Dear Tom,
There is daylight prior to and after the published times for sunrise and sunset. Is this because of the time it takes the sun’s light to reach the Earth?
Bonnie Maric
Dear Bonnie,
At the speed of light, sunlight takes about nine minutes to travel from the sun to the Earth. However, sunrise and sunset times on Earth are not dependent upon the time when light leaves the sun.
Daylight is longer than it should be by about five minutes because sunrise is defined as the moment the upper rim of the rising sun is first visible (“first light”), and sunset as the last moment. At sunrise, it takes about two minutes from first light to full solar disk, and about another two minutes reversing the process at sunset. Twilight, the period of illumination an hour or more before sunrise and after sunset, results from sunlight that shines on the upper atmosphere being scattered back to the Earth’s surface.
