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For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.
Light rays coming from the zenith take the shortest-possible path (1 ⁄ 38) through the air mass, yielding less scattering. Light rays coming from the horizon take the longest-possible path through the air, yielding more scattering. [11] The blueness is at the horizon because the blue light coming from great distances is also preferentially ...
Diagram showing displacement of the Sun's image at sunrise and sunset Comparison of inferior and superior mirages due to differing air refractive indices, n. Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of height. [1]
Most of the UV in the mid-range of energy is blocked by the ozone layer, which absorbs strongly in the important 200–315 nm range, the lower energy part of which is too long for ordinary dioxygen in air to absorb. This leaves less than 3% of sunlight at sea level in UV, with all of this remainder at the lower energies.
Light has to pass through a larger part of the atmosphere when the sun is lower on the horizon. Red, orange and yellow have longer wavelengths, which means, in short, they have a better chance of ...
Bradley uses this fact to estimate the speed of light in air or vacuum, and his result is more accurate than Huygens’s: about 3.0×10 8 m/s in modern units. For the first time, the measurement is correct to the first two significant figures.
The northern lights are expected to be strongest between Friday, Jan. 31, and Saturday, Feb. 1. The best time to view them is from 10:00 p.m. and 2 a.m. local time.
Figure 2: Foucault's determination of the relative speed of light in air vs water. Light from a passing through a slit (not shown) is reflected by mirror m (rotating clockwise around c) towards the concave spherical mirrors M and M'. Lens L forms images of the slit on the surfaces of the two concave mirrors. The light path from m to M is ...