We flew standby recently and didn't get on the flight we hoped for. We wound up on what everybody called a "red-eye" flight from San Francisco to Medford. What is the origin of "red-eye," and what does it mean?

We flew standby recently and didn't get on the flight we hoped for. We wound up on what everybody called a "red-eye" flight from San Francisco to Medford. What is the origin of "red-eye," and what does it mean?

— Paul T., Medford

Some people insist that a red-eye flight is one that leaves late at night and arrives the next morning, Paul. Others hold that a proper red-eye involves flying west to east. That's because it's disconcerting to wind up someplace where it's hours later than it "should be" according to your internal clock.

Going the other way makes for a long day, but many people don't find it as difficult. In this sense, flying north and south is not classic red eye.

Many red-eye flights allow airlines to position planes for the next day's schedule, and passengers to connect to outgoing morning flights.

As to origins, red eyes — the literal kind — may be caused not just by lack of sleep or crying over $6 beers, but from jet lag and dehydration due to the low humidity on the plane.

And yes, anonymous inspectors from the Since You Asked Department of Aviation Research report that many people use the term these days to mean simply a late-night flight.

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