This means that celestial objects in the zenith position directly above you appear in the correct position, while objects closer to the horizon appear to be higher up in the sky than they actually are.
Light rays that travel straight down do not bend, while rays that enter the Earth's atmosphere at a shallower angle get refracted and bend towards the normal, roughly following the direction of the Earth's curvature. Light from celestial objects therefore refracts multiple times when it enters the atmosphere from space.Īstronomical terms & definitions Displacing the Sun, the Moon, and the Stars The density of Earth's atmosphere is uneven-it decreases with increasing altitude. This is in contrast to terrestrial refraction that occurs when the source of light is from an object on Earth. When the light of a celestial object, like the Sun, enters the Earth's atmosphere from space, the resulting refraction is known as astronomical refraction or atmospheric refraction. If light enters a medium from another substance at a 90-degree angle, it does not refract and passes right through. The angle between the normal and the refracted light ray is known as the angle of refraction. The opposite occurs when light moves from a more dense to a less dense substance.
When light moves from a less dense to a more dense substance, like air to water or from a less dense layer of the atmosphere to a denser layer, it bends towards the normal-an imaginary line that is perpendicular to the surface of both media. How much a light wave bends depends on its wavelength, the density of the substance it is moving into, and the angle at which it hits the edge of the substance. It is also the reason why stars twinkle at night, your diamond ring sparkles, a straw or pencil in water looks bent, and the Sun can be seen even when it is technically below the horizon. It is responsible for a variety of optical phenomena including rainbows, mirages, halos, and sundogs. One of mother nature's favorite magic tricks, refraction is the bending of light as it moves from one substance to another. Refraction makes celestial objects appear higher in the sky.
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