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
Newtonian gauge independent, since it is the same in all gauges. In a universe without anisotropic stress (that is, where the stress–energy tensor is invariant under spatial rotations, or the three principal pressures are identical) the Einstein equation sets formula_7. Newtonian gauge In general relativity, Newtonian gauge is a perturbed form of the Friedmann–Lemaître–Robertson–Walker line element. The gauge freedom of general relativity is used to eliminate two scalar degrees of freedom of the metric, so that it can be written as where the Latin indices "a" and "b" are summed over the "spatial" directions and formula_2 is the Kronecker delta. Conformal Newtonian