Hollow Moon Planetology: Blue Moon - Lunar Geography
by Sharon Dornhoff ((Everyone found a moon-map by
now...? If not, go get one -- otherwise, most of this won't make
any sense! Any map of Luna's visible surface that includes the
major craters' names will do; just remember that the Hollow Moon is
a mirror image of what you're looking at.))
Compass directions: mapping the Hollow Moon
Directions in the Hollow Moon setting can be tricky. North, South,
East and West can all be used; but they don't always match up, when
using different IRL moon-maps. Older maps of Luna often put South
on the top, and the definition of "east/west" can vary depending on
whether the mappers are taking an "Earth's-eye" perspective, or a
"Moon's-eye" one. In addition, there are two other directions --
"nearward" and "farward" -- which visitors to the Hollow Moon had
better get used to: Native Materans use them all the time.
The North and South Poles of Matera mark the two ends of the axis
upon which the moon rotates; the midpoint between them is the lunar
equator. Because the moon's axis of rotation is not as tilted as
Mystara's (less than 2 degrees, as opposed to 23), the Materan
equator always receives its sunlight head-on. The Northern and
Southern Hemispheres of Matera -- like those of Mystara or Earth --
encompass everything from their respective poles to the equator;
most of the Nearside's maria are in the Northern Hemisphere, while
Mare Orientale is in the Southern Hemisphere. The "north" and
"south" directions are understood and used freely by the Hollow
Moon's inhabitants, and shouldn't cause a problem.
East and West are where things start getting confusing. To
space-explorers approaching from Mystara or observers using a
telescope, the half of the moon which looks like "West" is the side
which includes Oceanus Procellarum. (This is the biggest dark area
you see, when you look up at Luna IRL.) The other half, with
several smaller dark areas, is usually called "East" by Mystaran
astronomers. That's how the PCs' maps of the outer Matera that they
bring from home will probably be labelled, and how most IRL
moon-maps label their compass-points as well.
Unfortunately, once PCs have actually arrived in the Hollow Moon,
they'll encounter a big problem with this perspective: it's over
the Oceanus Procellarum, where the lunar "dawn" occurs! The
brightening of the Firmament after fulldark, and the actual
appearance of the sun later in the month, take place in what a
Mystaran map calls the "west"... the exact reverse of the customary
situation for a planet*; and a reversal that's likely to get the
first PC who becomes lost in the Hollow Moon moving in the wrong
direction! Likewise, the lunar "dusk" actually transpires on what a
Mystaran map would call the eastern edge of the Nearside, as the
sun sinks beneath Mare Foecunditatis -- backwards, again.
[* - In the Hollow World, of course, there's no sunrise OR sunset,
only noon; so that setting's reversed east/west directions can't
become an issue, the way they can in the HM setting.]
Among native Materans, the corresponding two directions are
"dawnward" and "duskward": the former means the astronomer's
"west", and the latter, the astronomer's "east". Unfortunately,
attempts to translate these terms into Common are likely to give
the opposite answers, due to translators' preconceptions about
where the sun rises and sets! This could confuse the heck out of
explorers -- all the more so, if they don't realise the Hollow Moon
has a recognisable dawn or dusk, at all. (For purposes of these
posts, I'll be using "west" to refer to the direction of the lunar
sunrise and "east" for that of the lunar sunset, in accordance with
the moon-maps DMs are likely to be using.) The terms "Eastern
Hemisphere" and "Western Hemisphere" aren't used in the Hollow
Moon.
