"Sunset is the daily disappearance of the sun below the horizon as a result of the Earth's rotation. The atmospheric conditions created by the setting of the sun, occurring before and after it disappears below the horizon, are also commonly referred to as "sunset".

The intense red and orange hues of the sky at sunrise and sunset are mainly caused by scattering of sunlight by dust particles, soot particles, other solid aerosols, and liquid aerosols in the Earth's atmosphere.
These enhanced red and orange colors at sunrise and sunset are mathematically explained by the Mie theory or the discrete dipole approximation. When there are no particulates in the troposphere, such as after a big rain storm, then the remaining less intense reds are explained by Rayleigh scattering of sunlight by air molecules." (wikipedia)

... not very romantic, don't you think so? :-)
anyway, I love sunsets.
and, actually, I still think they are something more than dust particles (and all that stuff) - and, yes, this is one of those case I adore to be ignorant ;-)