Watching Sunsets in Exoplanet Skies

Hwan (Michelle) Bae


Daylighting in architecture is the careful use of natural lighting to reduce energy use and increase comfort, using techniques such as light shelves, reflective surfaces, and high windows. Architects on Earth have extensively utilized and researched this subject. One important aspect of daylighting is lookout. This thesis begins with an exploration of lookout in rectangular and elliptical areas to elucidate the relationship between the window ratio and the lookout value. For a circle of eccentricity e = 0, the window ratio is the same as the lookout value.

However, daylighting has not yet been applied to other planetary systems. NASA's Kepler mission has discovered more than 2000 confirmed exoplanets, hundreds of which are near Earth-sized and within the habitable zone of their host stars. Using novel visualizations, this thesis examines the apparent motion of the host star as viewed from planets beyond Earth.

Mathematica simulations model the "motion" of light inside spherical and hemispherical habitats. The simulations involve numerical integration of orbital equations of motion and analytic computation of the light beams on the walls and floors of the habitats. In some eccentric 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. Let the dominant direction be the direction of the apparent motion of the host star when the planet is at the apoapsis. Let the reversal motion be the motion in the direction opposite to the dominant direction. Let the recovery motion be the motion of the host star in its dominant direction from the end of reversal to the azimuth where reversal began. Then, the apoday is defined as the time between two consecutive noons in the dominant direction of motion, excluding the noons caused by reversal and recovery. Applications of the thesis include daylighting proposed lava tube habitats on Mars and Luna.