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Scientists detect distant planets by measuring the color shifts marking the slow wobble in the precession of stars. The unseen planet's gravity pulling on the star. The amount of wobble infers the size of the planet orbiting it, with everyone hoping for a roughly earth sized planet in the "hospitable zone" to make headlines and add to the list places where life may exist. The point is looking at the blacked-out-except-for-cities's-dots atlas pages is analogy to the stars-which-may-harbor-life. You look at them and imagine worlds.
Like Lutz Bacher's interest in the granular, or Paul Thek's dust, or Gonzalez-Torres' replenishing feilds, it converts the world into an expanse, appending distance, we feel distant, its loss, its dissolve, things returning to dust.
See too: Lutz Bacher at 356 Mission