Each galaxy lives within its own three-dimensional halo of dark matter whose gravitational field corrals the stars within it. Without the stars, the halo would still be there, albeit invisible to our eyes; but if the halo vanished, the stars would scatter into the depths of the universe – just as a Christmas tree remains a tree with or without the pretty lights. Whereas without the tree, the lights would merely be a puddle of colour on the snowy ground.
Imagine living in a world where walking and biking was as safe – by Commander Hadfield's measure – as flying in space.
This is the week the Nobel Prizes are announced, and today is the day (at least in New Zealand; first place in the world to see the light, as the tourist people say) the Physics prize is announced. And this year the odds-on favourite will be LIGO and the discovery of gravitational waves.
NASA has an undoubted ability to sell a story, and it has been making the most of the anthropomorphic appeal of this brave little $3 billion, 5 ton, plutonium-powered spacecraft on its two-decade mission. But the hype is not misplaced: Saturn has a key place in the evolving human understanding of the cosmos.
As you can guess from the title, The First Three Minutes tells the story of the moments following the Big Bang. The early universe sets the stage for the development of the cosmos we observe today, and the Cosmic Microwave Background is a key link between the distant past and the present day.