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How We Know the Universe Is Expanding

3 sessions, in order

Starlight's barcode, the barcode slid toward red in every distant galaxy, and running that expansion backward to the Big Bang.

1.P&A-64The Sun's BarcodePhysics & Astronomy~25 minHow can anyone know what a star is made of without going there? Every element soaks up its own exact colours, so the gaps in split starlight read like a barcode.
2.P&A-65Every Galaxy Is Running AwayPhysics & Astronomy~25 minHow do we know the universe is expanding? The farther away a galaxy is, the faster it's moving off, and a stretched strip of elastic shows why that's what growing space looks like from anywhere.
3.P&A-45The Stretching BalloonPhysics & Astronomy~27 minIs the universe expanding into something? Why every galaxy is moving away from every other one, and what that means about how it all began.