Why this newly spotted comet has stargazers excited

Every few years, a comet appears that promises something extraordinary. Case in point: Comet C/2025 R3 (PANSTARRS), visible in the night sky through binoculars and telescopes right now, is already drawing comparisons to the rare “great comets” that become unforgettable sky shows.

But what makes a comet great? And does this one have the potential to become one? While astronomers say C/2025 R3 could be among the brightest comets of the year, brightness alone isn’t what makes a comet unforgettable. Here’s what to know about this potential cosmic spectacle.

What makes a comet “great”?

The phrase “great comet” might sound impressive, but it’s an informal term. Much like a “supermoon,” a “great comet” is not an official scientific classification. Instead, it’s more of a societal label, rooted in how a comet appears to viewers on Earth. In essence, great comets put on a dazzling show.

While the designation of a great comet is subjective, astronomers and skywatchers tend to agree on one key criterion: visibility to the naked eye. “My personal definition of a great comet is very simple: If you go outside in a dark location and look in the correct direction towards the comet, it will be obvious with just a glance, no searching, and no optical aids,” says David Schleicher, an astronomer at Lowell Observatory.

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Most comets never reach that level of brightness, remaining visible only through binoculars or telescopes. “Generally, a great comet only comes along every half-dozen to a dozen years,” says Schliecher. “But, rarely, one might see two great comets separated by only a year’s time or less.”

Because the term lacks a formal definition, there’s no official list. Still, a few standouts are widely recognized, including Comet Hale-Bopp (C/1995 O1), which was visible for 18 months, and the 1910 appearance of Halley’s Comet, which was visible during the daytime.

Why predicting great comets is so difficult

After astronomers spot a new comet, they quickly calculate its orbit by observing its ever-changing position relative to known objects, such as stars.

But since comets, which are comprised mostly of loosely bound bits of ice and rock, are notoriously unstable, their brightness changes frequently but without any sense of regularity.

“Maybe it is undergoing an outburst but will fade back to normal. Maybe it has never been close to the sun before, and just a bit of warming releases large amounts of dust and gas, but then it quickly runs out,” says Schliecher. He notes that brightness can also vary based on the comet’s distance to Earth (closer comets appear brighter) and the size of its nucleus (larger comets have “greater surface area from which dust and gas can be released.")

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Plus, as comets approach the sun, their icy bodies vaporize, creating long tails of gas and dust. As the comet changes shape, its brightness may vary, but it’s difficult to predict exactly how the comet will behave. In some cases, as a comet makes its close approach to the sun, it may disintegrate entirely before it has a chance to put on a spectacular show. That fate befell the potential great comet C/2026 A1 (MAPS) last week.

What we know about comet C/2025 R3 (PANSTARRS)

Since astronomers discovered Comet C/2025 R3 (PANSTARRS) in September 2025, they have determined a great deal about its history.

“It was likely formed near Saturn or Uranus in the earliest days of our solar system and was tossed out into the Oort Cloud, then essentially stored in a literal deep freeze for billions of years before recently arriving in our vicinity,” says Schliecher. “It has been traveling inward toward the sun for about 160,000 years.”

Some of the comet’s physical properties, however, remain uncertain. “The dust and gas released from the surface of the nucleus obscures the view of the nucleus itself, but the overall brightness suggests that it is less than one kilometer in size,” says Schliecher.

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That’s a smaller nucleus by cometary standards, which doesn’t bode well for the comet’s potential to become “great,” despite early buzz. Schleicher is blunt in his assessment: “It might be the brightest comet of 2026, but it certainly is not going to be a great comet. Sorry!”

That distinction—brightest of the year versus “great”—is important. A comet can outperform others in a given year and still fall far short of a naked-eye spectacle. In this case, the comet’s small size, combined with less-than-ideal viewing geometry, limits its potential.

How to see Comet C/2025 R3 (PANSTARRS)

Even under the best circumstances, Comet C/2025 R3 (PANSTARRS) will be a challenging target for observers, especially in the Northern Hemisphere.

“During much of April, it will be very low in the sky near the eastern horizon about an hour before sunrise,” says Schliecher, who expects the comet to be at its brightest from April 17 to 27. After that, the comet will continue moving south, putting it in a better viewing position for the Southern Hemisphere

For casual skywatchers, this means the comet is unlikely to become a must-see event. But then again, nature could surprise us.