Likewise, the path will be bent to the same extent away from the perpendicular when they exit the other side of glass. Refraction is responsible for many useful devices which bend light in carefully determined ways, from eyeglasses to telescope lenses. Refraction also causes illusions. This pencil appears to be discontinuous at the boundary of air and water. Spacecraft may appear to be in different locations in the sky than they really are.
Electromagnetic waves entering Earth's atmosphere from space are bent by refraction.
Atmospheric refraction is greatest for signals near the horizon where they come in at the lowest angle, and the apparent altitude of the signal appears to be on the order of half a degree higher than its true height. Refraction's effect on the sun adds about 5 minutes of time to the daylight at equatorial latitudes, since it appears higher in the sky than it actually is. Refraction in Earth's Atmosphere Angles exaggerated for clarity. If the signal from a spacecraft goes through the atmosphere of another planet, the signals leaving the spacecraft will be bent by the atmosphere of that planet. This bending will cause the apparent occultation, that is, the spacecraft moving into the planet's RF shadow of Earth, to occur later than otherwise expected, and to exit from occultation prior to when otherwise expected.