Comet C/2025 R3 PanSTARRS hangs over the western horizon for one week, then vanishes for 170,000 years
If you have a clear western sky and an hour to spare after sunset this week, you can look at something no other human being has ever knowingly seen. Comet C/2025 R3 PanSTARRS, a frozen visitor from the deepest edges of the solar system, is making its only appearance over New Zealand for roughly the next seven days before it loops back into the dark and disappears for around 170,000 years.
The comet was first spotted by the Pan-STARRS survey telescope on Maui in 2025 — its name follows the convention of tagging discoveries with the year and the catalogue number — and astronomers quickly worked out from its trajectory that it had come from the Oort cloud, a vast spherical shell of comets that surrounds the Sun at a distance roughly 2,000 to 100,000 times further out than Earth. Most Oort cloud comets sit out there for the entire age of the solar system without ever being disturbed. Every so often, a passing star or a wobble in the galaxy’s gravity nudges one inward, and it falls toward the inner solar system on an orbit that takes hundreds of thousands of years to complete. PanSTARRS is one of those.
For New Zealand viewers, the practical instructions are simple. Find a spot with an unobstructed view of the western horizon. Get there in the hour after sunset. Look low above the western sky in the gathering twilight. Stardome astronomer Josh Aoraki told RNZ that “anywhere in the country is going to get a good view,” though the West Coast of the South Island is particularly well placed because the sea sits exactly where you want the horizon to be — flat, low and unobstructed by hills or buildings.
That last point is worth taking seriously. Comets on their way out of the inner solar system spend a lot of time low to the horizon, and a single ridge or a row of houses in the wrong place can ruin the view entirely. If you live anywhere with hills to the west — most of Wellington, Dunedin, the Hutt Valley, the Hauraki Plains — it is worth driving twenty minutes to somewhere with an open western view. A west-facing beach, a cliff above a harbour, the seaward side of a coastal park, anywhere the sun was actually visible at the moment it set. Even a low fence or a tall tree at the wrong angle can be enough to mask a comet that is only a few degrees above the horizon.
Light pollution matters too. From the centre of Auckland, Christchurch or Wellington the contrast is washed out by streetlights and you may need binoculars to find anything at all. Drive ten or fifteen minutes out into a rural pocket — the Awhitu Peninsula, the Port Hills, a Wairarapa back road — and the comet should be visible to the unaided eye if the weather plays along. The MetService forecast is the second thing to check after the sunset time. A solid bank of cloud out west turns a once-in-civilisation event into a quiet drive home.
What you are actually looking at is worth dwelling on for a moment. A comet’s nucleus is a chunk of frozen water, methane, ammonia and dust, usually a few kilometres across, that has been sitting at temperatures close to absolute zero for the entire 4.5-billion-year history of the solar system. As it falls in toward the Sun, the surface ices begin to vaporise and the comet grows a coma — a glowing halo of gas and dust around the nucleus — and a tail that streams away from the Sun for hundreds of millions of kilometres. The tail you can see from a Taranaki beach is sunlight scattering off particles that were locked in ice longer than the Earth has existed.
The 170,000-year orbital period is the genuinely staggering part. The last time C/2025 R3 PanSTARRS came this close to the Sun, anatomically modern humans were not yet leaving Africa. Neanderthals were still the dominant hominid in Europe. The next time it returns, give or take a few thousand years, no one alive today will have living descendants in any meaningful sense. This week is the only week any human ever gets to see it.
Newswire has a related tool that is worth pairing with a comet hunt — The Cosmic Zoom pulls back from Earth through 26 orders of magnitude to the edge of the observable universe, and it gives a useful sense of where the Oort cloud actually sits on a scale that matches the rest of the cosmos. The Oort cloud is roughly halfway out to the nearest star, which is to say PanSTARRS has been falling toward us for the better part of a million years.
If the weather forecast looks rough this week, the backup is to get out as soon as a clear evening shows up. Each night the comet’s position shifts slightly, but the same instructions hold — west, low, an hour after sunset. Bring binoculars if you have them. Bring patience if you do not.
Did you spot it from your part of the country? Drop a comment below and tell us where you watched from and what you saw.