Could you drive fast enough to keep a sunset in view?

A truck driver asked us this question. If you could drive fast enough, could you keep a sunset continually in view?

The answer depends on the speed of Earth’s rotation – or, more specifically, on the speed at which Earth spins you around at your precise location on the globe.

People at Earth’s equator are spun toward the east at about about 1,000 miles per hour. So that’s how fast you’d have to drive to keep a sunset continuously in view if you were driving along an equatorial highway.

The speed of sound at sea level is about 800 miles an hour. So, to keep the sunset in view – as seen from the latitude of the equator – you’d have to drive your car fast enough to break the sound barrier. Supersonic aircraft can do this!

But the speed of Earth’s spin varies as you go north or south from the equator. At latitudes north or south of the equator, you go around more slowly due to the rotation of the Earth. In the northern U.S. or Canada, for example, you’re moving at only about about 700 miles an hour, thanks to Earth’s spin.

Or imagine standing at the North Pole around the time of the spring or fall equinox.

Around that time, you’d see the sun barely located above your horizon. The sun would be moving in a circle around your horizon as seen from the North Pole – a continuous 24-hour sunset – with no driving necessary!

Visit EarthSky Tonight for easy-to-use night sky charts and info. Updated daily.

September 13, 2009

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