Radio astronomy and the RAS are defined in RR Article 1, RR Nos. 13 and 58 as being astronomy based upon the reception of cosmic radio waves. The aggregate of these cosmic emissions constitutes the cosmic background noise of communications engineering. Being a passive service, radio astronomy does not involve the transmission of radio waves in its allocated bands, so the use of these bands does not cause interference to any other service. On the other hand, the extreme weakness of cosmic radio emissions when compared to the strength of man-made transmissions makes radio astronomical observations very susceptible to interference from other radio services. At present, radio astronomy utilises the electromagnetic spectrum at frequencies from below 1 MHz to about 1 000 GHz, a range set primarily by the limitations of available technology. In principle, the entire radio spectrum is of scientific interest to the RAS.