Astronomical Alignment

The Astronomical Alignment is a very rare event in which all of the 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. One occured during the course of Ultima VII.

Description
The astrological alignment happens only once every eight-hundred years, and it is said to be an event of great mystical significance, weakening the borders between the planes and allowing for great acts of magic to transpire. 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. At the time of the Avatar's first quest against the Guardian, an impending alignment was to activate the functionality of the red titan's intended gateway to Britannia - the Black Gate - which was to become operable at the exact moment the planet's aligned.

The Avatar was first made aware of the alignment by brion in the Observatory, who gave the hero an Orrery Viewer to watch the orrery and planetary movements. The Time Lord later revealed the Guardian's plans with the alignment. Fortunately, the hero thwarted the Guardian's plans by using a magical transmuter to destroy the blackrock used in the gate's construction, rendering the portal useless at the moment of the alignment, thus halting the evil entity's effort to invade Britannia at that point in time.

Trivia

 * Since the game is event-driven, the planets only change position each time one of the generators is destroyed. They also don't move into final position at the end of the game, despite it being logical from them to do so.