Comet names can look cryptic, but they follow a structured system used by astronomers to identify when a comet was found, how it moves, and who discovered it.
Understanding that system makes it much easier to read comet alerts, catalog entries, and skywatching reports.
How do comet names work?
Comet names work by combining a discovery year, a letter code for the discovery date, and a number that shows the order of discovery in that period.
In many cases, the name also includes the discoverer’s name or an observatory label, and periodic comets receive an additional catalog number such as 1P or 67P.
Unlike star names, comet designations are not meant to be poetic.
They are functional labels created by the International Astronomical Union (IAU) and used by the Minor Planet Center and other astronomical catalogs to keep track of objects that may appear briefly, split apart, or return on long cycles.
The basic parts of a comet designation
A modern comet designation often contains several elements, each with a specific meaning.
The format is designed to answer three questions at a glance: when was it discovered, what kind of comet is it, and which comet is it among others found in that same interval?
- Discovery year: the year the comet was found.
- Letter code: the half-month of discovery.
- Discovery order: the number of the comet discovered in that half-month.
- Type prefix: a code such as C/, P/, D/, X/, or A/.
- Discoverer name: the person, survey, telescope, or observatory that found it.
For example, a designation like C/2023 A3 (Tsuchinshan–ATLAS) tells you the comet was discovered in 2023, during the first half of January, and was the third comet reported in that time period.
The name in parentheses identifies the discovery sources.
What the prefix letters mean
The first character in a comet designation is especially important because it describes the comet’s orbital status or classification.
C/ for non-periodic comets
C/ is used for comets that are not known to return within about 200 years.
These may be long-period comets from the Oort Cloud or new visitors making a first recorded trip through the inner solar system.
Many famous bright comets, including spectacular naked-eye objects, fall into this category.
P/ for periodic comets
P/ identifies periodic comets with confirmed return visits.
These comets have orbits that bring them back on predictable timescales, usually less than 200 years.
One of the best-known examples is 1P/Halley, which returns roughly every 76 years.
D/ for destroyed or lost comets
D/ is used for comets that have been lost or have broken apart.
Some were observed once and never found again, while others disintegrated after passing close to the Sun or encountering gravitational disruption.
X/ for comets with uncertain orbits
X/ is reserved for comets with poor orbital data.
This usually means astronomers do not have enough observations to determine a reliable path through the solar system.
A/ for objects first thought to be comets
A/ is used when an object was initially reported as a comet but later determined to be an asteroid or another non-cometary body.
This helps preserve the historical record without implying a false classification.
How the letter-number code is assigned
The letter-number portion follows a system that groups discoveries into half-month periods.
The letters run through the year in sequence, skipping the letter I to avoid confusion with the number 1.
- A = January 1–15
- B = January 16–31
- C = February 1–15
- D = February 16–28/29
- …
- Y = December 16–31
The number after the letter shows the order of discovery within that half-month.
So 2024 G2 means the second comet discovered in the first half of April 2024, since G corresponds to April 1–15.
This system is especially useful because comets are often discovered in large survey programs such as ATLAS, Pan-STARRS, and the Zwicky Transient Facility, which may report several new objects in a short time.
Why some comets also have names in parentheses
After the official designation, a comet often includes a discoverer credit or the name of the survey that found it.
This can be a person, an observatory, or a mission.
- Hale-Bopp: named for independent discoverers Alan Hale and Thomas Bopp.
- Tsuchinshan–ATLAS: linked to Chinese observatory reports and the ATLAS survey.
- NEOWISE: discovered by NASA’s NEOWISE infrared space telescope.
In practice, the discoverer name is partly historical and partly informational.
It reflects who first reported the object, but the official astronomical designation remains the standardized label used in catalogs and research papers.
What periodic comet numbers like 1P or 67P mean
Periodic comets receive a sequential number before the prefix P/ once their orbits are well established.
The number is not related to brightness, size, or age.
It simply marks the order in which the comet was confirmed as periodic.
- 1P/Halley is the first recognized periodic comet.
- 2P/Encke is the second.
- 67P/Churyumov-Gerasimenko is the 67th periodic comet cataloged.
These numbers remain stable even if the comet is later studied by spacecraft or reclassified in other ways.
That stability is one reason the system is so important for scientific communication.
How comets get provisional and permanent names
When a comet is first spotted, it usually receives a provisional designation.
Astronomers then follow it over days or weeks to measure its orbit.
If enough observations confirm its nature, the designation is finalized under IAU rules.
A comet may initially be labeled with a survey code or temporary report name before the more complete format is issued.
This staged process helps astronomers avoid duplicate reports and distinguish real comets from asteroids, noise in imaging data, or transient artifacts.
If later observations show the object is actually an asteroid, the designation can change from a comet-style label to an asteroid classification.
That is one reason comet naming can seem fluid during the early stages of discovery.
Common examples of comet naming in practice
Seeing examples is often the fastest way to understand the system.
- C/2020 F3 (NEOWISE): a non-periodic comet discovered in the first half of March 2020.
- 67P/Churyumov-Gerasimenko: a periodic comet and target of the ESA Rosetta mission.
- C/1995 O1 (Hale-Bopp): one of the most famous bright comets of the late 20th century.
- 1P/Halley: the iconic periodic comet visible from Earth on a roughly 76-year cycle.
Each example shows how the prefix, year, half-month code, and discoverer information combine to create a compact scientific label.
Why comet naming matters for astronomy and skywatching
Comet names do more than identify objects.
They help astronomers compare observations across centuries, determine orbital evolution, and communicate about potential hazards or observing opportunities.
For skywatchers, they make it easier to follow news about upcoming comets and distinguish one object from another.
Because many comets are discovered by automated surveys, the naming system also preserves credit and traceability.
A label can link an object to a telescope network, a specific observing campaign, or the first amateur report that caught attention.
How to read a comet name quickly
If you want a fast way to decode a comet designation, use this checklist:
- Look at the prefix to identify whether it is periodic, non-periodic, lost, uncertain, or misclassified.
- Check the year to see when it was discovered.
- Translate the letter code to the half-month of discovery.
- Read the number to determine the discovery order within that period.
- Note the parenthetical name for the discoverer, observatory, or survey.
Once you know the pattern, comet names become efficient scientific shorthand rather than confusing strings of letters and numbers.
They reveal both the object’s discovery history and its place in the broader catalog of solar system bodies.