With all the comet buzz this year—from C/2025 A6 (Lemmon) to C/2025 R2 (SWAN) to several other icy visitors lighting up our skies—it’s the perfect time to explore what comets really are, how astronomers have studied them through history, and how these ancient wanderers get their names.

Frozen Time Capsules of the Early Solar System

Comets are leftovers from the birth of our solar system about 4.6 billion years ago. They formed in the cold outer regions of the solar nebula, where rock, dust, and frozen gases like water, carbon dioxide, and methane clumped together. Most now reside in two distant regions—the Kuiper Belt beyond Neptune and the even more remote Oort Cloud, a vast shell of icy bodies surrounding the Sun.

From time to time, a gravitational nudge from a planet or passing star sends one of these icy objects plunging toward the inner solar system. As it approaches the Sun, its ices begin to vaporize, forming the glowing coma (the hazy envelope around the nucleus) and the familiar tails that always point away from the Sun.

Every comet that graces our skies carries material unchanged since the dawn of the solar system—a frozen archive that lets astronomers study how the planets, and even Earth itself, began.

A Brief History of Comet Discoveries

Humans have been observing comets for thousands of years. Ancient cultures often saw them as omens or “hairy stars,” mysterious and unpredictable visitors in the night sky.

The turning point came in the 17th century with Edmond Halley, who recognized that the comet he saw in 1682 followed the same path as comets seen in 1531 and 1607. He predicted its return in 1758—after his death—and when it did, the comet was named Halley’s Comet, becoming the first recognized periodic comet.

By the 18th century, systematic comet hunters were sweeping the skies, among them Charles Messier, who was so frequently frustrated by mistaking nebulae for comets that he began compiling a list of “non-comets.” His catalog, the famous Messier Catalog, is still used today by astronomers and astrophotographers to locate some of the most beautiful deep-sky objects.

In more recent history, Caroline Herschel, Jean-Louis Pons, and others discovered dozens of comets visually. Fast forward to the 20th century and beyond, and discoveries like Comet Shoemaker-Levy 9—which spectacularly collided with Jupiter in 1994—and Comet Hale-Bopp in 1997 made worldwide headlines.

And we have a special connection right here at the Denver Astronomical Society: David “Doveed” Levy, co-discoverer of Shoemaker-Levy 9, is a longtime member of the DAS and our very own Poet Laureate.

How Comets Are Named

Every comet name tells a story, and it follows a precise system set by the International Astronomical Union (IAU).

Take C/2025 A6 (Lemmon) as an example:

• C/ – The prefix indicates the comet’s type:

  • C/ = non-periodic comet (long-period or one-time visitor)

  • P/ = periodic comet (returns in under 200 years)

  • D/ = comet that has disintegrated or been lost

  • X/ = historical comet with an uncertain orbit

  • I/ = interstellar object (such as 1I/‘Oumuamua)

• 2025 – Year of discovery

• A – Half-month of discovery (A = first half of January, B = second half, and so on)

• 6 – The 6th comet discovered in that half-month

• (Lemmon) – The name of the discoverer or survey that found it

So, C/2025 A6 (Lemmon) tells us this is a long-period comet, discovered in early January 2025, and first detected by the Mount Lemmon Survey in Arizona.

From People to Programs: The Modern Comet Hunters

For most of history, comets were discovered by individual observers—astronomers scanning the sky night after night through their telescopes. Famous names like Halley, Hale-Bopp, and Shoemaker-Levy reflect that personal legacy. But the landscape changed with the rise of automated sky surveys. Today, most new comets are discovered not by human eyes but by robotic telescopes equipped with wide-field cameras and computer software that automatically detect moving objects. Because these programs involve teams of scientists and complex systems rather than a single discoverer, the IAU credits the survey or instrument rather than an individual. That’s why we now see comets named for programs like NEOWISE, PanSTARRS, and Lemmon.

Here are some of the most common modern discoverer designations:

So when you see a name like C/2025 A6 (Lemmon) or C/2020 F3 (NEOWISE), you’re seeing the legacy of 21st-century comet hunters—massive instruments scanning the heavens every night for these icy visitors.

Can Amateur Astronomers Still Discover Comets?

While modern surveys and space telescopes make most new comet discoveries today, amateur astronomers still play a meaningful role in observing and tracking these icy visitors. Every so often, a dedicated observer with sharp eyes and good timing still spots a previously unknown comet before the automated systems do. In fact, even in the age of giant survey telescopes, a few new comets every decade still bear the names of amateur discoverers.

One exciting way to join the discovery process yourself is through NASA’s Zooniverse Comet Hunters project, where volunteers help identify potential new comets in data from the ESA’s Solar and Heliospheric Observatory (SOHO). By marking faint, fast-moving objects in real spacecraft images, citizen scientists have already helped discover hundreds of new comets—proving that even from home, you can still take part in the thrill of discovery.

But comet hunting isn’t just about being first—it’s about the wonder of watching these dynamic objects change from night to night. Even if you never discover one, there’s real joy in following a comet’s progress across the sky, noting its changing brightness or evolving tail through binoculars or a telescope. Each comet tells a story millions of years in the making, and observing them connects you to the long lineage of skywatchers who’ve done the same.

For those who enjoy structured observing challenges, the Astronomical League’s Comet Observing Program offers a fun and rewarding way to explore comets in more detail. Participants observe and record comets’ positions, brightness, and appearances over time—learning how to identify them and appreciate their subtle variations. Completing the program earns you a certificate and pin, but more importantly, it deepens your understanding of these fascinating remnants of the early solar system.

Whether you’re tracking a bright visitor like NEOWISE in the night sky or combing through spacecraft data online, comets remain one of the most exciting and accessible frontiers for amateur astronomers.

Keep Looking Up

Whether they’re found by a backyard astronomer or a billion-dollar spacecraft, comets remind us that our solar system is still full of surprises. Each new discovery connects us to the deep past—and invites us to keep watching the skies.

Clear skies and happy comet-hunting!