Question

Imagine that you were sitting at the beach and you are watching a beautiful sunset over the ocean. Just before the Sun disappears from sight, is the top of the Sun actually above or below the horizon?

In other words, if the Earth's atmosphere were removed, would the Sun still be visible or would it actually be below the horizon? Explain what's happening here with good physics. Note that the effects of the answer to this question are indeed accounted for when accurate sunset (and sunrise) times are provided. Also, spacecraft orbiting other planets will typically observe sunrise and sunset as they orbit the planet. The same effects can tell us useful information about the atmosphere of the host planet.

Answer 1

The Sun rise can be seen on Earth nearly 2 minutes before Sun reaches the Horizon .The reason for this is refraction of light. The light from Sun travels through atmosphere of Earth where the density of air is steadily increases as Light reaches closer and closer to Earth. Thus Light traverses from Lighter medium to denser medium ( e.g from air to glass) in this case and hence light bends towards normal as they travel through atmosphere thus appearing to come from horizon.

Similarly at Sunset the Light will appear for 2 additional minutes even after it goes below Horizon due to refraction of Light in Earth's atmosphere even though Sun is actually below the Horizon.

In case Earth had no atmosphere at all,then Sun would appear on Earth only when  it comes to same level as the Horizon and not later ( at Sunset) or earlier (at Sunrise)