( mathematics, neologism ) An irrational constant defined as the ratio of the circumference of a circle to its radius, equal to the radian measure of a full turn approximately 6.283185307 (equal to 2π, or twice the value of π).The first one was made by the Viking Orbiter 1 spacecraft in 1980 (Duxbury and Ocampo, 1988) and brought a negative result, setting the upper limit of the normal optical depth of the putative tori to τ ≲ 3 × 10 − 5.
