Some of the moons in the Solar System are tidally locked, meaning the same side of the moon’s surface faces its planet at all times. This document explores the implications of such a phenomenon on the day-night cycle of life on the moon Europa.

Daylight Cycle on Europa

On the side of Europa facing Iovis, the gas giant occupies a fixed point in the sky while the sun rises and sets over a period of roughly 85.2 hours. Europan orbital periods are divided roughly into four phases of 21 hours each. The world’s orbit also determines the angle of the sun, so a full tide-cycle is made up of two daylight periods and two nightlight periods separated by rest periods. At some point during the day, the sun passes behind Iovis itself and causes a solar eclipse.

  1. Dawntide to First Rest

Europa stirs several hours before dawn. Iovis wanes in the sky, heralding the rising Sun. The first ten hours of daylight are a burst of renewed activity for the planet and its inhabitants. Travelers seek shelter and rest from the relentless Sun toward the end of this period. Bright tents with black-out curtains are raised in the wilderness and her people go down for their first rest period of the cycle.

  1. Eclipse to Second Rest

Europans wake to observe the Iovian eclipse and the highest tides. Both the sky and Iovis itself are at their darkest, and the ocean is at its most dangerous, until after three hours the Sun reemerges from behind the giant to light the way again. Travelers take a second rest period several hours later as its seas ebb.

  1. Dusktide to Third Rest

Europa stirs again to observe the setting Sun. As daylight sinks below the horizon, Iovis waxes to half-full and begins to illuminate the night sky. Travelers move in the softly increasing glow of Iovis and the receding tides, entering another rest period shortly before low-tide.

  1. Nighttide to Fourth Rest

Europa wakes to observe a full-phase Iovian globe illuminating the mid-point of the night. These are the last twenty hours of a tidal cycle, and as Iovis slowly wanes travelers move for some fourteen hours before they enter their last rest period and prepare for the coming dawn-tide and the rising Sun.