I can never look now at the Milky Way without wondering from which of those banked clouds of stars the emissaries are coming. If you will pardon so commonplace a simile, we have set off the fire alarm and have nothing to do but to wait.
I do not think we will have to wait for long
"The Sentinel" (1948), originally titled "Sentinel of Eternity" this is the short story which later provided the fundamental ideas for 2001: A Space Odyssey (1968) written by Clarke and Stanley Kubrick.