(Warning: spoilers ahead /s)

When the monolith is uncovered on the moon in 2001: A Space Odyssey, it generates a massive, but brief radio signal when it is illuminated by the Sun for the first time.

Given that:

  • The signal lasted no more than 30 seconds
  • The time and date of the exposure to the Sun was effectively random
  • No one expected the monolith to generate any sort of signal

How did anyone know that this signal was directed towards Jupiter (in the movie), or Saturn (in the book)?

  • 1
    I just assumed the signal from the Lunar monolith caused the Jupiter one to signal - and when that one was detected they realized the Lunar one had contacted it and said aimed at Jupiter as shorthand. Commented Aug 23, 2023 at 18:25
  • How a monolith can generate a narrow signal and aim it is a mystery. It might be linked with the other monoliths. But a monolith is basically a super computer / quantum computer so calculating where Jupiter (or Saturn) is should not be difficult. My understanding is the light show / life in a room at the end isn't a Cosmos style wormhole - it is Dave getting entangled into the supercomputer. Commented Aug 23, 2023 at 18:34
  • @lucasbachmann In the movie, they didn't even know that the Jupiter monolith existed until Bowman saw it first hand.
    – Peter M
    Commented Aug 23, 2023 at 18:46
  • Maybe (even probably I'll acknowledge you may be right) - the short mission brief when HAL is being shutdown only mentions the Lunar one - but it begs the question of what the crew was planning to do out there. Inspect every moon of Jupiter for anomalies? In a later book when Jupiter ignites Europa gets a monolith to uplift the squid aliens. So it was a possibility they were expecting to find another one. Commented Aug 23, 2023 at 18:54
  • "In a later book when Jupiter ignites Europa gets a monolith to uplift the squid aliens" .. one of those great sentences one only sees in sci-fi discussions!!!
    – Fattie
    Commented Aug 25, 2023 at 13:04

1 Answer 1


In the novel, it is clear that the transmission is picked up by a series of probes, which allowed the direction and destination to be picked up.

And now Deep Space Monitor 79 had noted something strange - a faint yet unmistakable disturbance rippling across the Solar System, and quite unlike any natural phenomenon it had ever observed in the past. Automatically, it recorded the direction, the time, the intensity; in a few hours it would pass the information to Earth. As, also, would Orbiter M 15, circling Mars twice a day; and High Inclination Probe 21, climbing slowly above the plane of the ecliptic; and even Artificial Comet 5, heading out into the cold wastes beyond Pluto, along an orbit whose far point it would not reach for a thousand years.

‘After all these ages, one would naturally assume that it was inert. But soon after lunar sunrise, it emitted an extremely powerful blast of radio energy. We believe that this energy was merely the by-product - the backwash, as it were - of some unknown form of radiation, for at the same time, several of our space-probes detected an unusual disturbance crossing the Solar System. We were able to track it with great accuracy. It was aimed precisely at Saturn.

  • 2
    This definitely wasn't covered in the movie, which I just re-watched after many years. I'm not even sure that I read the book.
    – Peter M
    Commented Aug 23, 2023 at 16:04
  • Very long time since I watched the movie so couldn't comment on that source. Book was helpfully a lot more explicit (not entirely surprising from Clarke).
    – Michael
    Commented Aug 23, 2023 at 16:45
  • 2
    I would add a note that the movie replaced Saturn with Jupiter as the destination.
    – Rad80
    Commented Aug 24, 2023 at 12:17
  • 2
    @Rad80 The movie was released before the novel. Commented Aug 25, 2023 at 0:08
  • 3
    @Acccumulation Both the book and the movie were developed contemporaneously. The difference in destination from Saturn to Jupiter is discussed in this question, and it comes down to the film people not having suitable images of Saturn's rings.
    – Peter M
    Commented Aug 25, 2023 at 13:29

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