1. The difference between the angular positions of the image and object of a celestial object that results from refraction in the earth's atmosphere. Astronomical refraction is greatest near the horizon where it normally exceeds a solar diameter. Consequently, we see the image of the sun above the horizon even though the sun itself is below, and this extends the length of the day measurably at both ends. 2. A variety of phenomena that result from the refraction of celestial light by the earth's atmosphere. It is distinguished from the term terrestrial refraction, which is used when the source is within our atmosphere.