Baptism of light. During dawn the incidence angle of the sunrays through the atmosphere is very low. Scattering processes at such long paths at air molecules entitled after Lord Rayleigh causes the shortwave blue to be almost completely gone and hence the sky appears red at the horizon. In contrast the zenith appears in deep violet. This is caused by the ozone layer that acts like a color filter. The sunlight moves almost parallel through the stratosphere. Here, the ozone layer absorbs up to 40% of the green and yellow spectrum of the visible light. Without the ozone layer the sky would turn green during dusk and dawn. Venus is still high in the sky and is almost visible until sunrise.
Canon 20D, EF-L 24-105mm, f/22, 16sec, ISO 100, polarization filter, tripod