Ask Clay: You don't see jet contrails at night because it's dark

Today’s question:

I have a question about contrails left by airplanes. During the day you see lots of them, but looking up on a moonlit night you don’t see any. Is this because planes don’t form them at night or you just can’t see them?

I take up this question with some hesitation because invariably some of you people are going to want to talk about the imaginary chemtrails — the stuff the government sprays on us or uses to sterilizes us or brainwash us or whatever.

My favorite nutcase idea about contrails came from a reader who once told me with some confidence that two contrails crossing at right angles are a bullseye for satellites aiming lasers or death rays or whatever at us.

Sigh.

Anyway about contrails, which of course are formed when jet exhaust hits the cold air of the upper atmosphere:

The main reason you don’t see them at night is because it’s dark out there. Also, there are a fewer big jets flying at night.

You can find plenty of pictures of nighttime contrails online.

Why is the tarmac at airports called tarmac?

Back in the 1820s a Scottish inventor named John L. McAdam came up with a method of covering roads with crushed stone, especially granite.

In 1902 an English inventor, Edgar Purnell Hooley, improved on the idea when he patented tarmacadam, a surface made by spraying tar over crushed stone.

Tarmac quickly became a catchall name for paved surfaces, especially airport runways.