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A chunk of ice and rock that orbits a star. In our solar system, the majority of comets orbit well beyond Pluto, in regions known as the Kuiper Belt and the Oort Cloud. Most comets are no more than a few miles in diameter. Upon close encounters with the Sun, comet ices vaporize, creating a coma, or cloud, around the comet, and a long tail that always points away from the Sun.


Craters and Extinctions February 19, 2016


Comets February 19, 2016

Radio Programs

Perseid Meteors Fireworks big and small from a comet August 11, 2021

Nicholas Bobrovnikoff A comet sparks a career in astronomy April 29, 2021

Lyrid Meteors Reminders of an infrequent visitor April 20, 2021

Comet Hyakutake A flash visitor pays a brief call March 24, 2021

Orionid Meteors The calling cards of a distant comet October 20, 2020

Comet NeoWise A bright comet in the evening sky July 21, 2020

Oort Cloud Notes from the edge of the solar system June 22, 2020

Lexell’s Comet A really close encounter with a comet June 14, 2020

Double Showers One night, two meteor showers April 21, 2020

Lewis Swift From merchant to cosmic celebrity February 28, 2020

Cometary Water Splashing cool water on a hot debate November 6, 2019

Fear and Loathing Great fear over great beauty November 5, 2019

Discovering Comets Discovering balls of rock and ice November 4, 2019

Comets Solar system studies in contrast November 3, 2019

Moon and Jupiter Blasting a giant planet July 13, 2019

Comet Wirtanen A special visitor for the bull December 13, 2018

Comet Wirtanen A hyperactive comet gets close November 28, 2018

Comet Tails Making a comet a comet November 27, 2018

The ‘Angry Star’ Words about an “angry star” November 18, 2018

Leonid Meteors A quiet but steady meteor shower November 16, 2018

Draconid Meteors Sparks or misfires from the dragon? October 8, 2018

Catching Dust Catching dust in the stratosphere June 19, 2018

Great Comet A comet that overperformed February 5, 2018

Orionid Meteor Shower Sparks from a distant comet October 20, 2017

Encke’s Comet A faint comet in the evening sky February 16, 2017

End of Rosetta Final rendezvous with a comet September 5, 2016

Perseid Meteors Finding the cause of meteor showers August 10, 2016

Moon and Jupiter Vacuuming up some trouble August 5, 2016

Close Visitor Keeping an eye on a close visitor March 12, 2016

Assault on a Comet A fleet takes aim at a comet March 5, 2016

Doomed Comets Tracking doomed comets — after this. January 20, 2016

Stardust Catching bits of stardust January 15, 2016

Featured Images

Diagram of the orbit of 2014 UN271, a giant comet in the outer solar system

Big Visitor June 23, 2021

Comet Hyakutake, March 25, 1996

Brilliant Visitor March 24, 2021

Wide-angle and close-up views of Comet NeoWISE

Cometary Close-Up August 24, 2020

A triple comet near the Sun

Seeing Triple August 14, 2020

Comet Neowise at Dawn

Dawn Visitor July 9, 2020

Comet NeoWISE in the dawn sky, July 5-9

Dawn Comet July 3, 2020

Hubble Space Telescope image of Comet Atlas

Breaking Up May 2, 2020

Shoemaker-Levy 9 takes aim at Jupiter

Taking Aim July 13, 2019

1910 promotional illustration for comet pills

A Bill of Goods April 19, 2019

Comet Wirtanen's path across the December sky

Passing the Bull December 9, 2018

Space-dust collecting aircraft

Dust Collector June 19, 2018

Great Comet of 1843

Great Comet February 5, 2018

The most distant active comet yet seen

Distant Snowball October 3, 2017

Encke's Comet in mid-February

Evening Comet February 16, 2017

A comet in the February pre-dawn sky

Green Visitor February 8, 2017

Artist's concept of 2016 WF9

Heading In January 1, 2017

SOHO view of a Kreutz Sun-grazing comet

Racing Toward Its Doom August 3, 2016

Giotto view of Halley's Comet, March 1986

Assault on a Comet March 5, 2016

View of a doomed comet approaching the Sun

Doomed Comet January 20, 2016

Comet ISON has disintegrated

Comet Fizzles? September 14, 2015

Comet ISON streaks ever-closer to the Sun in this November 19 image

Breaking Up? September 14, 2015

Comet Crawl September 14, 2015

Images of Comet Churyumov-Gerasimenko on August 12

Busy Comet August 15, 2015

Rosetta view of Comet Churyumov-Gerasimenko on March 22, 2015

Messy Comet April 2, 2015

Rosetta view of Comet Churyumov-Gerasimenko on February 14, 2015

Imhotep February 21, 2015