor 1 landing site, paired with long-standing questions about the ring’s geologic origin.
America’s First Soft Landing
Surveyor 1 launched on May 30, 1966, and after a direct 63.5-hour coast to the Moon, its retrorockets cut off about 3.4 meters above the surface, letting the spacecraft fall freely onto flat ground within the ring’s northeast portion. It touched down on June 2, 1966, becoming the first American spacecraft to soft-land on another world, on its first attempt, at a time when mission planners considered the chances of complete success to be modest.
Mission Record
Surveyor 1 made the first American soft landing on the Moon here in June 1966, returning over 11,000 television images and providing engineering data that helped prepare for Apollo. The Surveyor program’s 1966 site survey selected the southwest Oceanus Procellarum area largely because it offered a smooth mare surface representative of candidate Apollo landing sites. In 2009, the Lunar Reconnaissance Orbiter imaged the site at low Sun angles, with Surveyor 1’s own shadow revealing its precise location within the ring more than four decades after touchdown.
Most Lunar 100 targets ask you to consider one story at a time. Flamsteed P asks you to hold two together — a nearly vanished impact ring of debated origin, and the exact patch of mare where a machine first proved America could land softly on another world.