Clouds rolling in at 5am this morning blocked the precise moment astronomers in Auckland had been waiting for - the dwarf-planet Pluto fleetingly passing in front of a far-flung star.

The eclipse-like phenomenon, known as a stellar occultation, took just minutes but thick cloud in Auckland blocked the view for New Zealand and American scientists who had stayed through the night to witness it.

Stardome Observatory astronomer Grant Christie said it was "disappointing" the team was clouded out.

The data was still being analysed to see whether any of the occultation could be seen through the thick cloud.

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A team from Massachusetts Institute of Technology had flown to New Zealand and were stationed at the Stardome overnight to record the phenomenon.

"They were obviously disappointed. We're all disappointed after working hard to prepare for three days and in their case coming from overseas," he said.

"Cloud sort of messed us up at the end after three days of preparation, but that's the nature of it. That's why we have lots of people in lots of different places. For an event that's occurring at a particular time and you'll never see it again it's essential to have lots of different eyes looking."

Nasa plane Sofia had the advantage of being above the weather and would have recorded some important information, he said.

But the plane itself would only have given scientists one part of the jigsaw puzzle and information was needed from observatories around the country looking at Pluto's atmosphere from different angles, he said.

The data collected will inform the data recorded from Nasa spaceship New Horizons which is due to reach Pluto in about two weeks.

Mr Christie said any information New Zealand observatories could feed through to the spacecraft's team would be helpful.

"The more you can learn about the state of Pluto before the spacecraft gets there the more use the spacecraft's data will be," he said.

"And they're also at the stage they can make course corrections to the spacecraft, they have different choices as to which course they're going to choose. Observations from these occultations will help them make those decisions."

A stellar occultation led to the discovery of Pluto's atmosphere back in 1988 - and the rare events yield important scientific data whenever it occurs.

The last time this happened was 2006 when significant discoveries about Pluto, including its many moons, were made from just a few seconds of exposure.

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