New Zealanders looking to the sky on Friday night will be treated to an incredibly rare lunar spectacle, not seen in their sky in more than 800 years.
The longest partial lunar eclipse visible in New Zealand since the year 1212 is set to start at 8.20pm NZT, when the shadow of the Earth will begin to move across the moon’s face. It will be 97% covered with shadow by 10pm. At that moment, the lunar surface will briefly turn red. The near-total eclipse will finish its three-and-a-half-hour journey just prior to midnight.
Rob Davison, an astronomer at Auckland’s Stardome Observatory, said: “When you have a total lunar eclipse, it’s not uncommon to have the entirety of that lasting for three-and-a-half hours, sometimes a bit shorter, sometimes longer. But for a partial eclipse to last this long, it’s just very rare.
“Most of the eclipse will be dominated by the shadow moving across the moon, with a brief period where it will appear as a blood micromoon in our night sky.”
There are two main reasons this is a rare event, he said, the first being that it is a partial eclipse, but also because of where the moon is positioned in its orbit.
“The moon is at apogee, which means it’s at the farthest point from Earth in its orbit. The moon’s orbit around the Earth is not a perfect circle, it’s an ellipse which means as it goes around, it comes a little bit closer and then, as it swings around, it goes a little bit further away,” Davison said.
“So when it’s at its closest point, it’s called perigee, and that’s when you get a so-called super moon – about 360,000 kilometres away. When it swings around to the other side, and is in apogee, it’s about 400,000 kilometres away.”
The moon moves slower at this point, and this is why there is an ‘“unusually long” partial-eclipse.
The eclipse will be visible in other parts of the world, particularly in the western states of the US. But for New Zealanders, this eclipse is made all the more special because it happens at a time of night when stargazers are more likely to be awake, Davison said.
New Zealand will have 13 total or near-total lunar eclipses in the next 20 years. But seven of those will be in the early hours of the morning. Four will be visible around midnight. “Only only two of them will be in the evening, including this one,” he said.
“So for people aren’t really wanting to stay up late, or if they have families or younger children, this is a really good one to do.”
For the curious, or those who cannot catch a glimpse, Nasa will livestream the event.