Newtonian telescope secondary mirror. This design reduces the size and cost of the telescope with a shorter overall telescope tube length (with the corrector extending the focal length in a "telephoto" type layout) combined with a less costly spherical mirror. Commercially produced versions of this design have been noted to be optically compromised due to the difficulty of producing a correctly shaped sub-aperture corrector in a telescope targeted at the inexpensive end of the telescope market. 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
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