Atmospheric diffraction regularly with a 6 watt transmitter from the middle of the Pacific. For more details see the "communications" part of the "Kon-Tiki expedition" entry in Wikipedia. An exotic variant of this radio wave propagation has been examined to show that, theoretically, the ionospheric bounce could be greatly exaggerated if a high powered spherical acoustical wave were created in the ionosphere from a source on earth. In the case of sound waves travelling near the Earth's surface, the waves are diffracted or bent as they traverse by a geometric edge, such as a wall or building. This phenomenon leads to a
First observation of gravitational waves be detected indirectly – by observing celestial phenomena caused by gravitational waves – or more directly by means of instruments such as the Earth-based LIGO or the planned space-based LISA instrument. Evidence of gravitational waves was first deduced in 1974 through the motion of the double neutron star system PSR B1913+16, in which one of the stars is a pulsar that emits electro-magnetic pulses at radio frequencies at precise, regular intervals as it rotates. Russell Hulse and Joseph Taylor, who discovered the stars, also showed that over time, the frequency of pulses shortened, and that the stars were gradually spiralling