The Sentinel is a story about the loneliness of existence. It is set on the moon in 1996, let’s say 2096. An astronaut geologist on an exploration team is exploring a huge barren tract of the moon. Daylight lasts for a week. The team are exploring a wasteland. The explorers’ days are dictated by routine, at the end of every 16 hours, they retire for eight hours, wake, cook breakfast. One day, the geologist spots the sunlight glinting off something in the distant mountains. It’s not uncommon for the sun to glint off a rock face there, but the geologist wishes to investigate, despite the fact that everyone thinks he is wasting his time and that he will be the laughing stock of the mission.
He convinces the team to go though, and having climbed the mountain, he finds at its top, a shining pyramid twice the height of a man.
The pyramid is returned to Earth. It takes twenty more years to take it apart and reach the machine within the walls. The geologist realises they have taken apart a beacon placed by another intelligent civilization that had been left on the hope that life would form on Earth. Now that the beacon has been moved, its signal will have been sent to whatever was detecting it. As the geologist concludes, ‘we have set off the fire-alarm, and have nothing to do but to wait.’
Clarke explores the vastness of the universe and correlates it to the loneliness we have as an intelligent species. The loneliness of the aliens, whoever or whatever they are, is also felt. The civilization that has scattered thousands of the pyramid sentinels near every planet that could support life around the galaxy.
This story was expanded to become the basis for Stanley Kubrick’s 2001: Space Odyssey, but I have seen Space Odyssey and though that was a great film, I wouldn’t want to compare or contrast it with this story. They are entirely different. The Sentinel should be read as it is, but I can see how it gripped the imagination of that great film maker, as it is bound to impress anyone who reads it.