Brightest night

(You could be looking for the book of the same name or the graphic novel instead. This article refers to the actual night.)

The brightest night occurs when all three moons are full, which happens about every one hundred years. Not much is known about this rare phenomenon.

According to the NightWings, in relation to special NightWing powers, a NightWing dragonet born under one full moon grants prophecy telling, a second full moon gives mind reading, and the third was originally believed to gift animus magic until it was later proven that animus magic is transferred genetically. Now, it is believed that the third moon enhances the powers of the other two moons. This means that during a brightest night, any NightWing dragonets that are born have both mind-reading and prophecy powers that are all enhanced. 

Battlewinner and Morrowseer came up with the Dragonet Prophecy to find a new home. The dragonets of destiny were born on the most recent brightest night, before the events of the main series. However, as Darkstalker later states, if Starflight had hatched under all three moons, he would have the same powers that Darkstalker did. Sunny, too, might have had those powers, as Darkstalker received powerful mind-reading and foresight from the three full moons despite being half IceWing, which shows that NightWing hybrids can also have powers.

History

Foeslayer stated during a brightest night that there had not been any thrice-moonborn dragonet in generations, indicating that no NightWings hatched on the previous brightest night, since dragons can live well past a hundred years old. Darkstalker was born on a brightest night. By using his power of foresight and animus magic, he could have made it so that his sister Whiteout hatched with him, but Darkstalker chose not to.

Next Brightest Night

During the events of The Brightest Night, there appears to be a second "brightest night", many decades before the next one should have been. This was caused by two full moons and a comet passing very close by the planet. Fatespeaker predicted that the comet would kill everyone in Pyrrhia. This did not happen. Instead, the comet caused minor earthquakes, one of which snapped the moonstone bracelet enchanted to keep Darkstalker in his eternal slumber. So, Fatespeaker was pretty close about the world ending. The next true Brightest Night would be about one hundred years after the one the dragonets hatched on. The specific date for the next brightest night would be around 5,106 AS.

Trivia

• It is mentioned several times throughout the series that Clearsight may have thought of the brightest night as a curse, because of the powerful NightWings that could hatch from it like Darkstalker.
• Starflight is the only known full NightWing to hatch on the brightest night and not have any powers. This is likely because he hatched underground, away from the moonlight, as the guardians were unaware that it would gift him powers.