When King Harold the Second of England headed toward a showdown with William the Conqueror in the year 1066, many of his people thought he was doomed. A bright comet had blazed across the sky earlier in the year. That was a sign of serious bad luck. And when Harold lost, the comet was depicted on a famous record of the battle — the Bayeux tapestry.

Comets are balls of rock, dirt, and frozen gases. When they get close to the Sun, some of that material fizzes off into space, forming a long tail.

Yet that profile wasn’t understood until recent centuries. Before that, anything in the night sky that changed was thought to be bad news. And because comets were prominent, they were thought of as messengers from the gods — or from demons. They inspired fear, and were considered bad omens.

Halley’s Comet has appeared in the night sky many times. And it’s been quite bright during many of those apparitions. So it’s received a lot of the bad press. It was blamed for earthquakes and the birth of two-headed animals in Switzerland, the Black Death in England, and the fall of the Alamo in Texas. And in 1910, people bought “comet pills” to protect them from its gases.

Comets can be scary — but only if they hit Earth. In 1910, a comet may have flattened hundreds of square miles of Siberian forest when it exploded high in the sky. But such encounters are rare. Most comets are nothing to fear. They’re beautiful objects that just happen to be passing our way.

More tomorrow.

Script by Damond Benningfield