Iltani the Blue was the second moon of the Nerath world. The first one is simply "the moon", though some people call it Sehanine, as the goddess. Iltani didn't always existed in the Nerath world, as the gods only created one sun and one moon at the dawn of time. Iltani appeared one night, in CY -130, from nowhere. Its appearance sparked consternation because no one had foreseen the arrival of a completely new moon. Soon, however, it became popular among the common people, gaining a reputation of being a good omen when it was viewed waxing full, especially by travelers and explorers.
Some did not take the moon for granted, though they were fascinated by the moon’s appearance and dedicated themselves to learning the truth. One of these people was Tetherya Acrid, a tiefling sorceress already fascinated by celestial objects, believed the appearance of the blue moon must presage something amazing, even if what that might be wasn’t immediately obvious.
Tetherya spent years putting together an expedition to Iltani (this is interesting, because it means a canon mention of a Spelljamming mission in the Nerathspace), but the expedition took many years to complete because always something happen that halted the travel. Tetherya didn't surrender, though, and eventually set her spelljammer to the blue moon.
She found the entire moon was a 500-mile diameter chunk of a beryl-like mineral. Airless and dead, the sorceress discovered nothing on the light side that faced the world. On the dark side, Tetherya found massive runes inscribed as deep fissures in Primordial. The runes seemed to be a warning. According to the tiefling, the message read:
"You are barred from this world, apocalypse. You will have no landing here, Nebiru. Iltani the Blue is set in the sky against you, Falling Star. While Iltani guards the heavens, your red scar shall not be scratched across the night. This world rejects you, Nebiru, in the name of Iltani the Blue."
Tetherya found nothing else on the moon except for the warning. She returned to the world and researched the name Nebiru the Falling Star. She discovered Nebiru was as an apocalypse dragon (a catastrophic dragon that has lived too long and grown too powerful). According to the lore she unearthed, Nebiru resides in a vault of empty space beyond the world, in a lair of lightless hollows composed of half-formed worlds and the rubble of creation. The hollows beneath Nebiru’s airless surface are filled with the detritus of failed empires, dead kings, and broken dreams pilfered from the world. One day, Nebiru will nudge the trajectory of her moon-sized lair just so. When that happens, its path brings it into conjunction with the world. Then, the skies will flame red as her lair impacts the land with all the energy of a falling star.
This fate would take place but for one fact: Iltani the Blue served as a ward against that very possibility. As long as Iltani showed its blue face over the world, the world would be safe from that particular ending. Thus, on the day that Iltani the Blue detonated and shattered into a million fragments that rained down across the world in CY -100, Tetherya knew the world’s eventual end was assured.
Tetherya founded the Moon Catchers to found the fragments of Iltani across the World and the void between worlds. Eventually, they intend to reassemble those shards and place the moon again in its guardian position high above the world. Before handing off the reins to individual cells, she made a prediction: “One day, the blue moon will return.”
Do you remember those crazed star pact warlocks I mentioned in other topic? Well, the Moon Catchers are at odds with those madmen, as they wanted to haste the awakening of Nebiru. This is why I say spelljamming in Nerath is for the really fool or the really brave. Far Realm-corrupted stars and their aberrant spawn, two evil, sentient planets traveling the void (Allabar and Atropus), and now an apocalypse dragon...
This is all from the article "Guilds and Groups: Moon Catchers" from Dragon 382. The article don't mention who created Iltani and why exploded one day without warning, and what kind of consequences that event brought to the world beyond the threat of Nebiru. I guess, that was left to DMs to fill it whatever they wanted.
Here is the only image of that article. I presume the tiefling is Tetherya and the moon is Iltani.