What Is A Comet?
A comet is a celestial object that is composed mainly of dust, rocks, water ice, and frozen gases. They are often referred to as ‘dirty snowballs‘ because of their composition, made of material left over from the formation of our solar system.
They are relatively small objects with highly elliptical orbits, spending most of their time in the distant reaches of our solar system.
It can take hundreds, even thousands of years for these objects to complete their orbit. But they do venture into the inner parts of our solar system as they approach the Sun.
Comets can vary in brightness, as their comas and tails reflect sunlight or glow due to absorbed energy. Some are bright enough to be visible to the naked eye, while others are faint and require a telescope for observation.
Characteristics of a Comet
Each one processes the same characteristics:
- Nucleus: at the core is the nucleus, which is a mixture of water ice, frozen gases, dust, and rock. It is a few kilometers in diameter and is considered the central part of the comet.
- Tails: each one has two types of tails because the gas and dust are influenced by sunlight in different ways. A dust tail, which is composed of small dust particles, and an ion tail, which is made of charged particles. Both tails point away from the Sun and get longer as the comet approaches the Sun.
- Coma: heat causes the solid ice within the nucleus to turn into gas through sublimation when it approaches the Sun. This creates a hazy/glowing type cloud around the nucleus, known as the coma. Along with the tail, this is what gives a comet its distinctive appearance.
A comet is a small, icy body that orbits the Sun and releases gas and dust when heated. Each comet has a frozen nucleus (ice, rock, organic material), a glowing coma that forms as it nears the Sun, and often two tails (a gas tail and a dust tail) that always point away from the Sun.
A glowing ion tail is evident in my photo of Comet C/2025 A6 Lemmon in 2025.
Where Do Comets Come From?
They are considered some of the most primitive and ancient objects in the solar system, dating back 4.6 million years.
According to NASA, Gerard Kuiper theorized that a belt of ice particles existed beyond Neptune. It is here where icy objects are sometimes nudged into orbit via gravity, bringing them closer to the Sun.
These are considered short-period comets, taking less than 200 years to complete their orbit around the Sun. In some cases, these comets could even be predicted by scientists based on their previous appearances.
There are also long-period comets that arrive from a farther region referred to as the Oort Cloud. This region is so far away that it can take comets from this region 30 million years to complete their orbit around the Sun.
Comet Tempel 1 Impact. NASA/JPL-Caltech/UMD.
“This spectacular image of comet Tempel 1 was taken 67 seconds after it obliterated Deep Impact’s impactor spacecraft.” NASA Solar System Navigation.
Comet 3I/ATLAS: A Comet From Outside Our Solar System
Discovered on July 1, 2025, by the Asteroid Terrestrial‑impact Last Alert System (ATLAS) survey telescope in Chile, 3I/ATLAS is an interstellar comet, the third such object ever confirmed to pass through our solar system.
Astronomers estimate it may be more than 7 billion years old, predating the formation of the Sun, which suggests it formed around a distant star in the Milky Way.
As it hurtles toward perihelion (its closest approach to the Sun) at roughly 1.36 AU (between the orbits of Earth and Mars), 3I/ATLAS is already showing a growing coma and tail, providing a rare opportunity to study material from another star system.
Although it poses no threat to Earth, its hyperbolic trajectory and composition make it a key target for astrophotographers and scientists alike.
When Are Comets Visible?
As mentioned, these objects spend most of their time in the outer part of the solar system in the Oort Cloud or Kuiper Belt, only coming close to the Sun every few thousand or million years.
They are most easily visible when they get close to the Sun, and the ice particles on the surface turn into gas. This creates a cloud of gas and dust around the comet’s nucleus, making it much easier to see.
The tail will grow as the comet gets warmer, potentially reaching millions of kilometers in length, making it easier to see.
Chart showing the location of Comet C/2023 A3 Tsuchinshan-ATLAS. Sky at Night Magazine.
A detailed star chart or comet finder map is essential for anyone wanting to locate and track a comet in the night sky. By marking the comet’s path among the stars, these charts help visual observers know exactly where to find the comet on any given night. For astrophotography, a chart of the comet’s trajectory lets you plan your framing, anticipate close passes with bright stars or deep-sky objects, and capture the comet’s changing position with precision.
Why Do Comets Have Tails?
