The garden
Living documents we keep tending, revising, and growing.
5 documents
Two stars, one bright and one faint, and no way to tell near from far by looking. How astronomers built a chain of rulers from a thumb's-width of parallax to exploding stars — and where the chain has started to crack.
It has 'year' in the name, so it sounds like a span of time. It's a distance — and the reason astronomers measure the sky this way is the most poetic fact in the science.
The Big Bang made hydrogen, helium, and almost nothing else. Every heavier atom in your body — the carbon, the calcium, the iron, the gold — was built later, inside stars and the violence of their deaths.
Galaxies spin too fast to hold together with the matter we can see. Either there's a vast amount of invisible stuff, or gravity itself is wrong. A notebook on the leading suspects.
Distant galaxies rush away from us, and the farther they are the faster they go — not because we're special, but because space itself is stretching. What that does and doesn't mean.