Tellisian mains voltage is 180 volts AC, 50 Hz. Yep, they all agreed on a standard together.
(It helps when the three major countries exist on the same continuous landmass)

The two Tellisian moons don't actually orbit each other despite usually being depicted in close proximity.
The orbital period of Fen (the nearest) is about half that of Yor (the furthest). This makes it possible for Fen and Yor to be visible in the sky within a few degrees of each other multiple times per day.

Corona's three moons are on more distant orbits than Tellis' moons.
"A" is very prominent in the sky (and very red), the other two ("B" & "C") are much further. "C" is icy but habitable.

B1257+12C ("Cucaloris") has no moons, not that they would be visible from the surface anyway.
"Chthonian Sea Level" is defined as the elevation of points on land that are about 100 miles above the lowest point on the surface. Below this point, atmospheric pressure increases tremendously, and layers of wildly varying temperatures and densities form as different components of the atmosphere condense, boil, precipitate and freeze at different pressures and temperatures. These layers constantly interact in a manner similar to the atmosphere of a gas giant but on a smaller scale and geographically-confined.
Despite the storminess, the seas can be crossed by even rudimentary airships since air at habitable altitude is much less dense than the layers of air directly above the sea. The use of simple sails to traverse the seas has been known since the beginning of recorded history and may have influenced early writing.

B1257+12C was at one point a gas giant, but lost its outer atmospheric layers. Still, the remaining atmosphere is so thick that a substantial portion of the visible light at the habitable surface is actually created by secondary emission and aurorae at higher altitudes. The rotational period is 6 hours.

Aurorae on B1257+12C are bright enough to be comparable to Earth's twilight in terms of illumination of the surface, at higher latitudes, they can become even brighter. Magnetic storms usually cause larger variations in brightness than normal. The region above the "arctic circle" and below the "antarctic circle" experience seasonal brightness changes that are so extreme as to be completely uninhabitable. Heat generated from the combined brightness of aurorae, secondary emission, pulsar light and the slightly thinner atmosphere is difficult to measure. There are no ice-caps, but other "orderly" atmospheric phenomena are known to happen at these locations which are believed to have some commonalities to atmospheric phenomena at the polar regions of gas planets.

B1257+12C experiences magnetic storms due to the very powerful planetary magnetic field (3 Tesla) and pulsar wind.

B1257+12C will erase magnetic media easily. Early tape and disk storage was achieved with bi-stable photo-sensitive media similar to film. Formulations usually toggled reflectivity and transparency when exposed to either higher or lower wavelengths of light.

Nachtan have trouble differentiating colors of longer wavelengths than green. This is because their eyes don't use a system analogous to a single optical lens and sensor, but instead use collimators and prismatic crystals which actively "dissect" an image rather than receiving signals from fixed "pixels" reactively. As a result, a point of a longer wavelength of light takes longer to "find" proportionally to the length of the wavelength so that Red, Orange, Yellow and Green things tend to more easily blur and seem to have less "resolution" than Blues, Violets and near-UV bands. This is part of the reason they have so many eyes (wider field of vision means more time to evaluate longer wavelengths on moving objects), the other being that image-dissecting is relatively noisy and susceptible to distortions and having more eyes means more samples to "clean up" the image.

Tellisian records are recorded at Continuous Linear Velocity, so if you play them on a record player from Earth, the music becomes progressively slower as the stylus tracks inward. Why? Because such a system utilizes a simple CVT (two gears and a spring, easy to make) which allows for a simple all-mechanical playback speed adjustment mechanism that looks like an "added feature" to the consumer even though it's just some levers to set the pinion "start and stop" positions for the angular tracking. The biggest disadvantage was that the spacing between the two pinion stops was crucial for keeping the playback speed correct all the way through, and with the very tiny size of the CVT (about an inch of travel), this meant that temperature and material actually impacted the consistency of playback speed. The biggest advantage was that the record had the same potential sound quality for its entire play-length, which is not the case for ordinary Continuous Angular Velocity playback. But really, it's just another case of "Furries do it differently".