Take a look out into the sky early tomorrow morning and you might see a moon that looks as if it's been dipped in red ink.

A partial lunar eclipse is happening in the early hours of Tuesday morning as the Earth travels between the sun and the moon and casts its shadow on the lunar body.

Its expected climax at about 6:20am would show the moon with a red tinge across part of its surface.

Director of Otago Museum, astronomer Ian Griffin said it was only a partial eclipse so wouldn't be as dark as a full one, but would still be quite "fascinating".

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"About a quarter of the moon should go a reddy colour or will certainly go dark and that's because the shadow of the Earth is on it."

Griffin said the eclipse was a result of the Earth's shadow being cast on the moon.

"During a lunar eclipse the Earth comes between the sun and moon and cuts off the light."

He planned to get up at about three to see the eclipse begin, but said most people would likely only see something across the moon's surface from 5:20.

By 7:20 it would be all over as the moon began to set.

Griffin said as long as you can see the moon the eclipse would be visible ... "as long as clouds aren't in the way".

The MetService said there was a fair bit of cloud around but indicated the best chance of a clear sky would be in Canterbury or the Hawke's Bay.

The next partial lunar eclipse was not expected to arrive in the country till late July next year.

A total eclipse, where the whole moon was cast in the Earth's shadow, was also expected early in 2018.