Discovered in Hawaii

Comet C/2025 R3 (PanSTARRS) was discovered on September 8th, 2025, in Hawaii using a 2-meter telescope as part of the Pan-STARRS (Panoramic Survey Telescope And Rapid Response System) observation program. In the images taken at the time of discovery, it was located in the constellation Pegasus and had a very low brightness of approximately magnitude 19.8. At the time of discovery, it was thus approximately 400,000 times fainter than objects at the limit of visibility to the naked eye. In the images, it showed only weak cometary activity, namely a blurred nucleus without a distinct tail. However, by mid-March of this year, it had become visible to the naked eye through small astronomical telescopes, and its trend of brightening continues steadily.

For the first time near the Sun

The comet’s orbit indicates that it is a so-called long-period comet from the Oort Cloud, passing through the Solar System for the first time and likely to be gravitationally ejected into interstellar space after its passage. It will therefore most likely never return to the Sun after its next perihelion. It will pass through perihelion on April 19th 2026, at a distance of about 0.5 astronomical units (half the distance from Earth to the Sun, about 75 million km), and less than a week later, on April 26, 2026, it will pass closest to Earth at a similar distance (about 73 million km). At that time, however, we won’t be able to see it; it will appear in the daytime sky at an angle close to the Sun. After passing through the Earth’s vicinity, it will move to the southern hemisphere, where observers there will be able to track it with telescopes for about another month.

Only two weeks of visibility

Since the comet is moving steadily from the northern sky to the southern sky, we have a limited window of time to observe it. It will be visible for only the next two weeks, roughly until April 21th 2026, during the early morning hours before and during dawn. The best time to observe the comet is to get up at 4:30 a.m. CEST, when it can be found above the east-northeast horizon in the constellation Pegasus, in the area known as Pegasus’s Square. Each day, the comet will be slightly brighter but closer to the horizon and harder to see against the sky illuminated by dawn. It will be particularly difficult after April 19th. Observers using binoculars might also mistake it for the Andromeda Galaxy, which will be significantly higher above the horizon and further to the northeast at that time. We therefore recommend using the attached map to locate the comet.

Given the current trend of brightening, experienced observers should be able to spot it with the naked eye after April 10th; however, we strongly recommend using at least binoculars for observation, as they will make it easier to see both the comet’s nucleus and its “feathery” tail.

You can try to take a picture of the comet

To photograph a comet, you’ll need, above all, a location with an unobstructed view from the east to the northeast and a dark sky away from city lights. You’ll need a tripod, a camera capable of long exposures, and a fast lens with a focal length of 24 mm or longer—so that the comet’s head and at least a hint of its tail stand out in the photo. Locate the comet using a map, focus your lens, and set the ISO high enough to avoid noise while keeping the exposure long enough (several seconds) so that the stars do not stretch due to Earth’s rotation. The comet’s head will appear small and strikingly greenish-blue in the image. You can even capture a comet this way with a well-equipped smartphone. But don’t expect images with details in the tail or the comet filling the entire frame—such shots require telephoto lenses or telescopes mounted on special mounts.

Solar activity and the comet's tail

While the comet’s bright nucleus is already easily visible through small binoculars and will grow brighter in the coming weeks, the comet’s tail is faint, visible only in images, and changes frequently. This is due to the interaction of the gas in the tail with the solar wind, which is currently highly variable because of high solar activity. In the images, the comet’s tail thus exhibits various folds, streams, knots, and breaks caused by the direct exposure of the gas in the tail to the invisible stream of charged particles in the solar wind. It looks as if the tail were billowing like smoke from a chimney in the wind.

Comet PanSTARRS is one of many fascinating phenomena that we will be able to observe in the Czech Republic throughout 2026. You can find the complete list of the most remarkable celestial events to look forward to on this page.

Kontakty:

Mgr. Petr Horálek

RNDr. Tomáš Gráf, Ph.D.