Source: Explorer's Guide to Wildemount

Wondrous item, legendary (requires attunement)

Used to summon night, this 6-inch-diameter, jet-black orb is cold to the touch. You can spend 10 minutes to activate it, causing the area within 10 miles of it at the moment of activation to become night even if it is daytime. This night lasts for 24 hours, until you cancel it as an action, or until your attunement to the pearl ends. Once used, the pearl can't be used again for 24 hours.