The Planet Cain

Approximately Earth-sized;
just over one astronomical unit from its G-nine star;
15 % denser atmosphere;
more greenhouse effect;
20 hour day;
no moons;
32 degree axial tilt;
therefore, complicated seasons.

Is "no moons" possible? I have heard of several ways in which Earth's comparatively large Moon might have made our planet habitable, e.g., here, but I am not a scientist.

Dathyna

A peak of radiation from the planet Dathyna's massive, metal-rich, irregularly variable sun, which probably condensed near a recent supernova, destroyed civilization but produced a killer mutation which exterminated the parent race, appropriated its technology and now threatens the Polesotechnic League.
-copied from here. 

Sun middle-F type, 5.4 times as luminous as Sol, more white than gold;
less hydrosphere than Earth because solar ultraviolet splits water molecules;
lower mountains and continents;
shallow, tideless, algae-covered ocean over half the flatter surface;
slight axial tilt;
small edge effects;
poles similar to the equator;
steep air pressure gradient;
uplands of ice and rock;
large deserts with dust storms over red rock;
fertile areas with forests, meadows and crops;
the dominant species inhabiting large, partly ruined buildings. 

The Lunar Surface In Science Fiction

We are used to reading descriptions of the lunar surface in science fiction:

Verne's characters look down on it;
Wells' land on it;
Heinlein's live there.

However, from his suite in the Hotel Universe, Poul Anderson's Nicholas van Rijn sees an altered landscape. Forcefields hold air, an ozone layer, soaring trees and fountains, great blossoms and lamps on vine-like posts although beyond them are a crater floor, a ringwall, jewel-like stars, the silver Milky Way and the blue and white Earth, all making van Rijn's opulent suite look tawdry.

David Falkayn visits Elfland in Lunograd, a park with grass, arbors, flowers, tall trees and fountains, towers, colonnades, birds, elevated streets, small suns on bronze vines and an Avenue of the Sphinxes although again beyond them are a crater floor, a ringwall, stars in a black sky and Earth with the lights of megalopolises visible on its night side. Although technology makes the Moon inhabitable and even comfortable, the stellar universe remains beyond the works of men.

Going one stage further, Poul Anderson also wrote a short story about a project to terraform the Moon.

On The Moon In The Technic History

In 2057
There is an "Apollo University Communications" in Leyburg on Luna.

In The Twenty Fifth Century
Elfland, Lunograd, is "...a giant bubble of air..." (David Falkayn: Star Trader, p. 333) enclosed in an electromagnetic screen on the Lunar surface.

In Lunograd:

many corridors, including Gagarin, end at Titov Circus, an excavated cylinder with a domed skylight, showing Earth and stars, and thronged encircling balconies where Ivarsen Gems, the Martian Chop House and Serendipity Inc. do business;

a large sports goods store sells vac suits and vehicles and also collapsible boats with gaudy sails for low-weight sailing on the small Lake Leshy;

people float down dropshafts on gee-beams;

on many sublevels, wide, high, grime- and oil-overlaid corridors are crowded with freightways, robotic machines and pedestrians in work coveralls;

there are factories, warehouses, shipping depots and offices and odors of humanity, chemicals and electrical discharges;

hot gusts come from fenced grilles;

the constant vibration of the great engines is deep and almost subliminal;

the Hotel Universe will pay one million Commonwealth credits to any oxygen-breather whom it cannot accommodate and has twice spent more than a million, once to synthesize dietary requirements and once "...to fetch a symbiotic organism from the visitor's home planet." (p. 360)

Selenopolis is in Copernicus.

The capital of the Lunar Federation is, like Lunograd, in Plato.

In The Thirty First Or Thirty Second Century (see here)
Dominic Flandry must spend two weeks in Luna Prime after returning from a mission.

