What Are Daylight Hours? Definition and Seasonal Variation

Daylight hours = the period when the Sun is above the horizon, providing natural illumination.

What Drives Variation

• Axial tilt (23.44°): Causes seasons
• Latitude: Determines extremes
• Orbit position: Solstices/equinoxes

Patterns by Latitude

• Equator (0°): ~12 hours year-round (± minutes)
• Mid-latitudes (e.g., 40°N – New York, Madrid): 9h (winter) to 15h (summer)
• Arctic Circle (66.5°N): 0h (polar night) to 24h (midnight sun)
• Poles: 6 months day / 6 months night

Practical Definitions

• Civil twilight: Sun 0°–6° below horizon (outdoor activities possible)
• Nautical twilight: 6°–12° (navigation at sea)
• Astronomical twilight: 12°–18° (dark enough for astronomy)

Daylight length affects circadian rhythms, agriculture, energy use, and mood (SAD). Modern tools (timeanddate.com, NOAA) provide precise tables for any location/date.