A radio telescope is an astronomical instrument for receiving radio waves emitted by celestial sources. Like an optical telescope, it collects the energy from the object being studied and concentrates it to a point where it is revealed by a receiving system and then successively amplified, analysed and recorded. Radio telescopes have a much lower resolving power than optical telescopes. This is why radio telescopes of ever-increasing diameters are being built. To increase the resolving power, interferometric methods have also been used, or telescopes separated by large distances but connected to a single receiver.