Otago Museum director and astronomer Dr Ian Griffin told Morning Report that the planets Jupiter and Saturn would get remarkably close over the next couple of nights.
"They are going to be so close together, you won't be able to separate them ... you'll need binoculars and a telescope to split them, and this is something called a conjunction."
Jupiter and Saturn come together roughly every 20 years, "that's nothing particularly special", he said, but "to get this close together in the sky is incredibly rare".
Griffin said some astronomers' calculations suggested the two planets had last been seen this close back in 1226.
"And you're not going to see them this close together until the year 2080."
To spot the planets, he said: "Go out tonight, find the moon, and then look down to the left and you should see a bright star and that is Jupiter and Saturn.
"Then if you point your telescope or even a pair of binoculars at that bright star you'll see there are two planets - Jupiter and Saturn with its wonderful rings.
"And you if look really carefully you'll see ... four of Jupiter's moons and one of Saturn's. It will be seven planetary bodies all in that one field of view."
It is called the "Star of Bethlehem" because "in 7BC there was a conjunction between Jupiter and Saturn, and back then the 'wise men' were astrologers and this would have had some significance to them" - and it was mentioned in the Bible as well.
Griffin said anywhere with clear skies tonight and tomorrow night would make for perfect viewing, ideally looking towards the southwest.
"They disappear by 11.15pm, so you need to be out just after sunset - [until] about an hour and half later."
Griffin will be at the Mt John Observatory in Tekapo to view the conjunction of the planets.
- RNZ
