The Whole Universe

Key facts

Hubble Ultra Deep Field

Astronomers pointed Hubble at a tiny, seemingly empty patch of sky and collected light for days. The image revealed about 10,000 galaxies – some seen as they were less than a billion years after the Big Bang.

The Big Bang & expanding universe

The universe began in an extremely hot, dense state about 13.8 billion years ago and has been expanding and cooling ever since. Galaxies are moving apart not because they fly through space, but because space between them is stretching.

Cosmic Microwave Background

The cosmic microwave background is the afterglow of the Big Bang: light released when the universe first became transparent, about 380,000 years after it began. It has been stretched by the expanding universe into faint microwaves that come from every direction.

Dark Matter & Dark Energy

Everything we can see – stars, planets, people – is only about 5% of the universe. The rest is dark matter, invisible stuff that pulls on galaxies with its gravity, and dark energy, which is making the expansion of the universe speed up. Nobody yet knows what either of them is.

Quiz

1. How old is the universe?

   • ☐ 6,000 years
   • ☐ 4.5 billion years
   • ☐ 13.8 billion years
   • ☐ It has always existed

2. Where did the Big Bang happen?

   • ☐ Near the Milky Way
   • ☐ At the centre of the universe
   • ☐ Everywhere at once
   • ☐ Inside a black hole

3. About how much of the universe is ordinary matter (atoms)?

   • ☐ About 5%
   • ☐ About 50%
   • ☐ About 95%
   • ☐ 100%

Find it in the sky

Use the Sky Finder at seethestar.com. Tick what you find and write when you saw it.