4 ideas
Peter Nilson, working at Uppsala Observatory, compiled the Uppsala General Catalogue of Galaxies (1973), a systematic record of about 13,000 galaxies measured and classified from survey photographic plates. His career is a concrete case of years of patient, quantitative sky-cataloguing later becoming the raw material for literary meditation on the scale and ending of things.
Light travels at a finite speed, so everything seen in the sky is seen as it was when the light left it. A distant galaxy is seen as it was millions or billions of years ago, not as it is now. The night sky is therefore not a single present moment but layers of different pasts arriving together, and to look further out is to look further back.
Measured against cosmological time, spanning billions of years and extending into a far future of dying stars, all of human history is a vanishingly thin slice. Taking that scale seriously dissolves the assumption that the present, or humanity itself, is central or permanent. The same scale can also make a brief, conscious existence seem more precious rather than meaningless.
Stars exhaust their fuel, fewer new ones form, and usable energy spreads out until nothing can do work. This is the thermodynamic end state known as heat death. On that view, every structure is a temporary pattern living off an energy gradient that will eventually run out, so the far future holds an end for the cosmos as well as for civilizations.