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 combination (formula_14) of groups is required. Here, we only look at the Lie algebra of the Galilean group; it is then easy to extend the results to the Lie group. The relevant Lie algebra is spanned by and (an antisymmetric tensor), subject to commutation relations, where This Lie Algebra is seen to be a special classical limit of the algebra of the Poincaré group, in the limit . Technically, the Galilean group is a celebrated group contraction of the Poincaré group (which, in turn, is a group contraction of the de Sitter group "SO"(1,4)). Renaming the generators of the latter