At 3.48am next Tuesday the double-star will be blocked by the moon, an event called a lunar occultation. It will reappear from the dark side of the waning crescent moon at 4.49am.
They were a fairly common event, but it was rare to have the chance to see one visible without a telescope, Dunedin Astronomical Society life member Ash Pennell said.
Traditionally called Zubenelgenubi, the pair of stars orbited each other, appearing as one extra bright star and the brightest in the Libra constellation.
It was also called Alpha Libra, which included its designation as an alpha star.
Stars were ranked in brightness in descending order in the Greek alphabet, meaning Alpha Libra was one of the brightest.
It had been "a good few years" since an alpha star had a lunar occultation, he said.
You had to be in the right time and the right place to observe it, making it an exciting event for enthusiasts.
What made it particularly special was that people could easily observe it from home.
Seeing it with the naked eye would be a challenge, but using binoculars would be a great advantage and a small telescope would be ideal.
People who were really keen were welcome to come to Robin Hood Park, where the Beverly Begg Observatory would be open and telescopes would be available outside for use.
