Most comets are only visible through telescopes. Why do some become spectacular naked-eye sights?
Most comets are only visible through telescopes. Only a few times per decade does a comet become bright enough to be an easy naked-eye sight, like comet NEOWISE in July 2020.
Three factors
- Size and activity: a larger nucleus with more ice releases more gas and dust.
- Distance from the Sun: the closer a comet gets to the Sun, the more ice evaporates.
- Distance from Earth: a comet that passes close to Earth looks brighter.
Hard to predict
Comet brightness is notoriously hard to predict. Some comets that promised to be spectacular broke apart or fizzled out, while others brightened unexpectedly. As comet hunter David Levy once said, comets are like cats: they have tails, and they do precisely what they want.
Image: Comet NEOWISE Over Washington. Credit: NASA/Bill Ingalls. Source, NASA media guidelines.
Comments
As my username suggests, this is my favourite topic. NEOWISE was the best sky show I have ever seen.
Love the cat quote!
Is there a bright comet expected in the coming years?
In reply to by nebula_ivo
Nobody knows. Many bright comets are discovered only months before they reach their best. Keep watching the news.
The dust tail and the gas tail point in slightly different directions, which is easy to see in good photos.