Comets: What They Are and How to Photograph Them

Comets are among the most dramatic objects you can see or photograph in the night sky — icy wanderers that grow glowing heads and sweeping tails as they fall toward the Sun. I have been photographing them since 2008, and few targets reward patience the way a bright comet does. This guide explains what a comet actually is, where comets come from, the difference between short- and long-period comets, the famous ones worth knowing in 2026, and a hands-on workflow for observing and photographing them yourself.

What is a comet?

A comet is a small icy body — often called a “dirty snowball” — that orbits the Sun on a long, stretched path. So what is a comet made of? At its core sits a nucleus of frozen water, carbon dioxide, ammonia and methane, mixed with dust and rocky grains. For most of its orbit the comet is dark, cold and invisible, often only a few kilometers across.

Everything changes as a comet approaches the Sun. Solar heat causes the frozen ices to sublimate — turning directly from solid to gas — which releases dust and forms the spectacular features we see from Earth. Without that heating, a comet is just a frozen lump drifting in the dark.

For context on how comets fit alongside the other worlds in our neighborhood, see our overview of the solar system and how it compares with the major planets.

What are the parts of a comet?

The parts of a comet are the nucleus, the coma, and the tails — the dust tail and the ion tail. Each becomes visible only when the comet is active near the Sun. Understanding these parts is the key to both observing and photographing comets well.

The nucleus

The nucleus is the solid heart of the comet: a porous mix of ice, dust and rock, typically between 1 and 50 kilometers wide. It is extremely dark, reflecting only a few percent of sunlight — darker than fresh asphalt. The nucleus is the source of all the gas and dust that creates the rest of the comet’s anatomy.

The coma

As ices vaporize, they form a vast, roughly spherical cloud of gas and dust around the nucleus called the coma. The coma can swell to hundreds of thousands of kilometers across — larger than many planets. When you look at a comet through a telescope, the fuzzy glowing head you see is the coma, not the tiny nucleus hidden inside it.

The dust tail and the ion tail

A bright comet usually shows two distinct tails. The dust tail is made of fine particles pushed gently away by sunlight (radiation pressure); it appears yellowish-white and often curves along the comet’s orbital path. The ion tail (or gas tail) forms when ultraviolet light strips electrons from gas molecules, and the solar wind blows these charged particles straight away from the Sun. The comet tail structure is one reason every tail always points away from the Sun — not behind the comet’s direction of travel, as many people assume. That means a comet can appear to travel tail-first as it heads back out into the solar system.

Where do comets come from?

Comets come from two cold reservoirs at the outer edges of the solar system: the Kuiper Belt and the Oort Cloud. Both are leftover material from the formation of the planets some 4.6 billion years ago, preserved in the deep freeze of deep space.

The Kuiper Belt

The Kuiper Belt is a doughnut-shaped region beyond Neptune, stretching roughly from 30 to 50 astronomical units (AU) from the Sun. It is home to icy bodies including Pluto and many trans-Neptunian objects. Gravitational nudges occasionally send a Kuiper Belt object inward, where it becomes a relatively short-period comet. NASA describes the belt as a vast disc of icy remnants from the solar system’s birth (NASA Science — Comets).

The Oort Cloud

The Oort Cloud is a vast spherical shell of icy bodies thought to surround the solar system at distances of up to 100,000 AU — nearly a quarter of the way to the nearest star. It is the source of long-period comets. A passing star or galactic tide can dislodge an object from the Oort Cloud, sending it on a journey of thousands or even millions of years toward the inner solar system. The Oort Cloud has never been directly observed; its existence is inferred from the orbits of the long-period comets that arrive from every direction in the sky.

What is the difference between short-period and long-period comets?

The difference is orbital period: short-period comets complete an orbit in under 200 years, while long-period comets take longer — sometimes millions of years. This single number tells you where a comet came from and how often you can hope to see it again.

