It’s dark outside primarily because the Sun sits low in the sky for much of the year, reducing the amount of direct sunlight reaching you and increasing the path length of sunlight through Earth’s atmosphere. This causes two main effects: shorter daylight hours and dimmer illumination during the day, especially in winter or at high latitudes. In addition, atmospheric scattering and the horizon angle make the sky appear less bright than in summer. Key factors
- Sun angle and daylight duration: In winter, the Sun’s arc is lower, so daylight hours are shorter and the Sun’s rays strike the ground at a steeper, more oblique angle, delivering less energy per unit area. This is why it feels darker earlier and later in the day and why shadows are longer. This seasonal tilt is tied to Earth’s axial tilt of about 23.5 degrees. [web results indicate discussions of seasonal daylight and sun angles]
- Atmospheric scattering: When the Sun is low, its light traverses more atmosphere, increasing scattering and absorption of blue light, which can make the sky look dimmer and more reddish near sunrise and sunset. This reduces overall perceived brightness during the day in winter. [web results discuss light scattering and sun height]
- Geographic latitude: Higher latitudes experience even shorter days and darker skies in winter, while near the equator the change is less pronounced. The phenomenon is known as the seasonal contrast in insolation. [general science understanding reflected in sources about seasons and daylight]
If you’re asking about a specific situation (e.g., in a city, at a particular date, or during an extended period of darkness like polar night), I can tailor the explanation to that location and time.
