Who was the first Science Fiction author to be honored in real life by having a celestial body named after them?
Asteroid 1134 Kepler, discovered in 1929 by Max Wolf, was named after Johannes Kepler, on the occasion of the 300th anniversary of his death, in 1930; see Lutz B. Schmadel's Dictionary of Minor Planet Names. Kepler's Somnium (The Dream) is considered by some (Asimov, Sagan) to be the first science-fiction novel. There is an English translation by Edward Rosen.
The runner-up to Kepler is the Russian scientist and writer Konstantin E. Tsiolkovsky; the asteroid 1590 Tsiolkovskaja, discovered in 1933 by Grigory Neujmin, was named in his honor, according to the International Space Hall of Fame.
Also of note is Jules Verne, who's had a large impact crater on the moon named after him in 1961.
The definition of what is science fiction has a lot of room for interpretation. In an attempt to take this to the extreme in order to find an extreme answer, I've determined that by some interpretations of what is SciFi you can put most celestial bodies known before the telescope into the category of SciFi characters. Also, if you take the stories as given, at least one of those characters from one of those stories was actually the author of his own myth. This would move the date of the first occurrence back several millennia to around 2500 BC. Here is the evidence that I've found ...
Firstly, if we want to get beyond a few centuries back we'll need to find a definition of SciFi which allows for REALLY ancient writers. That should be doable. According to this wiki page many others see this the way I do:
... the [science fiction] genre's roots in early fantastical works [can be traced back to works] such as the Sumerian Epic of Gilgamesh (earliest Sumerian text versions c. 2150-2000 BCE)...
That's really old! Is it really SciFi though? Unfortunately, at the time of this writing no word for 'science' existed. The book (tablets) begin with a collection of six short stories as told through the generations by the priest class (the stories cover the life of Gilgamesh from birth until his death). The book proper is actually a very long poem which may have had rhyme or meter in the long lost spoken language which it was originally written in but in English that has completely been lost (of course). The stories say that they were originally told by the main character of the story (which is actually very funny; because if he did write it then Gilgamesh is certainly his own biggest sycophant).
These myths are attempts at explaining natural phenomena and (just like SciFi) the conclusions are not always based on observed phenomena. While it is easy to say that this isn't science, the differences between these stories and SciFi isn't as cut and dried to say the least. BTW, just because a story is folklore (another Genre) doesn't mean that it isn't also SciFi. IOW, genres are not exclusive to each other which is why I would label this story as 'Folk(lore) SciFi'.
Many of the same myths have also been later incorporated into other religious texts (such as the Bible) but at the time of the original writings they were just pagan stories which featured gods; they generally weren't meant to be written by the gods and the details of these stories changed from teller to teller and each city had it's own variations of these stories.
One of the reasons that this particular mythology is very hard to distinguish from SciFi is that, in the story, Gilgamesh is 'experimenting' with various ways to defeat death itself and to a certain degree he actually achieved it. He may not be calling it the scientific process and the outcome may not be rational but it is his approach to the problem that makes this much more like science than many other stories of the age. Not to mention that the quest for immortality is still a common theme for SciFi literature.
At this point, you either believe me, know this to be true for yourself, disagree, or you want to go read the story and decide for yourself. If you disagree then let me know why below but I'm going to move on to the other half of this puzzle now; which is whether anything in the sky was actually named after Gilgamesh.
In one sense, if you are familiar with the story and you agree that the story of Gilgamesh was SciFi then the answer to this question is already clear. This is because the story of Gilgamesh is about a king trying to defy death and in doing so he was placed in the heavens by the gods as a constellation forever cursed to toil with his greatest enemy, Taurus. You may have already guessed this but that makes Gilgamesh the constellation we today call Orion. The Sumerians actually called the constellation Uru An-Na, meaning light of heaven and that was in direct reference to Gilgamesh.
If you aren't aware, the Minoans were the precursors to the Greeks and they are one of the many tribes who presumably adopted these stories and modified them to better fit their own society. Unfortunately, the story of Orion and the story of Gilgamesh do have many similarities but they also have many differences and it is hard to say with any certainty why that is the case.
Since this is a story which was already ancient when the Minoan civilization was first founded (which was at least 500 years later) it does seem a little odd that the Minoans\Greeks would rename the constellation when it is clear that they were probably already familiar with the story. This could be due to a combination of translation and divergence which would make Orion, literally, the same character (Uru An-Na => Orion; if you say those both aloud you'll hear the similarities; mix in a little dialect and this could quite possibly be the same word spoken by people of different languages). The reason that accepting this offhand is dangerous can be readily seen in the name for the enemy of Gilgamesh, the bull we know as Taurus, was called Gud An-Na, bull of heaven; I'll let you work the rest out on your own.
Now, when we think of the celestial bodies they were naming back then it is (at least to me) a little surprising to realize that they were naming most of the same types of things that we are naming today (they just had far fewer to name); the sun/stars, moon, comets, asteroids, constellations, nebula, and many of the planets have been known for 'longer than we know what we knew' you could say. In fact, most of these things already had names long before the Greeks came along and began renaming these things for themselves.
Constellations are different because they are not discrete items in the sky. We could choose any combination of nearby stars (from our perspective) and declare that as a new constellation. They are also different because it is believed that at the time of Homer there were only a few constellations which people identified and as far as I can tell most of those actually came from this story. Every since then, we've tried our best to keep with the ancient traditions it seems because we tend to use the Greek names for things to this day. Still, it is definitely curious that in the sky the most prominent Greek hero (Hercules) is a dim and difficult to find constellation while Orion who was a relatively minor hero in the Greek tradition has the grandest seat in the cosmos. I would say that this is most likely because the Orion constellation had already been claimed and was already well known to everyone.
Well, that's my case and you can take it or leave it. As promised, here is the complete translation.