Re: At what speed would you fly to keep a constant sunset on your horizon?

Andy,

Thank you for the question.

Your question is one way of asking how fast the the surface of the Earth moves due to its rotation around the polar axis. The Earth's rotation causes the apparent motion of the Sun across the sky and gives us sunsets and sunrises.

The sun setting in the west is caused by the movement of the Earth's surface toward the east. To counteract this surface motion an airplane would have to move with a velocity toward the west, and the sunset, with a speed equal to the speed of the Earth's surface.

Since the Earth is nearly a sphere, different parts move at different speeds at it rotates. The fastest parts are on the Equator, the slowest parts are at the North and South Poles and don't really have any velocity at all as we are defining it.

For the Equator just divide the circumference of the Earth in your favorite units by the 24 hours it takes for the Earth to rotate. I get something like 1,600 kilometers per hour for the speed of the Earth's surface on the Equator. This means an airplane would have to fly at this speed toward the west in order to keep up with the setting sun. The Concorde could do it, but the average passenger jet could not.

At the North Pole near the date of the Autumnal Equinox (Sept. 20-21) the sun is setting and on the horizon all day. You don't need to move to keep up with it.

The figures and dates are somewhat approximate, but I hope they are close enough for you purposes. One factor I have not considered is that the axis of rotation is not perpendicular to the plane of the orbit of the Earth. This means that the plane may not always be flying due west to keep up with the sunset.

Best Regards,

Everett Rubel