Short-period comets

Short-period comets mostly originate in the Kuiper Belt and have relatively flat, predictable orbits aligned with the plane of the planets. Halley’s Comet, with its 76-year orbit, is the most famous example. Because they return on human timescales, short-period comets can be observed and modeled across multiple apparitions, which makes their behavior far easier to forecast.

Long-period comets

Long-period comets fall in from the Oort Cloud on enormous, often nearly parabolic orbits that can be tilted at any angle. Many are seen only once in recorded history. These are frequently the brightest and most spectacular comets — but also the least predictable, since a fresh, ice-rich nucleus can flare unexpectedly or, just as easily, fizzle and crumble as it nears the Sun.

What are the most famous comets?

The most famous comets include Halley, Hale-Bopp, NEOWISE and Tsuchinshan-ATLAS — each a milestone for skywatchers. Below is a quick reference for the headline comets of the modern era.

Halley — the comet that started it all

Halley’s Comet is the only naked-eye comet that can return within a single human lifetime. Edmond Halley predicted its return in 1758, proving comets orbit the Sun. It last graced our skies in 1986 and reached aphelion — its farthest point at 35 AU — on 9 December 2023, meaning it is now slowly falling back toward us. Its next perihelion is forecast for 28 July 2061, and that apparition should be far brighter than 1986 (Halley’s Comet — Wikipedia). Halley is also the parent of two annual meteor showers, the Eta Aquariids and the Orionids.

Hale-Bopp and NEOWISE

Hale-Bopp dominated the sky for a record-breaking 18 months in 1996–97 and is the benchmark “Great Comet” for a whole generation. NEOWISE, in July 2020, was the brightest comet visible from the Northern Hemisphere in decades and became a global phenomenon during the pandemic summer — the comet that pulled countless people into astrophotography.

Tsuchinshan-ATLAS — the standout of recent years

Comet C/2023 A3 (Tsuchinshan-ATLAS) made its closest approach to Earth on 13 October 2024 at about 0.47 AU and peaked near magnitude −4.9 around 9 October — the brightest comet seen from the Northern Hemisphere since Hale-Bopp in 1997, with a tail stretching roughly 21 degrees across the sky. I imaged it from the Southern Hemisphere as it emerged at dawn, and it is the finest comet I have photographed in my remote-rig era.

How do you observe comets with the naked eye and binoculars?

To observe a comet, find a dark site away from light pollution, check its position for your date, and start with binoculars before reaching for a telescope. Most comets are diffuse, low-contrast objects, so dark skies matter more than aperture.

• Use a finder app or ephemeris to know exactly where and when the comet rises — many are best at dawn or dusk, low to the horizon.
• Start with 10×50 binoculars. Their wide field shows the coma and tail far better than a high-power telescope, which over-magnifies and dims the view.
• Let your eyes dark-adapt for 20–30 minutes and use averted vision — looking slightly to the side — to catch faint tail structure.
• Time it right. A comet is usually best within a week or two of perihelion or its closest approach to Earth.

How do you photograph comets?

To photograph a comet, use a tracking mount, shoot many short exposures, and stack them aligned on the comet’s nucleus rather than the stars. How to photograph comets well comes down to matching your gear and exposure to how fast the comet is moving against the background stars. Here is the workflow I use on my remote rig at Deepsky Chile (an Alluna 12.5″ RC on a Paramount MX+), adapted for portable setups too.

Choosing your gear: wide-field versus telescope

For a big, bright comet with a long tail — like NEOWISE or Tsuchinshan-ATLAS — a DSLR or mirrorless camera with a 50–200mm lens on a small star tracker captures the whole tail and the landscape context. A telescope is the wrong tool here: its narrow field crops the tail. Reserve the telescope for fainter, more compact comets where you want detail in the coma and inner tail. Before a session I plan framing with our telescope field of view calculator to confirm the tail will fit the sensor.

