These concerns are because at polar latitudes, summer solstices feature the midnight sun and winter solstices have polar night. These natural phenomena occur because the earth's axis tilts toward the sun in summer and away from the sun in winter, causing the poles to be exposed to the sun's rays for six months each, non-stop. The reason most of the earliest Muslims did not experience these phenomena during Islam's early days is because they did not live in polar regions, but in the Subtropics, where the Sun can be directly overhead and does set at night.