On Satan

We usually read about the deeds of conscious beings but there are dramatic events even in inanimate environments. The rogue planet, Satan, has fallen to just over one astronomical unit from the blue giant, Beta Crucis:

this newly acquired sun, with four times the angular diameter of Sol, "...rage[s] on the horizon..." (David Falkayn: Star Trader, p. 449);

the sky is incandescent;

the roiling clouds are white with steam, black with volcanic smoke or gray but lightning-lit;

terrible winds, rain, Satan-quakes and floods lash stony plains;

glacial melt cascades from mountain flanks;

vapor spreads over half a continent, becoming mist in the chill air, but is cut by a tornado, then dispersed by gales;

island-sized icebergs, concealed by monstrous waves, collide and are destroyed;

the turbulent upper atmosphere rocks the descending spaceship - clamor and thunderstorms;

Falkayn, naming the planet, is interrupted by "...blindness and racket..." (p. 450);

tropical afternoons have clear skies followed by violent weather with wind velocities over 500 kph and rising;

the antarctic has heavy rain and frequent supersqualls;

a strong front from the cold north preserves comparative atmospheric tranquility;

Muddlin' Through lands near the arctic circle on an unflooded stable northern continent shortly before dawn;

Falkayn sees dark rock, mountain crags, white glaciers, clear stars, streaking meteors and dancing aurora;

the atmosphere is unbreathable and minus 75 degrees Celsius;

the ground is below minus 200 and will take years to warm;

conditions will always vary, causing chaotic weather;

leaving the ship, Falkayn stands not on a new world but on an old world reborn;

cold and stellar radiation mean that he can spend only half an hour outside;

when he has collected data and samples and started back, a cliff explodes and a torrent of liquids and solids engulfs him.

Suleiman II

I am reading about the planet Suleiman but finding that I have posted about it before. See here. However, I have also found some previously unnoticed details:

local gravity is 40% greater than Terrestrial although trading post staff are protected inside their compound's forcefield;

the air recycler in Dalmady's airsuit must cope with the hydrogen that seeps through everything (in "A Little Knowledge," the problem is helium seeping through everything);

the planetary core is overlaid by ice mixed with rock and  "...penetrated by tilted metal-poor strata." (The Van Rijn Method, p. 527);

because the planetary radius is 17,000 kilometers, Dalmady cannot discern the horizon of the ammonia sea through the red mist;

the city has an elaborate pattern but no streets;

the culture is fireless and neolithic;

most traffic is pedestrian;

animals, draught or ridden, are vaguely dinosaur-like;

Dalmady hears wind, waves, feet and wagons;

Suleimanites do not talk casually but do communicate continually by gesture, fur ripples and scents;

their year equals twelve and a half Terrestrial;

Suleimanites provide labor, saving the cost of automatic machinery, and are becoming dependent on metal, plastic and energy-cell trade goods.

The Endless Details Of The Technic History

Copied from Poul Anderson Appreciation, 17 September 2016:

Eridanus is a constellation. Thus, "Alpha Eridani I" would mean "the first planet of the first star in Eridanus." I do not know that there is such a planet but I understand that this would be the correct terminology. So what does "02 Eridani A II" mean? (See Poul Anderson,  David Falkayn: Star Trader, p. 224.) I have found a reference to 02 Eridani B but do not understand it. In any case, 02 Eridani A II is a planet named Ta-chih-chien-pih by its inhabitants and Cynthia by human beings.

Chee Lan from Cynthia remembers "...warm ruddy sunlight and rustling leaves around treetop homes..." (pp. 224-225) We see a Cynthian colony on another planet in The Game Of Empire. These details about Cynthia come immediately after the details about the Merseian city of Ardaig in "Day of Burning."

"Poul Anderson immerses you in the future....Anderson puts you into a whole new world."
-Larry Niven, quoted on the back cover of David Falkayn: Star Trader.

This is an accurate account of Anderson's achievement and I would add that Anderson immerses us more effectively even than Robert Heinlein did.

