Technologies in 2001: A Space Odyssey well, such as a nervous breakdown—as Hal did in the film. Clarke noted that, contrary to popular rumor, it was a complete coincidence that each of the letters of Hal's name immediately preceded those of IBM in the alphabet. The meaning of HAL has been given both as "Heuristically programmed ALgorithmic computer" and as "Heuristic ALgorithmic computer". The former appears in Clarke's novel of "2001" and the latter in his sequel novel "2010". In computer science, a heuristic is a programmable procedure not necessarily based on fixed rules, producing informed guesses often using trial-and-error. The results can be false such
Technologies in 2001: A Space Odyssey perfect alignment.). Similarly, during the scene in the Dawn of Man, where the sun is seen above the monolith, a crescent moon is depicted close by in the sky. During this phase of the lunar cycle the moon would be "new" and therefore be invisible. Finally, the edge of Earth appears sharp in the movie, when in reality it is slightly diffuse due to the scattering of the sunlight by the atmosphere, as is seen in many photos of Earth taken from space since the film's release. The sequence in which Bowman re-enters "Discovery" shows him holding his breath just