It’s hard to pick, but I think my favourite is what I have on my computer desktop:
It’s a picture of the ‘star’ at the bottom of Orion’s sword in the constellation Orion. It’s not actually a star, but a nebula – a cloud of gas and dust where new stars are forming right now. You can see the little baby stars in the middle…
I love it because it shows that things in the universe are still forming, and that the universe is dynamic, and always changing, and that we can learn things about our past, and our future, just by looking into the sky!
It’s the only picture that anywhere near manages to capture the sheet enormity of the universe.
They made it by point Hubble at a patch of sky about 1cm across, a patch of sky they deliberately chose because it was really really empty. They left Hubble looking at this one place for about a month, taking a really long exposure picture.
The Hubble deep field is what it saw.
In that 1cm patch of empty, there are hundreds and hundreds of galaxies. Each one of the points on that picture (except a couple) is a galaxy that contains billions and billions of stars.
So imagine if we spread that picture across the whole sky. That’s billions of these galaxies. Billions and billions and billions, looking back in time through 13.7 billion years.
And if we took a longer picture with a better telescope (Imagine what the James Webb Deep field would look like!) we would see even more.
That makes the universe seem sooooo big, and us so small, but like Neil Tyson says – we’re part of that universe. We’re made of the same stuff those stars are.