# Calculations of orbits

## Main Question or Discussion Point

Hello I have a question about calculations of orbits. Mostly my question is about Comet orbits and eccentricity and period. To help myself learn more about orbits I'm witting a simple calculator for myself so I can better grasp it. I'm getting the orbital elements from the MPC website ( I cant post the url as I need 15 posts )

for a elliptical orbit e > 0 and e < 1
While Periodic Comets e (eccentricity)
name eccentricity
17P 0.432668
26P 0.633008
180P 0.357635
P/2006 HR30 0.842973

I see alot of comets list that have a e > 0 and e < 1 and they are not listed as a periodic comet.
name eccentricity
C/2006 M4 0.999933
C/2007 E2 0.999235
C/2007 T5 0.913398

This is just a few, but shouldn't they be listed as a periodic comet also?

I understand to get the semi major axis a = q/(1 − e)
and then to get the period is $$T=\sqrt{a^3}$$

Comet C/2007 B2 Skiff
e 0.995869
q 2.974897

I get
a =720.13967562334
T = 19325.249433634 years

Does the IAU have a limit on the period time that they count a comet as periodic? I could not find it on their website.

thank you

Tony

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