Global aurora borealis device

The Eye was a device constructed by Minerva to manipulate the underlying calculations of existence, thus preventing the 2012 coronal mass ejection. However, when she learned Juno had been tampering with the Eye for her own ends, Minerva was forced to destroy it.

During her imprisonment in the Grand Temple, Juno repaired the device to store her consciousness, and manipulated Desmond Miles, a human with a sufficient amount of First Civilization DNA, into using it so she would be released. In the meantime, Minerva constructed a second Eye to commune with Desmond through the memories of his ancestor Ezio Auditore da Firenze, and used it for a final time to see if he would find a way to prevent the catastrophe on 21 December, 2012.

Seeing that Juno had survived and manipulated Desmond into using the Eye, Minerva warned him not to use the Eye, believing it would be better if the world endured another apocalypse than allow Juno to be freed. Desmond disagreed, activating the Eye and saving the world, but at the cost of his own life and unleashing Juno.

Reference

 * Assassin's Creed III