After sunset as the sun sinks further below the western horizon, a dark band rises up along the horizon in the east. Its edge is suffused with a pink glow - the Belt of Venus or Anti-twilight Arch.
The dark band is unlit air that is shadowed from the sun’s rays by the bulk of the Earth itself.
If you were in an aircraft crossing the shadow’s edge you would see the high altitude sun setting. Like in all sunsets its rays are reddened by Rayleigh scattering. Air molecules preferentially scatter shorter wavelength light to give blue sky and blue denuded direct rays.
The reddened rays light the atmosphere along the shadow edge. Combined with more scattered blue light they form the pinks of the Belt of Venus.
|
