Galaxies Explained (v2 cinematic)

On a really dark night — far from any city light — there is sometimes a faint white smear across the sky. People have always called it the Milky Way. [pause:700] Here is the wild part. That smear is OUR galaxy. Seen from inside. Edge-on. [pause:600] We aren't looking AT it. We are looking THROUGH it. Every star you can see with your naked eye is a neighbour, inside our same galaxy.

So what IS a galaxy, really? [pause:500] A huge family of stars. Two hundred billion of them, in ours. All held together by gravity. All slowly turning, like a giant pinwheel. [pause:700] Pull the camera back from our sun. The sun shrinks. To a dot. To one dot in a sea of dots. [pause:500] Until the shape of the place we live in finally comes into view.

And it is enormous. [pause:500] One hundred thousand light-years across. [pause:400] Light is the fastest thing in the universe — and it still needs one hundred thousand years just to cross from one edge of our galaxy to the other. [pause:700] Our sun rides around the centre of it once every two hundred and thirty million years. [pause:500] The last time we were here in our orbit — dinosaurs were still around.

Not every galaxy looks like ours. There are three main shapes. [pause:500] Spirals — wheels with curving arms. That is us. That is Andromeda. [pause:400] Ellipticals — smooth, footballs of mostly old stars. [pause:400] And irregulars — clumpy, lopsided things. Usually because two galaxies smashed together and pulled each other apart.

Take a tour. Step through some of the most famous galaxies we know about — Andromeda, the Sombrero, the Whirlpool, all of them. [pause:500] When you are done, switch on the collision view, and drag the time slider. You will watch the Milky Way and Andromeda fall toward each other over billions of years, swing past each other, and finally merge — into one giant elliptical galaxy. [pause:500] That actually IS going to happen.

And here is the next zoom-out. [pause:500] Our galaxy isn't rare. There are about two TRILLION galaxies in the part of the universe we can see. [pause:600] They aren't scattered randomly. They clump. The Milky Way and Andromeda live in a little crowd of about fifty galaxies. Crowds gather into clusters. Clusters into superclusters. And superclusters form a tangled cosmic web that stretches across everything.

So here is the whole picture in three zooms. [pause:500] A star — one sun, like ours. [pause:400] A galaxy — about two hundred billion stars, like our Milky Way. [pause:400] A universe — about two trillion galaxies. [pause:700] You live on one planet, around one star, in one arm of one galaxy, in one corner of a universe of trillions. [pause:500] That is your address.