Studies of gas in galaxies reveal not only the gasΓÇÖs structure but also its motion. This false color image of the H I gas in Maffei 2 is color-coded to indicate velocity: red for gas that is moving away from us, and blue for gas that is moving toward us. Velocity is determined by carefully observing the wavelength of the H I radio emission. Because of the Doppler shift, the exact wavelength depends on the speed and direction the gas is moving: if toward us, the wave- length will be slightly reduced; if away, it will increase. The colors in this image tell us the gas is moving as if in a rotating disk. One side of the disk is coming toward us, while the other side is moving away.
Of course, the motion of H I in Maffei 2, as in most galaxies, is
