What Is a Comet? | NASA Space Place – NASA Science for Kids
Why do comets have such eccentric orbits? | Astronomy.com
Comets: Everything you need to know | Space
Halley's Comet - Wikipedia
Why Comets Are Important - NASA Solar System Exploration
The Comet's Tale: Orbits - University of California, Berkeley
Halley's Comet begins its 38-year journey back toward Earth tonight
1P/Halley - NASA Science
NASA Researchers Discover More Dark Comets
Hubble Confirms Largest Comet Nucleus Ever Seen - Science@NASA