On February 14, 1990, Voyager 1 took the first “family portrait” of the Solar System as seen from outside, which includes the image of planet Earth known as Pale Blue Dot. Soon afterward, its cameras were deactivated to conserve energy and computer resources for other equipment.
Euler is credited for popularizing the Greek letter π (lowercase pi) to denote the ratio of a circle’s circumference to its diameter, as well as first using the notation f(x) for the value of a function, the letter i to express the imaginary unit √-1, the Greek letter Σ (capital sigma) to express summations, the Greek letter Δ (capital delta) for finite differences, and lowercase letters to represent the sides of a triangle while representing the angles as capital letters.