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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
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] Red light is also scattered if ...
This is because long-wavelength (red) light is scattered less than blue light. The red light reaches the observer's eye, whereas the blue light is scattered out of the line of sight. Other colours in the sky, such as glowing skies at dusk and dawn. These are from additional particulate matter in the sky that scatter different colors at ...
Atmospheric refraction of the light from a star is zero in the zenith, less than 1′ (one arc-minute) at 45° apparent altitude, and still only 5.3′ at 10° altitude; it quickly increases as altitude decreases, reaching 9.9′ at 5° altitude, 18.4′ at 2° altitude, and 35.4′ at the horizon; [4] all values are for 10 °C and 1013.25 hPa ...
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 ...
when it is half moon (first/last quarter) in a dark location the sky appears like this, but with the difference that the sky appears dark blue; limiting magnitude with 12.5" reflector is 15; 6 Bright suburban sky 5.1–5.5 18.5–19.25 the zodiacal light is invisible; light pollution makes the sky within 35° of the horizon glow grayish white
The duo will appear high in the southwestern sky after nightfall and will gradually slip down toward the horizon before setting around 9 p.m., local time. An encore will be visible the following ...
[8] [15] When observing the night sky, even from moderately light polluted areas, the eye becomes nearly or completely dark-adapted or scotopic. The scotopic eye is much more sensitive to blue and green light, and much less sensitive to yellow and red light, than the light-adapted or photopic eye.