Terrestrial refraction

place holder DRAFTING

Uncertainty, precision, model accuracy, predictive power

"Every one conversant with nautical astronomy is aware that some uncertainty always attends observations made with the natural horizon, from the varying amount of the dip occasioned by terrestrial refraction. The cause of these variations is very obscure. The best authorities seem to regard differences of temperature in the air and water as the sole cause of the irregular density of the lower strata of the atmosphere on which the varieties of the dip depend. It is known that, in general, when the water is warmer than the air, the dip is greater than that given in the tables; and that when the water is colder than the air, the dip is less. But cases occur where the deviations from the tables are found to bear little relation, at least in amount, to the relative temperatures of the air and water. Some other property of the atmosphere must, therefore, be sought after, by the influence of which the effects of temperature are modified."

Young

Citing {Brinkley, J. 1815, Trans. R. Irish Acad., 12, 77} "It is well known to those conversant in observations made with good instruments that near the horizon an irregularity in refraction hitherto unexplained shews itself." ‘‘it is not likely the irregularities will ever be submitted to any law, and investigations respecting formulae for refractions for zenith distances greater than about 80� may be considered more curious than useful’’

Citing d, Ivory (1823) ‘‘The refractions are ... affected by circumstances of which the observer has no intimation, and which cannot enter into any theory. The real causes of such anomalies is [sic] undoubtedly the irregular changes that take place in the remote parts of the atmosphere, which are not indicated by the barometer or the thermometer.’’

Citing

Himself "Refraction within about 5° of the horizon is so variable that no a priori formula or table can be expected to give accurate values there."

"Refraction within about 5° of the horizon is so variable that no a priori formula or table can be expected to give accurate values there; the local lapse rate and thickness of the boundary layer above the observer must be known. "

"At and below the astronomical horizon, the refraction depends primarily on atmospheric structure below the observer and varies so much (tens of minutes, or even several degrees) that only very crude predictions can be made."

Burton "Atmospheric refraction is both an astronomical irritant and an intellectual puzzle. A major problem for observational astronomers since Ptolemy, it still baffled Newton who consumed nearly a year of his life finding a correct understanding of the problem in order to aid the astronomer John Flamsteed. 1 Despite its complexity, it has been a delightful puzzle for students of optics and mathematics, and for the armchair astronomer. "