occurrence

While numerous cultures and spiritual movements have throughout history long attempted to commune with the dead, a séance, says Lisa Morton, author of “Calling the Spirits: A History of Séances,” is a relatively recent occurrence.

Cases of whooping cough, or pertussis, for instance, used to be rare, but are now a monthly occurrence, she said.

She once saw the aurora by eye from Lancaster city centre in red, green and purple but admitted it was "a rare occurrence".

Penumbral lunar eclipse – A more subtle occurrence, where the Moon travels through the outer part of Earth's shadow, resulting in a faint dimming.

But one of the internet-famous youngsters, Gizmo, may have just dropped by her childhood home, an unusual occurrence for an eagle of nearly six months.