Newtonian telescope Newtonian telescope The Newtonian telescope, also called the Newtonian reflector or just the Newtonian, is a type of reflecting telescope invented by the English scientist Sir Isaac Newton (1642–1727), using a concave primary mirror and a flat diagonal secondary mirror. Newton's first reflecting telescope was completed in 1668 and is the earliest known functional reflecting telescope. The Newtonian telescope's simple design makes it very popular with amateur telescope makers. Newton's idea for a reflecting telescope was not new. Galileo Galilei and Giovanni Francesco Sagredo had discussed using a mirror as the image forming objective soon after the invention of the
Galilean transformation by Isaac Newton that provides their domain of definition. In essence, the Galilean transformations embody the intuitive notion of addition and subtraction of velocities as vectors. This assumption is abandoned in the Poincaré transformations. These relativistic transformations are applicable to all velocities, while the Galilean transformation can be regarded as a low-velocity approximation to the Poincaré transformation. The notation below describes the relationship under the Galilean transformation between the coordinates and of a single arbitrary event, as measured in two coordinate systems S and S', in uniform relative motion (velocity "v") in their common "x" and "x"′ directions, with their