Camera settings and exposure

Comets move noticeably against the stars, so individual exposures must be short enough to keep the nucleus sharp. Start near these values and adjust:

• Wide-field lens: ISO 1600–3200, aperture f/2.8–f/4, 8–30 second subs on a tracker.
• Telescope: 30–120 second subs depending on the comet’s apparent motion; faster comets demand shorter subs.
• Shoot RAW, take dark and flat calibration frames, and gather as many subs as the comet’s altitude allows.

To dial in exposure time for your sky brightness and optics, our astrophotography calculator takes the guesswork out of sub-exposure length.

Stacking on the comet nucleus

This is the step that separates a smeared snapshot from a clean comet image. Because the comet drifts relative to the stars, normal star-aligned stacking blurs the comet, while comet-aligned stacking blurs the stars. The professional approach is to stack twice: once aligned on the stars and once aligned on the comet nucleus, then blend the two so both render sharp. Software such as PixInsight, DeepSkyStacker and Siril all offer dedicated comet-stacking modes — tell the program to register on the nucleus, and it compensates for the comet’s motion frame by frame.

Practical field tips from experience

• Polar-align carefully even for short subs — field rotation ruins the corners over a long sequence.
• Capture early. Comets near the horizon set or rise fast; you often have a 30–45 minute window in dark sky.
• Don’t over-stretch. The faint ion tail lives in the shadows; lift it gently to avoid amplifying noise and gradients.
• Mind the Moon. Plan around a dark Moon phase — moonlight washes out the delicate tail more than it does stars.

Are comets dangerous, and what can we learn from them?

Comets are not an everyday danger, but they are scientifically priceless. Impacts are rare on human timescales, and astronomers track near-Earth objects — including comets and asteroids — to give years of warning. Far more valuable is what comets teach us: as nearly unchanged relics from the birth of the solar system, they carry pristine ices and organic molecules. The ESA Rosetta mission, which orbited comet 67P/Churyumov-Gerasimenko and landed the Philae probe in 2014, found that comets likely helped deliver the raw ingredients for water and organic chemistry to the early Earth (ESA — Rosetta mission).

Frequently asked questions

What exactly is a comet made of?

A comet is made of frozen ices — mainly water, carbon dioxide, ammonia and methane — mixed with dust and rocky grains, which is why it is nicknamed a “dirty snowball.” Its solid core, the nucleus, stays frozen until it nears the Sun, when heat vaporizes the ices to form the glowing coma and tails.

Why does a comet’s tail always point away from the Sun?

Because the tail is shaped by solar radiation pressure and the solar wind, both of which flow outward from the Sun. They push the comet’s dust and ionized gas directly away from the Sun regardless of which way the comet is moving. On its outbound journey, a comet therefore appears to travel tail-first.

When will Halley’s Comet be visible again?

Halley’s Comet will next reach perihelion on 28 July 2061. It passed its farthest point from the Sun in December 2023 and is now slowly returning inward. The 2061 apparition is expected to be considerably brighter than its faint 1986 showing because the comet will be on the same side of the Sun as Earth.

What is the best comet to have appeared recently?

Comet C/2023 A3 (Tsuchinshan-ATLAS) in October 2024 was the standout, peaking near magnitude −4.9 — the brightest comet visible from the Northern Hemisphere since Hale-Bopp in 1997, with a tail about 21 degrees long. Before that, NEOWISE in July 2020 was the brightest in decades.

How do I photograph a comet without star trailing?

Use a tracking mount and keep individual exposures short — roughly 8–30 seconds with a wide lens, or 30–120 seconds through a telescope depending on how fast the comet moves. Then stack your frames twice, once aligned on the stars and once on the comet nucleus, and blend the results so both stars and comet stay sharp.

Written by Hamza Touhami, astrophotographer since 2008, imaging from a remote rig (Alluna 12.5″ RC on a Paramount MX+) at Deepsky Chile.