Flying west? Watch the northwestern sky out your plane window…

If you are flying west across the United States this summer, leaving just at or after sunset, find Venus bright and low in the northwestern sky and see how long it takes to set.

I had the good fortune once to notice the planet Venus just above the western horizon out my window. Normally, Venus would have set in an hour or so, but I was able to watch it set over several hours. Why?

As the aircraft flies westward at 500 mph, it is almost as fast as the earth’s rotation of about 700 mph at mid-latitudes. If you think about it, if the plane flew at the same speed as the earth’s rotation, the sun and stars would appear not to move in the sky. You can use this effect to watch the planet Venus, and around Memorial Day weekend the planets Jupiter and Mercury, very slowly set. In May, Jupiter is low in the west after sunset, sinking out of sight in early June, leaving Venus and Mercury together through mid-June. Venus is a solo show low in the west through fall.

So, if you are flying westward, you are lucky because time, as measured by the sun and stars, appears to slow down (a supersonic jet would land “before” it took off, based on local time at the departure and arrival cities). You would be doubly fortunate to see the planets hang out for a long time if you are flying westward after sunset.


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