In And Around Castle Afon

Copied from Poul Anderson Appreciation, 17 September 2016:

A bannister carved like a snake;
spacious rooms;
reptile-skin carpets;
mounted animal skulls;
crimson-draped walls;
balcony view of garden and Ardaig;
garden reminiscent of Japanese;
gray stone buildings;
fantastic turrets and battlements;
estates on the hills;
high modern buildings on the bay;
cargo ships and a jet;
nonessential traffic banned in this sacred Old Quarter.

Falkayn finds the decor disquieting but is by now well accustomed to alienness. As I have mentioned before, he remains perfectly relaxed while conversing with bizarrely shaped beings.

In this post, I have summarized two paragraphs of "Day of Burning." I suspect that Poul Anderson imagined all these details from the carved snake bannister to the sacred Old Quarter while writing these paragraphs and that we as readers usually forget them as soon as we move on to the dialogue between Falkayn and his servant.

The Audience Chamber Of Castle Afon

Copied from Poul Anderson Appreciation, 17 September 2016:

Centuries apart, both David Falkayn and Max Abrams stand in the audience chamber of Castle Afon in Ardaig on Merseia. Falkayn is Nicholas van Rijn's protege and Abrams is Dominic Flandry's mentor.

Falkayn sees:

a high, gaunt, echoing chamber of unhuman proportions;
woven tapestries on stone walls;
windows arched at top and bottom;
battle banners hanging from rafters;
a hearth with a fire big enough to roast an elephant;
armored, demon-masked troopers lining the hall, bearing curved swords, barbed pikes and guns;
the Hand of the Vach Dathyr in orange robes and horned miter.

Abrams sees:

long, flagged floor;
high walls;
narrow windows arched at top and bottom;
sawtoothed vaulting;
proportions wrong by Terran criteria but not here;
demonic mask helmets on suits of armor;
faded tapestries;
rustling battle banners;
unhuman symbology;
a dragon carved in black wood;
the black-robed Hand of the Vach Ynvory lifting a spear and crashing it down in salute.

Some of us might remember James Blish's Jack Loftus in the audience room of the Hegemon of Malis (here).

Distance And Giganticism

Copied from Poul Anderson Appreciation, 1 September 2016:

In this post, we compare and contrast an adult fantasy novel with a juvenile sf novel:

Poul Anderson, Three Hearts And Three Lions (London, 1977);
James Blish, Mission To The Heart Stars (London, 1980).

(When referring to CS Lewis, we found an accidental "Lion" theme in the titles. With Blish, there is an accidental "Heart" theme.)

Distance
Anderson's Holger Carlsen has been transported from our Earth or one like it to a mythological Earth where a demon says that:

"'...ye are from far away, so far that a man might travel till Judgment Day and not reach your home.'" (Three Hearts..., Chapter Two, p. 22)

- and, after arriving in that distant world, Holger must make a long journey by horseback into Faerie.

Blish's Jack Loftus and his companions take well over two years at faster than light speeds to reach the galactic Heart Stars. Thus, Jack travels not only to the galactic center but also into adulthood: a rite of passage story.

Giganticism
Invited to dinner, Holger enters:

"...a chamber so huge he could scarcely see the end or the ceiling." (Three Hearts..., Chapter Seven, p. 45)

They dance in an even larger chamber.

The Heart Stars confederation is called the Hegemony of Malis. When Jack enters the Hegemon's audience room:

he compares it to the Hall of the Mountain King;
it is of stone and artificially lit;
its ceiling cannot be seen;
Jack feels that there might be clouds beneath the ceiling;
it is like the universe's biggest cathedral although not cathedral-like in atmosphere;
many unidentifiable machines, all dissimilar, are spaced along its walls;
the place is uncluttered, austere and built to last, away from earthquake zones;
the Hegemon is over eight feet tall, blocky, powerful, granite-colored, facially resembling an Easter Island statue and wearing an undecorated black tunic with bare arms and legs;
although Earth has made an alliance with the immortal Star Dwellers, who are capable of collapsing galaxies, the Hegemon's machines predict that the Dwellers will not intervene if the Hegemony forcibly annexes Earth;
he so orders.

