Santa Rosa Sunset
April 15, 2003
This picture was taken in Santa Rosa, California in the fall of 2001. Just as the Sun was dipping below the horizon, the sky turned a fiery red. As mentioned in yesterday's Earth Science Picture of the Day, when the Sun is close to the horizon, whether at sunrise or sunset, the sky can quickly turn a brilliant red or orange. This is especially true if high or mid-level clouds are present. Once the Sun drops a few degrees below the horizon, only clouds above about 5,000 ft (1,540 m) are sufficiently high to intercept the final rays of sunlight. In general, the higher the cloud, the longer it will retain twilight colors.
If during the day, aerosols are introduced either by human activities or thermal currents, then the mid-range part of the visible spectrum (green colors) may be more readily attenuated, leading to deeper reds at dusk. Salt spray from the Pacific Ocean, a common aerosol along the West Coast of the U.S., quite often enhances sunset colors.