Sun Horizon Time Difference Explained

The perceived time difference between the Sun's actual position at the horizon and when we see its image is primarily caused by atmospheric refraction.

Atmospheric Refraction Effect

• Earth's atmosphere acts like a lens, bending light rays from celestial objects.
• When the Sun is near the horizon (during sunrise or sunset), its light travels through a thicker layer of the atmosphere.
• This bending effect makes the Sun appear slightly higher in the sky than its actual geometric position.

Time Calculation

• Due to refraction, we see the Sun's image before it has geometrically risen above the horizon.
• Similarly, we continue to see the Sun's image for a short period after it has geometrically set below the horizon.
• This apparent advance at sunrise and delay at sunset, caused by atmospheric refraction, results in a time difference of approximately 2 minutes for each event.

Therefore, the time difference between the Sun's actual passing over the horizon and seeing its image is about 2 minutes.