Rule 5b. Never use single quotation marks in sentences like the previous three. Incorrect: I had a visit from my 'friend' the tax man. The single quotation marks in the above sentence are intended to send a message to the reader that friend is being used in a special way: in this case, sarcastically. Avoid this invalid usage.
Why do jets leave a white trail in the sky? Jets leave white trails, or contrails, in their wakes for the same reason you can sometimes see your breath. The hot, humid exhaust from jet engines mixes with the atmosphere, which at high altitude is of much lower vapor pressure and temperature than the exhaust gas.
In 1946 the Skywriting Corporation found themselves with a fleet of surplus World War II planes and developed dot matrix skywriting, or skytyping. Skytyping is the process of using five planes in formation to choreograph puffs of smoke being released from each plane. The messages, written at 10,000 foot altitude, can be up to 1250 feet tall and over five miles long.