Along with north, south, dawnward, and duskward, natives of Matera
also have words to describe orientation relative to the
centre-point of the Nearside. "Nearward" and "farward" respectively
indicate a direction toward, and away from, the lunar point which
comes closest to the planet Mystara. (While Materans don't actually
know that Mystara is OUT there, they know that their whole world is
roughly-spherical, and that the habitable half of it -- the part
that's not Firmament -- has a midpoint.) On moon-maps IRL, lunar
coordinates (0,0) mark the exact centre of the Nearside; this can
also be thought of as a "pole" for an imaginary "Nearward
Hemisphere". Motion toward this geographic centre-point is
"nearward" motion. Conversely, lunar coordinates (180,0) mark the
centre point of the Farside -- i.e. the "pole" of a hypothetical
"Farward Hemisphere" -- and moving toward this distant point (and
away from (0,0)) constitutes "farward" movement. On a flat,
circular map of just the Nearside, "nearward" means toward the
middle, and "farward" means toward the edges; on a similar map of
the Farside/Firmament, the reverse is true.
Lands along the edges of the Nearside are called the "rimlands",
while those in the near vicinity of coordinates (0,0) are called
the "midlands". (If I've lost you, try thinking of Matera's
habitable hemisphere as a bowl that's balanced on the end of a long
pole: the pole represents a line from Mystara to Matera; the bowl's
rim is the rimlands; and the place the bowl touches the pole is
geographic point (0,0), at the centre of the midlands.) The special
terms "rimward" and "midward" are used only on those peninsulas of
habitable land that jut out beyond the Nearside/Farside border
(located at coordinates 90 E & 90 W longitude) -- compared to
which all the other Materan realms are "nearward" -- to better
distinguish moving toward regions on the fringe of the Nearside
from moving all the way to the midlands.
Matera, like Luna, has no magnetic field. Non-magical compasses
won't work there, although magic ones will. Native mages of Matera
have direction-finding spells that distinguish both the north/south
directions, and the nearward/farward ones.
Geographic overview: how the inner and outer moons correspond
Apart from being mirror-images, the geography of the Hollow Moon
and of the outer Matera are identical in their layout, sharing
virtually all of the same maria, highlands, and geology. Not only
are the open stretches of crystal which can be seen from space also
exposed within the satellite's interior -- albeit sometimes covered
by seawater, freshwater, and/or ice -- but the interior landscape
of the lunar highlands also corresponds to that of the outside ...
so much so, that a good crater-map of Luna can be the perfect guide
to the mountains and island chains within Matera! (In fact, I'll be
using the Earth-names of craters as landmarks, from here on in.
Native Materans have their own names for them, and Mystaran
astronomers surely do as well; but I'm not going to start re-naming
geographic features until we've worked out a cultural motif for
each of the major lunar societies. :-D)
Of the several outer-moon "seas", ten of them -- Maria Crisium,
Foecunditatis, Frigoris, Humorum, Imbrium, Nectaris, Nubium,
Serenitatis, Tranquillitatis, and Vaporum -- plus Oceanus
Procellarum, are also represented by exposed crystal in the Hollow
Moon. Some of the "bays", "lakes", and "marshes" which adjoin these
"seas" -- Sini Aestuum, Iridum, Medii and Roris; Lacus Somniorum;
Pali Somni and Putredinis -- may also be represented in the inner
world, depending upon their proximity to other regions of exposed
crystal, the adjacent terrain, and whether their IRL names inspire
the imagination (What DM could pass up the chance to take a name
like "Marsh of Putrescence" literally...? ;-D).
Of the moon's ten crystalline-bottomed interior maria, four --
Foecunditatis, Tranquillitatis, Crisium and Humorum -- are
saltwater seas; Foecunditatis and Tranquillitatis are connected to
one another by a narrow strait, while Crisium and Humorum are
bounded by land and have no direct connection to other maria.
Another body of water -- known to various native cultures as the
"Midland Ocean", "Vesper Ocean", or "Great Spindrift Sea" --
encompasses the Mare Vaporum, Sinus Aestuum, and Sinus Medii ...
plus ALL parts of Maria Imbrium, Nubium, and Serenitatis or the
Oceanus Procellarum which lie within 25 degrees of the Nearside's
midpoint at lunar coordinates (0,0)*. Another 30 miles of ice-flats
surround this Midland Ocean wherever it peters out on open crystal,
as these regions are periodically flooded by the Hollow Moon's
tides, then freeze solid between inundations. The remainder of
Maria Imbrium, Nubium and Serenitatis, like the better part of
Oceanus Procellarum, are exposed, frigid, desolate crystalbarrens.