Comets have tails because they are made of ice, dust, and frozen gases that begin to heat up as they travel closer to the Sun. This process, known as sublimation, causes the solid ice in a comet’s nucleus to vaporize, releasing gas and dust into space.
The Sun’s heat and solar wind push this material outward, forming the comet’s distinctive tail. This is the most recognizable feature of a comet, which sets it apart from asteroids and meteoroids.
A comet actually develops two separate tails: a bright dust tail and a faint ion (gas) tail. The dust tail reflects sunlight and often appears curved, while the ion tail glows with a bluish hue as charged particles interact with the solar wind. Both tails always point away from the Sun, regardless of the comet’s direction of travel.
Observing a comet’s tail gives scientists valuable insight into its composition and the dynamic forces shaping our solar neighborhood. The first comet I ever photographed was Comet NEOWISE in 2020, and I was amazed to see such a bright, extended tail in my images.
Comet NEOWISE captured from my backyard in 2020.
Difference Between Comets and Asteroids
They are both planetary objects that formed in the early history of our solar system and orbit the Sun. However, the main difference between the two is their composition.
An asteroid is typically found in the asteroid belt between Mars and Jupiter. They are small, rocky objects that can be found in a variety of different shapes and sizes.
This is different from a comet, which is made of ice and dust that vaporizes as it gets closer to the Sun.
Comets can also leave a trail of debris behind them that can lead to meteor showers on Earth. For instance, the Perseid meteor shower occurs every year between August 9 and 13 when Earth passes through the orbit of Comet Swift-Tuttle.
Interstellar visitor `Oumuamua’ racing toward the outskirts of our solar system. NASA, ESA, and J. Olmsted and F. Summers (STScI).
Famous Comets
Comets are named after the people who discovered them, and include other details such as the type of orbit and year of discovery. Here are some of the more famous ones:
- Comet Halley: perhaps the most famous, it was named after Sir Edmund Halley, who predicted it would return. Its sightings and history have been well documented, and it returns to the inner solar system roughly every 76 years.
- Comet Shoemaker-Levy 9: famous for its collision with Jupiter in 1994. It broke apart into fragments, which impacted Jupiter over several days. It provided valuable insights into the dynamics of comets.
- Comet Hale-Bopp: one of the most widely observed comets in the 20th century. It was visible for 18 months from 2995 – 1997 and could be seen with the naked eye, generating significant public interest.
- Comet NEOWISE: discovered by a NASA space telescope, it was visible in July 2020. Many people were interested in seeing and photographing the comet, and it was a beautiful sight in the night sky.
- Comet Lemmon (C/2025 A6): Comet Lemmon is a non-periodic comet discovered on January 3, 2025. The comet became unexpectedly bright, making it an interesting target for observers in late 2025.
These events have left their mark on astronomy and the general public’s awareness due to their impressive appearances.
My experience photographing Comet NEOWISE in 2020. (AstroBackyard/YouTube).
Tips for Photographing a Comet
Some of the most recent comets highlighted in the media include C/2022 E3 ZTF (2023) and Neowise (2020). Many people were eager to see and even photograph these objects.
One of the easiest ways to successfully capture your first comet photo is to use a beginner-friendly smart telescope. These devices make it much easier to locate and focus on the comet.
My best comet photos were taken with an astrophotography telescope and a dedicated astronomy camera. For example, my image of Comet Lemmon used 40 x 60-second tracked exposures through a small refractor telescope.
If you are preparing to photograph a comet, there are a few things you’ll want to keep in mind:
- Decide on your composition: You can track the comet itself with a star-trail background or capture the motion of the stars, and the comet will be blurred. Unlike a typical deep-sky object, they are moving independently from one another.
- Tracking: For the ultimate portrait, you’ll definitely want your telescope to track the COMET – this will allow you to take a clear, long-exposure shot. You may want to stick to shorter subs, tracking the stars, and stacking the image.
- Use the correct stacking mode: The stacking process is a bit different for comets. There are comet-stacking modes in both DeepSkyStacker and PixInsight. Try both to see which one delivers the best result.
- Get Creative: Many people like to create an animated timelapse of the comet traveling through the stars. This is an interesting effect because you can see how fast it’s actually moving through space.
The “Green Comet “from 2023, formally known as C/2022 E3 ZTF.
Get a more detailed breakdown of how I photographed Comet C/2022 E3 ZTF.