Understanding the Physical Significance of 'a' in Kepler Orbit Equation

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    Kepler Orbit
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The equation r = a(1-e^2)/(1+e cos θ) highlights the role of 'a', the semi-major axis, as a crucial parameter in Kepler's laws of planetary motion. The numerator, a(1-e^2), indicates the maximum radial distance of the orbit, emphasizing its dependence on eccentricity 'e'. Understanding 'a' allows for insights into the average distance of an orbiting body from the central mass. The discussion also touches on alternative representations of the equation that incorporate angular momentum. Overall, 'a' serves as a fundamental measure of orbital size and shape in celestial mechanics.
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Sorry if this is in the wrong forum.

I have the equation r = \frac{a(1-e^2)}{1+e \cos \theta},
and I'm wondering what the physical significance of the numerator is.
More specifically, what is 'a' (since e is what it usually is)?

I've seen various other representations with terms like angular momentum on the top (or rather h^2/GM).

In the context of what I'm doing, it's written this way to (presumably) uncover any implicity 'e'-dependence in the orbit.
 
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'a' is the semi-major axis of the orbit, or the average value of 'r' for the orbit.
 

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