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This includes direct sunlight, diffuse sky radiation, and (often) both of these reflected by Earth and terrestrial objects, like landforms and buildings. Sunlight scattered or reflected by astronomical objects is generally not considered daylight. Therefore, daylight excludes moonlight, despite it being reflected indirect sunlight.
Starry sky crossed with the Milky Way and a meteor. Starlight is the light emitted by stars. [1] It typically refers to visible electromagnetic radiation from stars other than the Sun, observable from Earth at night, although a component of starlight is observable from Earth during daytime.
The polar circle (at 66°33′50.3″ north or south) is defined as the lowest latitude at which the Sun does not set at the summer solstice. Therefore, the angular radius of the polar circle is equal to the angle between Earth's equatorial plane and the ecliptic plane. This period of time with no sunset lengthens closer to the pole.
UV rays, and therefore sunlight and sunlamps, are the only listed carcinogens that are known to have health benefits, [55] and a number of public health organizations state that there needs to be a balance between the risks of having too much sunlight or too little. [56] There is a general consensus that sunburn should always be avoided.
Brightest sunlight Luminance. This section lists examples of luminances, measured in candelas per square metre and grouped by order of magnitude. Factor
In direct sunlight the movement of the sun can be recorded and observed using a sundial that casts a shadow that slowly moves during the day. Other planets and natural satellites that rotate relative to a luminous primary body, such as a local star, also experience daytime, but this article primarily discusses daytime on Earth.
At civil twilight, the center of the Sun's disk appears to be between 1/4° and 6° below the horizon. At nautical twilight, the Sun's altitude is between –6° and –12°. At astronomical twilight, the Sun is between –12° and –18°. When the Sun's depth is more than 18°, the sky generally attains its maximum darkness.
Twilight is the time period between dawn and sunrise, and between sunset and dusk. Morning twilight: astronomical, nautical, and civil stages at dawn. The apparent disk of the Sun is shown to scale. [1] Evening twilight: civil, nautical, and astronomical stages at dusk. The solar disk is shown to scale.