L60 Kies Pi (π)
A lone, gently rounded volcanic shield rising barely 150 meters above Mare Nubium, one of only a handful of genuinely solitary domes on the Moon — an unofficial Greek-letter name that has simply outlasted every attempt to replace it.
Source: IAU/Gazetteer & Sky & Telescope Lunar 100 (Wood, 2004)
L60 Kies Pi (π)
Mare Nubium · Volcanic Dome📉 Vital Statistics
🔭 Field Notes
Kies π sits by itself on the floor of Mare Nubium, sandwiched between the crater Bullialdus to the north and the long cleft of Rima Hesiodus to the south, just west-southwest of the low, lava-flooded remnant crater Kies. Unlike the crowded dome fields at Hortensius, the Marius Hills, or Mons Rümker, Kies π is a genuine loner — a single, gently rounded shield rising only a few hundred meters above the surrounding basalt, with slopes so shallow it all but vanishes under anything but very low, raking sunlight. Under the right terminator lighting a small summit pit becomes visible at its high point, the telltale sign of the vent that built it.
- ▶ An Oddity Among Domes: Most catalogued lunar domes occur in clusters or fields, but Kies π is one of a handful of genuinely solitary domes on the Moon, alongside similar loners like Milichius π and the Gruithuisen domes. That isolation, combined with its accessibility in modest telescopes, is a large part of why Charles Wood picked it to represent lunar dome volcanism on the Lunar 100 list.
- ▶ A Second, Very Different Neighbor: South of Kies π sits a much larger companion feature nicknamed “Kies 2” or the Kies megadome, with an elongated base roughly 51 by 34 km across, centered near 28.3°S, 23.8°W. Where Kies π is interpreted as a simple effusive shield built by lava erupting at the surface, researchers have proposed Kies 2 as an intrusive dome — a broad swelling raised by magma that never actually broke through, more akin to a terrestrial laccolith than a small volcano. The two features, so different in scale and likely origin, sit close enough to compare in a single wide-field view.
- ▶ Unofficial but Well Known: Despite being one of the most frequently sketched, imaged, and referenced individual domes in amateur and professional lunar literature alike, the Greek-letter designation “π” was never formally adopted by the IAU. It survives purely by longstanding observational convention, a naming quirk shared with several other solitary domes such as Milichius π.
📍 Nearby L100 Targets
- L54 Hippalus Rilles: A family of arcuate rilles roughly 200 km west, concentric to the Humorum basin and formed as the basin floor subsided under the weight of its own mare fill. Kies π’s effusive dome-building and the Hippalus rilles’ basin-scale subsidence are two very different ways the same broadly volcanic and tectonic history has left its mark on the mare floor.
- L81 Hesiodus A: The Moon’s best-known concentric crater, roughly 190 km southeast, its inner ring giving it a bullseye appearance unlike almost anything else on the Moon. It’s a useful contrast piece in the same session — a crater whose double-ring structure remains debated, next to a dome whose volcanic, effusive origin is comparatively well settled.
- L84 Pitatus: A large floor-fractured crater roughly 260 km southeast, on the southern shore of Mare Nubium, its floor threaded by the concentric Rimae Pitatus. Like Kies π, Pitatus shows signs of magma working on the crust from below — though here the result is a network of fractures rather than a dome.
🚀 Mission Log
Target Acquisition
Find Bullialdus, drop south to Kies, then hop west-southwest
Start at Bullialdus, a bright, sharply terraced 61 km crater sitting prominently on Mare Nubium — an easy landmark at almost any lighting. Move due south to Kies, a low, lava-flooded remnant crater whose rim survives only as scattered ridges, then look just west-southwest of it for a broad, gently rounded rise standing apart from the surrounding flat mare. That quiet swelling is Kies π — no rim, no bowl, just a low shield with a small pit at its summit.
Chase a very low terminator — this dome is barely 150 m tall
Kies π rises only about 150 m over a base roughly 10 km across, making it one of the subtlest profiles in the entire Lunar 100. Catch the terminator when it’s crossing this stretch of Mare Nubium, morning or evening, and the dome’s gentle slopes throw just enough shadow to reveal its rounded outline and the small summit pit at its high point. Under anything brighter than a very low Sun, the dome loses nearly all visible relief and becomes extremely difficult to distinguish from the surrounding basalt — there’s no in-between lighting that shows it half well.
Work up in power to find its much larger, flatter neighbor
At 100x–150x, once you’ve confirmed Kies π itself, look south for a second, much larger rise with an elongated base roughly 51 by 34 km across — nicknamed the Kies megadome. It’s far broader than Kies π but barely rises above the mare at all, and researchers have proposed it as an intrusive structure, a swelling raised by magma that never broke the surface, rather than a simple effusive shield like its smaller neighbor. Seeing both in the same low-Sun session illustrates how lunar volcanic uplifts may have formed through different processes.
