The Sentinel (short story)

"The Sentinel" was written in 1948 for a BBC competition (in which it failed to place) and was first published in the magazine 10 Story Fantasy in its Spring 1951 issue, under the title "Sentinel of Eternity". It was subsequently published as part of the short story collections Expedition to Earth (1953), The Nine Billion Names of God (1967), and The Lost Worlds of 2001 (1972). Despite the story's initial failure, it changed the course of Clarke's career.

The Sentinel (published 1982) is also the title of a collection of Arthur C. Clarke short stories, which includes the eponymous "The Sentinel", "Guardian Angel" (the inspiration for his Childhood's End), "The Songs of Distant Earth", and "Breaking Strain".

The story deals with the discovery of an artifact on Earth's Moon left behind eons ago by ancient aliens. The object is made of a polished mineral, is tetrahedral in shape, and is surrounded by a spherical forcefield. The narrator speculates at one point that the mysterious aliens who left this structure on the Moon may have used mechanisms belonging "to a technology that lies beyond our horizons, perhaps to the technology of para-physical forces."

The narrator speculates that for millions of years (evidenced by dust buildup around its forcefield) the artifact has been transmitting signals into deep space, but it ceases to transmit when, sometime later, it is destroyed "with the savage might of atomic power". The narrator hypothesizes that this "sentinel" was left on the Moon as a "warning beacon" for possible intelligent and spacefaring species that might develop on Earth.

In 2001: A Space Odyssey, the operation of the sentinel is activated when sunlight touches it for the first time after it is dug up.

Algis Budrys found "The Sentinel" to be infuriating, saying that "one can raise a formidable reputation for profundity by repeating, over and over again, that the universe is wide and man is very small ... while our instruments show that the universe is wide, they are our instruments and we managed somehow to build them. There is no evidence whatsoever that Man is that goddamned small".[1]

The story was adapted and expanded upon in the 1968 film, 2001: A Space Odyssey, made by filmmaker Stanley Kubrick. Kubrick and Clarke modified and fused the story with other ideas. Clarke expressed impatience with its common description as the story on which the novel and movie are based. He explained

I am continually annoyed by careless references to "The Sentinel" as "the story on which 2001 is based"; it bears about as much relation to the movie as an acorn to the resultant full-grown oak. (Considerably less, in fact, because ideas from several other stories were also incorporated.) Even the elements that Stanley Kubrick and I did actually use were considerably modified. Thus the 'glittering, roughly pyramidal structure… set in the rock like a gigantic, many-faceted jewel' became—after several modifications—the famous black monolith. And the locale was moved from the Mare Crisium to the most spectacular of all lunar craters, Tycho—easily visible to the naked eye from Earth at Full Moon.[2]

The film was nominated for four Oscars, including Best Original Screenplay at the Oscars in 1969.

• "The Sentinel" title listing at the Internet Speculative Fiction Database
• "Sentinel of Eternity" at the Internet Archive