Figure 23.1: This recent picture of the Andromeda Galaxy actually shows the galaxy as it
was about 2.5 million years ago. ( 35 )
field. Each of these components oscillates between positive and negative values, which is
what makes the “wavy” shape in the diagram.
Figure 23.2: An electromagnetic wave consists of oscillating electric and magnetic fields. The
distance between two adjacent oscillations is called wavelength. ( 33 )
Notice the horizontal arrow at the top left of the diagram. This measurement corresponds
to thewavelength, or the distance between two adjacent points on the wave. A related
value isfrequency, which measures the number of wavelengths that pass a given point every
second. Wavelength and frequency are reciprocal, which means that as one increases, the
other decreases.