Mare Nectaris -- true to its name -- is a freshwater lake: the only
body of fresh water in the Hollow Moon to sport a crystalline
bottom. Mare Frigoris, and the adjacent Sinus Roris, are
permanently ice-sheathed.
[* - Don't bother worrying about how many miles this is; just get
out the ol' compass and draw a big circle on the "maria" portions
of your moon-map, using 25 N & S latitude and 25 E & W
longitude as guides.]
The Hollow Moon is EXTREMELY active geologically, with more live
volcanoes per square mile than can be found in any part of Mystara,
barring uninhabitable deathtraps like Sind's Burning Waste. In
fact, vulcanism is responsible for every mountain, sinkhole, island
or caldera within the HM setting! Unlike the volcanoes on most
worlds, those within Matera aren't a product of plate tectonics or
vortices to the Plane of Fire; rather, the many "hot spots" which
generated the inner moon's rugged terrain are a direct product of
asteroidal or cometary impacts on the satellite's exterior.
Billions of years ago, during the Hollow Moon's geological
development, such impacts transferred sufficient energy into the
crystalline bedrock of Matera to superheat rock-layers beyond the
heat-resistant crystal, producing interior volcanic cones of all
sizes. Once a "hot spot" is generated in the interior of Matera, it
rarely cools down entirely; tidal influences from the
fast-orbiting, super-dense Patera exert sufficient gravitational
stress to keep the Hollow Moon's depths molten and active, even
millions of years after the most recent impact (the one that
created Mare Orientale) struck the visible moon.
Over time, many of the older or broader volcanic cones --
Deslandres, Ptolemaeus, Fracastorius, Hipparchus, Clavius, Janssen
and others* -- have collapsed, forming calderas, lakes, badlands,
or plains of rich volcanic soil. Other inland peaks*, such as
Arzachel, Langrenus, Aristoteles or the mighty Mt. Copernicus, grew
to fantastic heights in the low-pressure airlessness that prevailed
within Matera, before the Immortal Ka and his associates thickened
and oxygenated its atmosphere. Actual "ranges" of crater-born peaks
are all but unknown, in the Hollow Moon, as the basalt-heating
impacts which created them tended to occur at widely-separated
points in geologic history; the chief exception is the sprawling
Stofler-Walter-Purbach-Arzachel Range that overlooks Mare Nubium.
This long stretch of rugged semi-active peaks resembles parts of
the U.S. Pacific Northwest, and its mountains date back to a series
of impacts by a single asteroid that split into pieces just before
collision, tracing a line of "hot spots" not unlike the comet that
struck Jupiter a few years ago IRL. Other so-called mountain
"ranges", such as the Taurus and Caucasus, are actually lone
calderas which fragmented into many smaller cones, that later grew
independently. They don't form straight lines of peaks, the way
mountains tend to be arranged on planets with normal tectonic
activity.
[* - Get out those moon-maps; all these are IRL craters you should
be able to find on them! All craters on the outer Matera or Luna
correspond to either mountains, or collapsed calderas, in the
Hollow Moon. Pretty handy, huh? :-)]
While mountains in the "inland" parts of the moon are numerous and
densely-packed, volcanoes in the maria are few and far-between.
Impacts that hit bare crystal, on the outer moon, didn't have any
solid basalt to heat up, on the other side of the Materan bedrock.
