He said observing a bolide - the name given to an extremely bright meteor - was like winning a lottery. They rocketed to Earth regularly but were observed rarely.
While he expected the fireball was indeed a space rock, as displayed by its brightness, he felt there was still a chance it could have been a piece of wayward space junk.
This was because of reports the object was moving north to south across New Zealand - a path that lined up with the pole to pole orbits of spacecraft.
Other experts also predicted the object was a bolide, probably once knocked off an asteroid during a collision.
"These fragments are circulating in the solar system and occasionally they drift into the path of the Earth," said Stardome astronomer Dr Grant Christie, who saw the powerful flash.
"But without having a piece of it, you can't really say which asteroid it got broken off."
David Britten, astronomy educator at Stardome, said witness reports were consistent with meteoritic material or space rocks entering the atmosphere.
Loud booms following a bright explosion often occurred when such material entered the atmosphere.
"It's a bit like watching fireworks in the distance. It takes quite some time for that soundwave to reach the ground. It would seem to indicate meteoritic material."
About 45,000 meteorites have been recorded over Earth with just over 1100 being seen falling.
Dr Christie said the last comparable event in New Zealand was on July 7, 1999, when a meteorite detonated over southern Taranaki with an equivalent energy release of 300 tonnes of exploding TNT.
But he said last night's event probably only packed the power of tens of tonnes of TNT.
A 2002 study in the journal Nature found that hundreds of objects roughly 50cm in diameter and packing an energy equivalent to 100 tonnes of TNT hit the Earth every year. Professor Easther expected Wednesday night's meteor had been in this size range.
"Really big events with an energy similar to the largest nuclear weapons ever tested occur much less often; maybe once every 10,000 years."
Cosmic spectacle
• Fireballs or "bolides", according to Nasa, are exceptionally bright meteors that are spectacular enough to be seen over a very wide area.
• The objects are generally fragments of asteroids or comets and orbit the sun before they finally collide with Earth. Those that cause fireball events can exceed 1m in size.
• During the atmospheric entry phase, the object is slowed and heated by atmospheric friction. in front of it, a bow shock develops where atmospheric gases are compressed and heated.
• Some of this energy is radiated to the object causing it to in most cases break apart, according to Nasa. Fragmentation increases the amount of atmosphere intercepted and so enhances ablation and atmospheric braking. The object disrupts when the force from the unequal pressures on the front and back sides exceeds its tensile strength.
• Wednesday's bolide would have been travelling around 144,000km/h, estimated Noel Munford of the Palmerston North Astronomical Society.
• About 45,000 meteorites have been recorded over Earth - of which just over 1100 have been seen falling.
• Auckland astronomer Dr Grant Christie expected the fireball had an equivalent energy release of tens of tonnes of TNT.
