There is a theory that suggests many UFO sightings are caused by
volcanic and
tectonic pressures under the ground. These (apparently) can cause
electromagnetic discharges in the
atmosphere that can look like
hovering balls of light.
One well
documented case of this was in
New Zealand, where a
glowing ball was seen on several occasions, moving
north. This theory would make sense, since the whole country is basicly teetering on the edge of what has been imaginatively named the '
ring of fire', and has had more than its share of earthquakes and volcanic
erruptions.