Horizon, an apparent line separating the sky from the earth, which retreats as one approaches it.

“Communism is already visible on the horizon,” declared Khrushchev in a speech. Question from the floor: “Comrade Khrushchev, what is a ‘horizon’?” “Look it up in a dictionary,” replied Nikita Sergeevich. At home the questioner found the following explanation in a reference work: “Horizon, an apparent line separating the sky from the earth, which retreats as one approaches it.”

• Koselleck, Future Past (2004) p.261