This photo sequence taken in Veszprem, Hungary, shows the colour variability of the setting sun. As you can see, the Sun transitions from a golden orange colour to a deeper red as it sinks away into the horizon. This colour transition is the result of the increasing path length of sunlight. At sunset, light must travel further through the atmosphere before it reaches your eyes- because of this increase in path length, more light is reflected and scattered. As a result, the Sun will appear dimmer and the colour appears to change. This occurs simply because the shorter wavelength colours like blue and green are being preferentially scattered from our view. What remain are the longer wavelengths colours (orange and red) so this is what we see.
Photo details: Konica-Minolta Dynax 5D camera; 300mm Sigma lens; f/6.3; exposures from 1/3200 (brightest Sun) to 1/250 (darkest Sun) seconds.