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To: longshadow
Maybe we can have "wildly elliptical" as "oscillating in a straight line back and forth, e = 2.0 (defined).

Of course, not too many planets actually do that.

605 posted on 04/06/2002 5:08:26 PM PST by VadeRetro
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To: VadeRetro
Maybe we can have "wildly elliptical" as "oscillating in a straight line back and forth, e = 2.0 (defined).

Actually, we can't do that. e>=1.0 has very specific meaning; behold:


e=0 ................=> circular orbit

0 < e < 1.0 ...... => elliptical orbit

e = 1.0 ......... => parabolic trajectory

1.0 < e ......... => hyperbolic trajectory


Note that for e greater than or equal to 1.0, it isn't an orbit at all, meaning the object appears once, never to return.

The difference between a parabolic and hyperbolic trajectory is this: an object in a parabolic trajectory (which can be thought of as being on the boundary between elliptical orbits and hyperbolic trajectories) will have a velocity that approaches 0 as time approaches infinity. That is to say their kinetic energy is exactly equal to the work that must be done to overcome the graviational attraction it experiences. Objects in hyperbolic trajectories have an excess of kinetic energy, and thus their velocities will NEVER reach zero, even in an infinite amount of time. In fact, their velocities will asymptotically approach some constant value, in the limit, as time tends to infinity.

606 posted on 04/06/2002 5:29:10 PM PST by longshadow
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To: VadeRetro
Forgot to add to the preceding reply that all elliptical orbits have eccentricities lying between 0 and 1. If the eccentricity is equal or greater than 1, it isn't elliptical (in fact it isn't an "orbit"; it's a one-time trajectory).
607 posted on 04/06/2002 5:32:29 PM PST by longshadow
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