One of the most legendary PR disasters in the history of astronomy happened in 1973 when the world awaited the arrival of comet Kohoutek, discovered by Czech amateur astronomer Luboš Kohoutek early that year. Once the orbit was plotted, astronomers knew that the comet was a first time visitor from the hypothesized Oort Cloud, a gigantic 2 light-year wide freezer containing pristine ices from the early solar system.
Because this was a virgin comet, untouched by intense sunlight for billions of years, the prediction was that it had lots of fresh ices ready to boil off once it entered the inner solar system. It was called the "comet of the century" by one enthusiastic astronomer. The name stuck. People lined up at planetariums and amateur telescope sales soared.
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But Kohoutek was a dud, never rising to the expected brightness, though it became a modest naked–eye object. The letdown was such a publicity bust it killed news coverage of comets until the legendary Halley's comet came along in 1986.