Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2017/iii/paper-316/1/vi/solution

On the corrected steady phase-mixed orbit, each fragment crosses a fixed orbital longitude once per orbital period. Hence the cross-sectional-area current through that point is
From the fractional luminosity of a phase-mixed eccentric wire, . Therefore the area rate at the foreground crossing of the line of sight is
Only the foreground segment blocks the star; the far-side intersection does not add another occultation current. The orbital area current is constant because the line density varies as , even though the local orbital speed varies.

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