Pair it with the rilles and craters ringing the same neighborhood
Roughly 215 km northwest, the Hippalus Rilles (L54) trace a concentric arc along the eastern shore of Mare Humorum, a useful contrast between tectonic flexure and Kies π’s quiet effusive volcanism. About 190 km southeast, Hesiodus A (L81) is the Moon’s best-known concentric crater, its double-ring structure still debated next to a dome whose origin is comparatively well settled. And roughly 260 km southeast, Pitatus (L84), with its own concentric floor rilles, shows magma working on a crust from below in yet another form.
📝 Observation Log — L60 Kies π
0/4 CompleteIs Kies π visible tonight?
Kies π sits on Mare Nubium near 26.5°S, 24.0°W, just west-southwest of the flooded crater Kies. Best viewing is around Waxing Gibbous (roughly Day 9), and unusually for this list, getting a very low sun angle matters more than the exact day: this dome rises barely 150 m above the mare and needs a near-grazing terminator to cast any shadow at all. Libration is not a meaningful factor at this longitude.
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When to Observe Kies π
Kies π is one of the subtlest profiles in the entire Lunar 100 — a lone shield rising barely 150 m above the mare, without the obvious rim-and-bowl profile of an impact crater to help it catch the light.
- For the Dome: You need a very low, grazing terminator. Kies π sits around 24°W on Mare Nubium, so its best light comes when the terminator is crossing that longitude. Track the terminator’s position rather than counting on a fixed day, since exact timing shifts a little with libration and solar colongitude. Under anything brighter than a very low Sun, the dome loses nearly all visible relief.
- For Orientation: Anchor on Bullialdus, a bright, sharply terraced crater on Mare Nubium. Move south to Kies, a low, lava-flooded remnant crater, then look just west-southwest of it for the dome’s quiet, rounded rise.
- Aperture and Seeing: A patience target more than an aperture target. Moderate power confirms the dome’s outline; picking out the small summit pit at its high point rewards higher power and steady seeing.
What to Look For
Look for a single, gently sloped rise about 10 km across, with a small pit visible at its highest point under favorable lighting — the telltale sign of the vent that built it.
Most catalogued lunar domes occur in clusters or fields — Kies π is one of the Moon’s better-known isolated volcanic domes, alongside similar loners like Milichius π and the Gruithuisen domes.
Look south of Kies π for a second, much larger rise with an elongated base roughly 51 by 34 km across, nicknamed the Kies megadome. It’s far broader than Kies π but barely rises above the mare at all, and researchers have proposed it as an intrusive structure — a swelling raised by magma that never broke the surface — instead of a conventional effusive volcanic dome like its smaller neighbor.
Revisit the same field later in the lunar day and watch the dome’s relief fade almost entirely into the surrounding basalt — a useful demonstration of just how lighting-dependent this whole category of feature really is.
The Science: Two Domes, Two Possible Origins
Sitting only tens of kilometers apart, Kies π and its larger neighbor may represent two different volcanic processes shaping the surface without either one ever forming a proper volcano.
A Simple Effusive Shield
Kies π itself is generally interpreted as a straightforward effusive dome, built by fluid lava erupting from a central vent and spreading outward in thin, gently sloped layers before cooling — a classic example of an effusive lunar shield dome, at a smaller scale than similar shield volcanoes elsewhere in the Solar System. Unlike the silica-rich Gruithuisen domes, Kies π appears to have formed from relatively fluid mare basalt, making it a textbook example of a typical lunar shield dome rather than one of the Moon’s rarer, more viscous “red spot” domes.
A Possible Intrusive Swelling to the South
The much larger Kies 2 megadome, roughly 51 by 34 km at its base, has been proposed as an intrusive dome rather than an effusive one — a broad uplift raised by magma pooling beneath the surface without ever erupting, more akin to a terrestrial laccolith than a small volcano. Its far lower relief relative to its size is one of the principal observations supporting this interpretation.
What Hasn’t Been Resolved
Morphometric and spectrophotometric studies have compared Kies π against its larger neighbor to support the idea that the two domes may have formed through different volcanic processes, but confirming an intrusive origin for a feature you can’t directly sample remains inherently difficult. Exactly how common this kind of paired effusive-and-intrusive dome system is elsewhere on the Moon is still an open question.
Most Lunar 100 domes reward you with a single, well-understood story. Kies π offers two — a small, well-behaved shield sitting only a short hop from a much larger, stranger swelling whose insides may never have reached daylight at all.