Electromagnetic radiation and B fields in EMR are in-phase (see math section below). An important aspect of light's nature is its frequency. The frequency of a wave is its rate of oscillation and is measured in hertz, the SI unit of frequency, where one hertz is equal to one oscillation per second. Light usually has multiple frequencies that sum to form the resultant wave. Different frequencies undergo different angles of refraction, a phenomenon known as dispersion. A wave consists of successive troughs and crests, and the distance between two adjacent crests or troughs is called the wavelength. Waves of the electromagnetic spectrum
Bowditch Crests Bowditch Crests Bowditch Crests () is a line of precipitous cliffs surmounted by four summits on Bermel Peninsula in eastern Graham Land. The feature was photographed from the air by Lincoln Ellsworth in November 1935 and was mapped from these photos by W.L.G. Joerg. It was surveyed by the Falkland Islands Dependencies Survey in 1958, and named by the UK Antarctic Place-Names Committee for Nathaniel Bowditch, American astronomer and mathematician, author of "The New American Practical Navigator" (1801) which firmly set out the practical results of theories established at that date and has since gone through more than 56 editions.