View Full Version : Can a comet be naked-eye visible for an entire year?
2010-Sep-25, 05:04 PM
I came across the following eye-witness report from 536 AD:
"a star which certain call a comet, with a ray like a sword, appeared over that country through a whole year, and the sky seemed to be on fire and many other signs were seen."
Under what conditions would it be possible for a comet to be visible to a naked eye observer for an entire year?
2010-Sep-25, 06:39 PM
According to Wiki, the Great Comet of 1811 was visible to the naked eye for almost 9 months, and Hale-Bopp for twice that. They seem to have two things in common:
*They were both unusually--and intrinsically--large and bright.
*Both have fairly distant perihelia, about 1 AU for both. This means they traveled slower at perihelion relative to the Earth than one with a much tighter orbit (compare to 1965's Ikeya-Seki, which was extremely bright but not visible for very long), which probably also extended the window of their visibility.
2010-Sep-28, 10:14 PM
Now, what I wanted to see was something twice as big as Hale Bopp half as close as Hyakutake. THAT would be my idea of a great Comet
2010-Sep-29, 05:01 AM
What Romanus said. Basically if their closet orbit was about the same radius as the Earth's orbit and if they where large enough then they would be visible for a very long time. IE on its trip in we'd see it from fairly far out and as it passes around the sun so would we keeping it in view, from some spot on Earth, then on its way out we'd still see it. The larger the comet the brighter it would appear for longer and if typical make up would also have a significant tail. Also such a long viewing time would be indicative of a comet that has a very long orbital period.
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