It was on this date nearly 1000 years ago that a sight was first recorded as appearing in the sky that was interpreted as an omen of both fortune and doom. The date was March 23, 1066 and the sight: a comet, now known to be Halley's Comet.
Despite its orbit of 76 years, it is the appearance of 1066 remains the most famous for the reason that it was depicted on the famous Bayeux Tapestry, which depicted the Norman conquest of England at the Battle of Hastings, which took place on October 14, 1066. In addition to scenes of the battle, including England's Harold II taking an arrow to the eye, the intricately woven cloth also depicts the comet blazing overhead.
At the time, comets in the heavens were seen as isolated events (it was not until the 1600s when Edmond Halley realized that his now-namesake comet was a returning visitor) and, with the superstition prevalent at the time, often interpreted as omens for events here. While it is not recorded what England's then-ruling Anglo-Saxons thought of the comet, William, Duke or Normandy and later 'the Conqueror,' interpreted the comet as an omen of success.
While we now know that the comet had nothing to do with the success of the invasion, here's an interesting historical bit of trivia to consider: 1066 marked the last successful invasion of England.