= Equatorial plane
{title2=$\theta=\pi/2$}
Given a polar axis, the <equatorial plane> passes through the <sphere>'s centre and is perpendicular to that axis. In <spherical coordinates> with <polar angle> $\theta$, it is the plane $\theta=\pi/2$. For motion in a spherically symmetric gravitational field, conservation of <angular momentum> permits rotation of axes so that a nonradial orbit lies in such a plane. This is a choice of <orientation>, rather than an additional physical restriction on a spherically symmetric problem.
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