For some eccentric planetary orbits, the host star appears to move backwards in the sky as the orbital speed momentarily exceeds the rotation speed near the periapsis, when the planet is nearest to its star. This necessitates a new definition of a day. Thus, a new definition “Apoday” is defined as the time between two consecutive noons in the dominant direction of motion of the host star, excluding the noons caused by its reversal and recovery. This thesis begins with an exploration of conditions necessary for apoday to happen.

Over the past decade, NASA’s Kepler and K2 missions have discovered thou- sands of planetary candidates for human settlement, of which 2000 have been confirmed. If humans settle on the moon, planets, or exoplanets, how sunset looks like on exoplanet? This thesis examines the apparent motion of the host star as viewed from exoplanets. Mathematica simulations model the motion of the host star. The simulations involve numerical integration of orbital equations of motion and analytic computation of the altitude of the sun observed from the planet. For the special case of zero obliquity(tilt), an exact nonlinear equations delimiting apodays in the space of orbital eccentricity and spin-orbit (day-year) ratio is derived, confirmed by numerical simulations.


Linder, John

Second Advisor

Rober, Kelvey


Mathematics; Physics


Astrophysics and Astronomy | Physical Sciences and Mathematics



Publication Date


Degree Granted

Bachelor of Arts

Document Type

Senior Independent Study Thesis



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