The sky of Ashandri

When you look up into the sky of Ashandri, many things seem similar to how they were on Virthys. At least, at first glance. During the day, the firmament is purple instead of blue, but otherwise looks pretty normal. The sky emerald is a gargantuan, almost spherical gem hovering above the world-island. During the day, it shines so bright that it looks just like the sun of Virthys did.
As its light fades in the evening, you begin to see the emerald's structures, looking like perfectly polished jewelry. As the night approaches, it turns grey. Many people call this the emerald moon. During the 24-day-cycle of each month, it turns darker and darker in the center. At the last three days of each month, it is barely more than a thin spherical line (called Sharpmoon). On the first day of the new month, the emerald moon lights up brightly (fittingly called the Brightmoon), engulfing the world in dim light. It stays like that for three days before it normalizes again. It is also during this time that lycanthropic creatures transform, and many moon-based spells work stronger.
The last five days at the end of the year, the Paragon's Feast, have their very own cycle: The first three days, the emerald moon turns ghastly green (the Ghastmoon). Some say that the activities of undead are stronger on these days, and that it is the time of necromantic magic. The next two days of the Paragon's Feast, the Brightmoon appears, and stays for the first three days of the month of Void (the first month of the year). So effectively, there are five instead of three Brightmoon days.
The stars in the night sky are the distant lights of other world-islands. The biggest difference to most worlds outside of Braythe is that they do not move: The chains keep the worlds in their place. This makes using the stars for navigation a lot easier, but other skills like fortune-telling based on the movement of stars practically impossible. Sages and sooth-sayers are learning new methods, and it seems the subtle movements of the Braythian Void clouds - barely visible at night - do offer clues about the future.
There are also a handful of reports of unusual sightings in the night sky: From strange beasts to flying ships. Many think these were just hallucinations, but some sages are not so sure.

What exactly is the Sky Emerald?

When Ashandri appeared in the Braythian Void, the sky was black, distant stars the only source of light. Suddenly, a gargantuan, roughly spherical emerald appeared in the sky. In the darkness, most people couldn't see it, but it slowly began to flare up. An hour later, the Sky Emerald was as bright as Virthys' sun had always been.
Sages of The Arcanists have spoken with Marisha Veilbreaker, and she explained that she has no idea how and where from the mystical gem appeared. She knew she could control it to a certain extent, shaping it roughly after the celestial objects of Virthys, and adapting it to the needs for the new world. But otherwise, the Sky Emerald is not under her control.
The heavenly body is far closer to the world of Ashandri than the moon was to Virthys, but visually appears to be about the same size. This means the Sky Emerald is significantly smaller than a moon, and could theoretically be reached by flying vehicles. Teleportation and gate spells trying to reach it do not work - the Arcanists have tried.
If it is possible to land on the Sky Emerald, it shouldn't be done during daytime: Its light comes from actual solar fire emitting from the celestial gem. But during night time - it could be done. Hypothetically.