3C 10 is the remnant of Tycho's Supernova, or SN 1572. Tycho's Supernova is the epoch for the modern Gymnomi Slime calendar.
Since it becomes very difficult to talk about simultaneous events that occur lightyears apart, each time I use a gregorian date to refer to refer to events that happen on Gymnome, the assumption is that the number of earth-days since the apparition of SN 1572 is the same on both planets. That is, in some sense, the epoch is the supernova itself, not just when Gymnomi observed it.
But now that I know where Gymnome is in space (64 light years away in the constellation Cassiopeia), we have a problem. 3C 10 is also in Cassiopeia.
distance to 3C 10 from Gymnome: 7935 ly
distance to 3C 10 from Earth: 7997 ly
difference of distances: 62 ly
distance from Gymnome to Earth: 64.58 ly
Earth and Gymnome are different distances from SN 1572. Like, the distance between the two planets is almost the same as the difference of the distances to the supernova.
(Also, we don't know the distance to 3C 10 to nearly the precision that Space Engine depicts. So it's not 7997ly, it's 8900±900 ly. But we're working in a fictional context where we can assume 3C 10 has a definite known distance because at some point in the future it will be visited by spacecrafts or at least become the subject of interstellar-scale parallax measurements.)
So this is kinda interesting. Basically it means that a theoretically omniscient observer on Earth in 1572 AD would see SN 1572, and then about 3 years later would observe astronomers on Gymnome seeing SN 1572. (Even though Gymnomi astronomers really saw the supernova 'first.')
So depending upon how you think of it the gregorian date could be off by about 64.58 years or by about 3 years.
But in truth in all circumstances where it actually matters, this gets handwaved away by the non-existence of special relativity in space operas.
In the standalone Gymnomi slime worldbuilding, for the most part, the gregorian calendar dates given don't actually have to match up with the gregorian calendar at all. What I call "2380" or "2335" as a convenient shorthand could actually be taking place in 4090 BC and 4045 BC, or one million and one million 45 AD. The gregorian dates are just shorthand so I don't have to use the extremely complex Omicyclic calendar, which accounts for Gymnome's horseshoe orbit.
It's only when it comes to my extensions of the world that fit it into space operas (like my INASO world, the Torchship TTRPG, or Mellanus in Star Trek) that the gregorian dates matter--and in one those cases the dates have to be changed anyway.
In the Simplified Omicyclic Calendar (this is not accurate to within a year, since the year length changes throughout the omicycle. In fact it probably isn't even accurate to within an Omicycle, since year 1 day 1 of the calendar was probably standardized to an Omen apparition rather than the apparition of Tycho's Supernova and I haven't decided yet exactly when that would be.)...
1 Omicycle = 30.5523042 Earth Years or 30 years, 6 months, 19 days, 2 hours, 10 minutes, and 48 seconds.
1 Mean Gymnomi Year = 0.784366789 Earth Years
1 Omicycle = 38.952 Mean Gymnomi Years.
So since 23-July-2026 AD is 453.7 years after Tycho's Supernova, the current Gymnomi date is roughly:
15th Omicycle, Year 34
Here are some more dates of note, again, very approximate:
Nov 1572 AD: 1st Omicycle, year 1 SN: Epoch Jul 2026 AD: 15th Omicycle, year 34 SN: Current date Jun 2280 AD: 24th Omicycle, year 7 SN: TOS movies, steam trains. Jan 2335 AD: 25th Omicycle, year 37 SN: Freight Misconductor Jan 2358 AD: 26th Omicycle, year 27 SN: Eaurp Guz birthday Jan 2381 AD: 27th Omicycle, year 17 SN: Guzcomic ~~~ 2383 AD: 27th Omicycle, year 20 SN: Stormchaser Mission Mar 3188 AD: 53rd Omicycle, year 35 SN: Discovery S3
