NYTimes writer Shannon Hall on “How to Watch the ‘Green Comet’ in Night Skies”:
Comets are clumps of dust and frozen gases, sometimes described by astronomers as “dirty snowballs.” Most are believed to originate from the distant, icy reaches of the solar system where gravitational agitations sometimes push them toward the sun — an interaction that transforms them into gorgeous cosmic objects.
When they leave their deep freeze, the heat from the sun erodes their surfaces, and they start spewing gases and dust until they host a glowing core, known as the coma, and a flamelike tail that can stretch for millions of miles.
“They’re alive,” Laurence O’Rourke, an astronomer with the European Space Agency, said. “When they’re far from the sun, they’re sleeping, and when they get close to the sun, they wake up.”
Emphasis mine. (Thanks to Meg for this.)
Filed under: astronomy