Recently reported measurements of the absorption band strength (i.e., the Einstein B-coefficient for absorption) for the transition O2(X3&Sgr;g→a1Δg) at 1.27 &mgr;m, when correctly reanalyzed in this paper, indicate that the Einstein A-coefficient for spontaneous emission of radiation is 1.47¿10-4 s-1. This is a factor of 1.75 smaller than the value of 2.58¿10-4 s-1 that has been used almost exclusively in the aeronomy field for the past 30 years. The determination of the new A-value is reviewed, with an emphasis on the derivation of the appropriate ratio of the degeneracies of the upper and lower states of this transition. The new A-value implies that ozone concentrations as inferred from measurements of O2(a1Δg) emission must be increased significantly in existing databases and also that the efficiency of solar heating in the Hartley band of ozone is larger than previously calculated. ¿ American Geophysical Union 1995