However, some of them did transfer sufficient residual heat to the
moon's arid interior, to fuse encrustations of dust upon the inner
surface, creating "islands" of metamorphic rock within the
crystalline desolation of various lunar maria. Some of these
islands, such as the Fra Mauro or Haemus Isles, are large enough to
sustain their own vulcanism, and habitable to all manner of life
because of geothermal heat. Others, like the Carpathian or
Riphaeus-Ural Archipelagos, are too flat and ground-hugging to
retain active magma beneath their surface, offering "oases" of
inhabitable land in the midst of the crystalbarrens only for races
which -- like the cryions -- are capable of living comfortably in a
sub-zero environment. Encrustation-flats in Mare Vaporum and Sinus
Medii have long since been inundated by seawater ... and the
maeshimer of the Great Spindrift Sea have worked many architectural
wonders, with these stretches of fused-dust seabed.
Not all of the terrain within the Hollow Moon is a product of
individual asteroid-strikes on Mystara' satellite. By far the
oldest features on the Nearside, apart from the maria themselves,
are a handful of bluffs and ancient mountain ranges that originated
with the marias' creation (more about this later). The loftiest of
these are the Apennines, which mark the southeastern corner of Mare
Imbrium. Originally several times higher than Mt. Copernicus,
they're still the steepest of the Hollow Moon's few
mountain-clusters, despite the fact they've been shedding magma
into Mare Vaporum for the last billion-odd years. The Alps and Jura
Mountains, also surrounding Mare Imbrium, are much less impressive,
although equally ancient; the Juras were volcanically "dead" for
most of Matera's existence, but have been "revived" by nearby
cometary impacts in the relatively-recent geological past. Running
roughly parallel to the shoreline of Mare Nectaris, the Altai Scarp
rises up in an immense plateau; its cave-pocked surface was eroded
by windblown moon-dust, long before the Hollow Moon was made
habitable.
The last catastrophic event to shape the Hollow Moon was the impact
which created Mare Orientale, raised the Rook and Cordillera
Mountains, and opened the interior of Matera to a wider universe
for the first time. This same impact also produced visible
fracture-patterns thousands of miles long, within the crystalline
structure of the Firmament; split open a three-thousand-foot
fissure, Venturer Deep, in the silted seabed of Mare Humorum; and
gouged out a eighty-five mile crevice, the Alpine Valley, when the
ricocheting core of the comet that'd penetrated Matera finally came
to ground in the northern mountains. More recently (geologically
speaking), the introduction of water and a breathable atmosphere by
the Hollow Moon's Immortal protectors have generated such surface
features as "the Rilles" -- an Everglades-like region of marshes
and hummocks -- on Mare Vaporum's coastline, or the island-dotted
Lake Clavius in the south. All but a few regions of desolate land,
such as the arid wastelands of Sohktar or the arctic Shadow Zone
near the South Pole, have since become fertile, vegetated, and
populated by animals and lost races.
So what's this mean for my PCs...?
From an adventurer's point of view, the fact that vulcanism is
responsible for virtually all the Hollow Moon's landscape may not
seem very important. However, one consequence of this geologic
history is very relevant to a would-be spelunker: There are NO
limestone caves, of the sort adventurers are accustomed to
exploring, in the Hollow Moon! (In fact there's no limestone,
period; there hasn't been water in Matera long enough for such
sedimentary calcite to form.) Likewise, there's no familiar
stalactites and stalagmites; gargantuan Underdark-style caverns, of
the sort common to Graakhalia, the Broken Lands, and shadow elf
territory; or -- since the basalt's far too tough for mere running
water to erode through -- navigable subterranean rivers. Instead,
cave-delvers should be prepared for meandering lava tubes, zigzag
fissures along volcanic fault lines, and toxic or explosive
gas-pockets. Many underground areas have magma very close to them
and are sweltering-hot; others contain pools of boiling mud or
geysers that can spray the unwary, or fill up periodically with
steam from superheated springs. The few natural caves in Matera
which aren't volcanic in origin are the products of erosion by wind
or wave action ... like the Altai Scarp's shallow,
phanatrel-populated overhangs; or the smooth-walled sandstone
caverns along the southern coast of Mare Crisium.