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If light sources (e.g. the Moon and light pollution) were removed from the night sky, only direct starlight would be visible. The sky's brightness varies greatly over the day, and the primary cause differs as well. During daytime, when the Sun is above the horizon, the direct scattering of sunlight is the
That is, the light of each shell adds to the total amount. Thus the more shells, the more light; and with infinitely many shells, there would be a bright night sky. While dark clouds could obstruct the light, these clouds would heat up, until they were as hot as the stars, and then radiate the same amount of light.
Scattering effects also partially polarize light from the sky and are most pronounced at an angle 90° from the Sun. Scattered light from the horizon travels through as much as 38 times the air mass as does light from the zenith, causing a blue gradient looking vivid at the zenith and pale near the horizon. [9]
only hints of zodiacal light are seen on the best nights in autumn and spring; light pollution is visible in most, if not all, directions; clouds are noticeably brighter than the sky; the Milky Way is invisible near the horizon, and looks washed out overhead. The winter Milky Way, even directly overhead, is fairly subtle.
When the Sun is located at the zenith, the band of maximal polarization wraps around the horizon. Light from the sky is polarized horizontally along the horizon. During twilight at either the vernal or autumnal equinox, the band of maximal polarization is defined by the north-zenith-south plane, or meridian. In particular, the polarization is ...
Morning sky: Very bright Venus rises in the east around 5 a.m. in early January and around 6 a.m. late in the month. Mercury and Mars joined Venus low in the east in late December.
The sun sends more than heat and light to Earth — it sends energy and charged particles known as the solar wind. But sometimes that solar wind becomes a storm. The sun's outer atmosphere occasionally “burps” out huge bursts of energy called coronal mass ejections.
Walker's Law has been verified by observation [13] [9] to describe both the measurements of sky brightness at any given point or direction in the sky caused by a light source (such as a city), as well as to integrated measures such as the brightness of the "light dome" over a city, or the integrated brightness of the entire night sky. At very ...