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asinh magnitude Magnitudes within the SDSS are expressed as inverse hyperbolic sine (or "asinh") magnitudes, sometimes referred to informally as luptitudes . The transformation from linear flux measurements to asinh magnitudes is designed to be virtually identical to the standard astronomical magnitude at high signal-to-noise ratio, but to switch over to linear behavior at low S/N and even at negative values of flux, where the logarithm in the Pogson magnitude fails. Details can be found in the Lupton et al. 1999 AJ paper.