Variability in the Astronomical Refraction of the Rising and Setting Sun

Abstract

Observed timings of 244 sunrises and 135 sunsets from two closely spaced geographic locations in Edmonton, Alberta, were used to determine astronomical refraction for the Sun's upper limb. The observed astronomical refraction had a mean of 0 669, a standard deviation of 0 175, and a range between 0 402 and 2 081. At sunrise, the astronomical refraction had a mean of 0 714, a standard deviation of 0 184, and a range between 0 402 and 2 081. At sunset, the astronomical refraction had a mean of 0 579, a standard deviation of 0 108, and a range between 0 442 and 1 085. There is a strong annual variation of the monthly mean and the monthly standard deviation of the astronomical refraction. Both parameters reach a maximum during the coldest months for sunrises and sunsets. Abnormally large refraction events—sometimes called Novaya Zemlya solar mirages—can occur in both warm and cold months.