Astronomical Alignment

The Astronomical Alignment is a very rare event, happening only every 800 years. It is the moment when all planets of the Britannian Solar System, including Britannia and its two Moons Trammel and Felucca, are all aligned in one straight line to the sun. It is said that this weakens the borders between the planes in a strong way.

In Ultima VII, the Astronomical Alignment played a major role. It was during the Alignment when the Black Gate would have started working, allowing the Guardian to enter Britannia to conquer the land. Thankfully, the gate was destroyed just in time by the Avatar to prevent this disaster from happening.

Trivia

 * In-game you can wait as long as you want. Even Seconds before destroying the gate, the Orrery Viewer shows you that the alignment isn't happening yet.
 * Taking the Britannian Calendar into account, the Alignment can only happen during a double new moon, which only happens at the first of a month.