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Comet Catalina Coming To a Night Sky Near You (www.cbc.ca)
TigerNut writes: CBC is running a story on the upcoming closest approach of Comet Catalina. While the headline makes it sound like a one-night deal for the morning of January 1, the best viewing may actually occur next weekend (Jan 8-10) because the moon will not be a bright distraction at that time. The CBC reports: "Comet Catalina, which is less than 20 kilometres across, was discovered in 2013 by the Tuscon, Ariz.-based Catalina Sky Survey, which looks for potentially hazardous near-Earth objects. At first, it was thought to be a very large near-Earth asteroid. But astronomers soon realized it was actually a very long, near-parabolic orbit and observations with the Canada-France-Hawaii telescope showed 'modest cometary activity.'"
What the hell does that mean?
If it's parabolic but really really long, "near-hyperbolic" would be a reasonable description -- that's not out of the ordinary for comets.
Presumably it means that its orbit is closed - elliptical - but is only very loosely gravitationally bound--perhaps even more so that most comets. In other words, its velocity is only just shy of escape velocity, hence near-parabolic. Yes, mathematically speaking, that means that its orbit must also be near-hyperbolic; an infinitesimal increase in velocity converts a parabolic path into a hyperbolic one (and an infinitesimal decrease in velocity converts a parabolic path into a long-period ellipse).
~Idarubicin