Space & Beyond • Strange Sky Events • Cosmic Visitors
Comets are icy cosmic bodies that brighten dramatically as they approach the Sun, sometimes growing enormous glowing tails visible across Earth’s skies. Throughout history, comets have terrified civilizations, inspired myths, triggered apocalyptic fears and fascinated astronomers.
This Strange Sounds pillar explains how comets form, why they develop tails, why some appear green, how sungrazers survive close solar encounters, why comets fragment or explode, and how famous objects like Halley’s Comet and NEOWISE became some of the most spectacular sky events ever observed.
This page also explores comet visibility, comet-caused meteor showers, long-period visitors from the Oort Cloud, and the difference between comets, asteroids, meteors and atmospheric fireballs.
TL;DR
- Comets are icy bodies orbiting the Sun.
- Comet tails form when solar radiation heats frozen material.
- Some comets appear green because of glowing carbon molecules.
- Sungrazers pass extremely close to the Sun.
- Comets can fragment or explode during solar heating.
- Meteor showers often originate from comet debris streams.
- Halley’s Comet is the most famous recurring comet in history.
- Long-period comets may originate from the distant Oort Cloud.
What is a comet?
A comet is an icy Solar System body composed of frozen gases, dust, rock and organic material.
Unlike asteroids, which are primarily rocky or metallic, comets contain volatile ices that vaporize when approaching the Sun.
The main parts of a comet include:
| Comet Structure | Description |
|---|---|
| Nucleus | Solid icy core containing rock, dust and frozen gases. |
| Coma | Cloud of gas and dust surrounding the nucleus. |
| Dust Tail | Sunlit particles pushed away by solar radiation. |
| Ion Tail | Electrically charged gas interacting with solar wind. |
Many comets originate from:
- The Kuiper Belt
- The distant Oort Cloud
Why comets have tails
Comet tails form when solar heat vaporizes ice inside the comet nucleus.
As frozen gases escape into space, they drag dust outward and interact with solar radiation and solar wind.
Comets usually develop two main tails:
- Dust tail
- Ion tail
The ion tail often glows blue because of ionized gases interacting with solar wind.
Importantly:
Why some comets appear green
Some comets develop a bright green glow caused by diatomic carbon molecules.
As ultraviolet sunlight breaks apart comet gases, certain carbon compounds emit green light.
This effect became famous during appearances of:
- C/2022 E3 (ZTF)
- Comet Lovejoy
- Comet Leonard
Green coloration usually appears in the coma rather than the tail itself.
Famous comets in history
Historic and Famous Comets
Halley’s Comet — Recurring Every ~76 Years
- Pattern: Most famous recurring naked-eye comet
- Importance: First comet correctly predicted scientifically
- Last Appearance: 1986
- Next Return: 2061
Comet Hale-Bopp — 1997
- Pattern: Extremely bright naked-eye comet
- Visibility: Visible for record-length duration
- Importance: One of the most observed modern comets
Comet NEOWISE — 2020
- Pattern: Bright naked-eye comet during modern social-media era
- Impact: Generated worldwide photography phenomenon
- Importance: One of the brightest Northern Hemisphere comets in decades
Shoemaker-Levy 9 — 1994
- Pattern: Fragmented comet colliding with Jupiter
- Impact: Produced massive atmospheric scars on Jupiter
- Importance: First observed planetary collision in modern astronomy
Sungrazers explained
Sungrazers are comets that pass extremely close to the Sun.
Many belong to the famous:
- Kreutz sungrazer family
Some survive their close approach, while others completely vaporize or fragment.
Solar observatories like SOHO have discovered thousands of sungrazers.
Comet fragmentation and explosions
Comets are fragile objects.
As they approach the Sun, thermal stress, rotational forces and gas pressure can cause fragmentation.
Some split into multiple pieces, while others disintegrate completely.
| Fragmentation Cause | Effect |
|---|---|
| Solar heating | Surface cracking and gas explosions |
| Tidal forces | Comet breakup near planets or Sun |
| Rotational stress | Nucleus splitting |
Fragmenting comets can later produce:
- meteor showers
- debris streams
- multiple comet fragments
Comets and meteor showers
Many meteor showers occur when Earth passes through debris left behind by comets.
| Meteor Shower | Parent Comet |
|---|---|
| Perseids | Comet Swift-Tuttle |
| Orionids | Halley’s Comet |
| Leonids | Comet Tempel-Tuttle |
Explore more in: Meteor Showers Explained.
Could a comet hit Earth?
Large comet impacts are rare, but they can be catastrophic.
Long-period comets from the Oort Cloud are particularly difficult to predict because they may appear with little warning.
Potential consequences include:
- global shockwaves
- impact winters
- wildfires
- tsunamis
- mass extinctions
Explore more in: Asteroids & Near-Earth Objects Explained.
Why ancient civilizations feared comets
Throughout history, comets were often interpreted as:
- omens of war
- signs of plague
- divine warnings
- apocalyptic symbols
- heavenly messages
Ancient cultures frequently described comets as:
- hairy stars
- burning swords
- sky serpents
Their unpredictable appearances made them especially frightening before modern astronomy explained their origins.
Modern comet monitoring
Modern observatories continuously monitor comets and near-Earth objects.
Major monitoring programs include:
- NASA
- ESA
- Pan-STARRS
- SOHO
- Vera Rubin Observatory
Scientists monitor:
- brightness changes
- fragmentation
- orbital evolution
- tail development
- potential Earth approaches
Frequently Asked Questions
What is the difference between a comet and an asteroid?
Comets contain large amounts of ice and develop tails near the Sun, while asteroids are mostly rocky or metallic.
Why do some comets glow green?
Green coloration comes from glowing carbon molecules excited by sunlight.
Can comets explode?
Yes. Comets can fragment or disintegrate because of thermal stress and solar heating.
What is a sungrazer?
A sungrazer is a comet passing extremely close to the Sun.
Do comets create meteor showers?
Yes. Many meteor showers form from comet debris streams crossing Earth’s orbit.
Will Halley’s Comet return?
Yes. Halley’s Comet is expected to return in 2061.
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