Day length

Day length is the interval between sunrise and sunset at a given location and date. It varies with latitude, season, and the Sun’s apparent path across the sky.

Earth's axial tilt: Earth's rotational axis is inclined about 23.4 degrees relative to the perpendicular to its orbital plane. The tilt shifts the Sun’s seasonal path, lengthening days in one hemisphere while shortening them in the other.
Solar day: A solar day is the interval between successive passages of the Sun across a local meridian. Day length is a portion of the solar day, not the full rotation-to-rotation interval.
Photoperiodism: Photoperiodism is the biological response of organisms to the relative lengths of day and night. Plants and animals use seasonal daylight changes to time growth, reproduction, and migration.
Twilight: Twilight is the interval when sunlight illuminates the atmosphere before sunrise or after sunset. It provides usable ambient light beyond the sunrise-to-sunset interval.
Solar declination: Solar declination is the angular distance of the Sun north or south of the celestial equator. Its changing value sets the Sun’s daily arc and therefore the daylight interval.
Horizon: The horizon is the apparent boundary separating the sky from the ground or sea. Sunrise and sunset are defined by the Sun’s position relative to this boundary.
Photoperiodic flowering: Photoperiodic flowering is the control of flowering time by the duration of light and darkness. Day length acts as a seasonal cue for flowering in many plant species.
Night: Night is the period when the Sun is below the horizon at a location. It is the complementary interval to daylight within a daily cycle.
Latitude: Latitude is the angular position of a place north or south of Earth’s equator. At higher latitudes, seasonal changes in daylight become more pronounced.
Solar altitude: Solar altitude is the angle of the Sun above or below the horizon. Daylight lasts while the Sun’s apparent altitude meets the chosen sunrise and sunset threshold.

Linked from 15 pages