In The Hall Of The Mountain-King, Whether On Earth Or On Merseia

Copied from Poul Anderson Appreciation, 28 June 2916:

The hall of troll-king Illrede:

in a mountain cave;
vast;
hewn out of rock;
stolen gems and tapestries on the walls;
expensive goblets and cloths on ebony and ivory tables;
fires burning down the length;
rich garments on troll lords and ladies;
elf, dwarf and goblin thralls carrying trenchers of human, Faerie and animal meat and cups of southern wine;
snarling music;
smoky air;
ruddy light;
guards, "...moveless as heathen idols...," (The Broken Sword, p. 64) with glinting spears;
gobbling, guzzling, quarrelling trolls;
a thunderous din;
quiet lords in carven seats;
Illrede, fat and wrinkled, with long green tendrils for a beard and wearing a gold crown.

Colorful, barbaric and vividly imagined. Since trolls are large, green, humanoid and hostile, comparisons with Poul Anderson's alien Merseians are inevitable. In the audience chamber of Castle Afon:

"The mask helmets on suits of armor grinned like demons. The pattern of faded tapestries and rustling battle banners held no human symbology. For this was Old Wilwidh, before the machine came to impose universal sameness. It was the well-spring of Merseia. You had to see a place like this if you would understand, in your bones, that Merseains would never be kin to you." (Young Flandry, p. 141)

Haven

Haven is the second moon of Cat's Eye, which is a gas giant of 1.3 Jovian masses and the fourth planet in the system of the G2 star, Byers. Radiation from Cat's Eye, not from Byers, makes Haven marginally habitable.

Haven:

is tidally locked but on the Mercurian, not the Lunar, model;

is smaller than Earth with a thinner atmosphere;

has -

great seismic activity because of its proximity to Cat's Eye,
high rocky mountains,
deep valleys,
one almost comfortable valley, Shangri-La, near the equator,
terrestroid biochemistries but dangerous native organisms,
been inhospitable to seeded Terrestrial organisms;

was created by Jerry Pournelle but Poul Anderson wrote one story set there.

Aeneas

Copied from Poul Anderson Appreciation, 6 Mar 2016:

The text of this post is copied from here.

..a complicated colonial society. Seven centuries earlier, scientists wanting to study the unusual natives of the planet Dido which is unsuitable for human habitation colonized another planet in the same system, Aeneas, where they established a University that attracts human and non-human students from other systems. Survival in the sparse Aenean environment required cultivation of large land areas with both native and imported plants and animals. Horses and green six-legged stathas were imported as transport animals. During the Troubles, “Landfolk” relationships became semi-feudal and the University incorporated military training into its curriculum. Near the main University campus is a statue of Brian McCormac who cast out nonhuman invaders.

Later immigrants seeking a refuge or a new start are excluded from the tri-cameral legislature by a property qualification for the franchise but form subcultures: tinerans, Riverfolk, Orcans and highlanders. Orcans guard ruins left by space-traveling “Ancients.” “Lucks,” small pets kept in Tinerans’ caravans, are telepathic parasites left by the Ancients. Most Townfolk, belonging to ancient guilds, identify with scientists and squires. However, industrialization in the urban area known as the Web has produced manufacturers, merchants and managers whose interests are closer to those of the Empire which forcibly annexed Aeneas after the Troubles and re-occupied it after Hugh McCormac’s rebellion. Chunderban Desai, High Commissioner of the Virgilian system, consults Thane of the University and Jowett of the Web about McCormac’s Landfolk nephew who will inherit tri-cameral Speakership but meanwhile attacks Imperial troops, then hides among tinerans before traveling with Riverfolk to meet the new Orcan prophet.

I summarize Aenean society in order to convey the richness of detail in Anderson’s fictitious planets.