I suppose the audience for this is quite niche, but I'm going to go ahead and summarize a very early hard SF story namely Kepler's Somnium (Dream).
Background Johannes Kepler (1571 – 1630) was a German Renaissance astronomer, astrologer, and mathematician. 1/

He is wrote the Epitome astronomiae Copernicanae in which he formulated heliocentrism (based on Copernicus, but with elliptic trajectories). Now, heliocentrism was a total game changer because it opened the possbility to a plurality of worlds 2/

To get a sense of how radical and shocking, one reason heliocentrism faced such difficulty is that we would expect a parallax among the fixed stars. Since we don't that must mean the cosmos is truly enormous, and the stars very far away. Copernicus' reply: it is simply so. 3/

So folks had to swallow an enormous universe, which opened up (even before people conceived of galaxies and such) a plurality of worlds. Think of e.g., Giordano Bruno's De l'infinito universo et mondi, an infinite universe filled with worlds. 4/

So, the dream (Somnium) was written around 1611, and Kepler's aim was to show what astronomy would look like as seen from another planet. This is a kind of long thought experiment to play with the idea of non-geocentrism 5/

It starts out with a narrator who "attentively contemplated the Moon and the stars I peacefully settled on my couch and fell into a rather deep sleep. In my sleep I seemed to have picked up a book, from the bookshelf to read it through." - he reads the book ... 6/

Then we get introduced to Duracotus and his mother Fiolxhilde, they are both Icelanders. The mother is a witch, making herbal remedies for the captains of nearby ships that she places in small sacks made of goat skin 7/

Son and mother get into a heated argument because he cut open one of the sacks out of curiosity, and all the contents spilled out. She puts him on a ship, bound England and Norway 8/

Captain goes to Denmark because he had some letters of Tycho Brahe, who lived on the island of Hven. Now we get a cameo surprise appearance of Tycho (!!) Boy goes ashore and delivers the letters to Tycho, who is pleased and asks him many questions (in Danish) 9/

Now...difficult to suspend belief but Duracotus (14 years old at the time) learns Danish and astronomy in a matter of weeks from Tycho. And he decides to stay on Hven: "These activities reminded me of my mother – in fact she had a constant habit of talking to the moon." awww 10/

After several years of learning astronomy "the most divine of sciences" Duracotus returns to his mom who is sorry to have sent him away on a ship in a fit of anger. They compare notes on astronomy (she also knows a lot). They reconcile 11/

Fiolxhilde then initiates her son in the occult art of summoning spirits (called "daemons") so he can converse with them and learn new astronomical facts. They do some wonderful witchcraft and summoning together (hmm this is SF and fantasy crossover) 12/

This is when he learns about Levania, located 50,000 German miles above the Earth "The journey to and from this island from our Earth is very seldom open; but when it is accessible, its easy for our people" - but for humans it is very dangerous 13/

Apparently, you cannot be fat, or sedentary. Best suited are "dried up old women", them, and Spaniards, for this arduous journey which takes 4 hours and described in lovely SF detail 14/

He describes in detail how "Just as geographers divide the Earth's globe into five zones due to celestial phenomena, so Levania consists of two hemispheres, the one of the Subvolvans, and the other of the Privolvans." - how the sun appears from Levania, the seasons etc 15/

Lots and lots of astronomical detail e.g., "a 19 star-year cycle or in 235 days, summer occurs 20 times and winter just as often towards the poles, and at the equator 40 times. Just as we have our months they have 6 days in all during the summer, the rest belong to winter" 16/

Some stuff on eclipses too "Because they have long days and nights, they experience most frequent eclipses of both heavenly bodies." - so all this detail is meant to show that you can do astronomy not just from Earth but that an alien species could also do astronomy 17/

that opens up the dazzling possibility of aliens doing astronomy all across different parts of the universe. Kepler hereby shows that by pushing the Earth from its center, the Earth loses its central position and becomes just a planet. Once you do that, the world becomes vast 18/

Oh and it ends with "this was all a dream" (oldest trope ever, but I assume not when Kepler was writing
"I came back to my senses, found that my head was on a cushion and my body wrapped up in a blanket." 19/

You can read an entire translation of this story here https://frostydrew.org/papers.dc/papers/paper-somnium/
I am tagging @ericlinuskaplan @eschwitz @CChrisrose -- who might be interested!