First look
The idea, in plain words
The universe is 13.8 billion years old. Nobody can picture a number like that, so here is a trick. Squeeze the whole of it into one calendar year, with the beginning at midnight as 1 January starts and this moment at midnight as 31 December ends. On that scale one day is about 38 million years, and one second is more than four centuries.
The very start is over almost before the year begins. The first elements are made in a tiny fraction of the first second. The glowing fog clears, and the oldest light sets out, 14 minutes after midnight on 1 January. This map shows that light as it arrives today.
Then nothing shines for days. The first stars light up around 6 January. By 22 January there are small young galaxies, and this real photograph shows some of them as they were then. Through the rest of the winter and the spring, galaxies grow and collide, and stars are born and die by the billion, each one making heavier elements and scattering them.
Two thirds of the year go by before there is a Sun. It forms, with the Earth and the other planets, on 1 September, from gas that earlier stars had already enriched. Everything solid on the Earth is made of what those stars left.
Life begins in the sea by about 22 September. For nearly all the time since, it stays small and simple. The dinosaurs are wiped out at about six in the morning on 30 December.
The last day is where we come in. Our own kind of human appears at about eleven minutes to midnight on 31 December. A long human life lasts less than a fifth of a second. Everything in every history book happened in the last few seconds before the bell.
Go deeper
That was the idea. The same subject is written again below for readers who want more, each on a page of its own.
Words used here
- Big Bang
- The hot, dense early state from which the universe has been expanding and cooling for 13.8 billion years.
- Cosmic microwave background
- The oldest light there is: a faint glow of microwaves coming from every direction in the sky.
- Dark ages
- The stretch of about 200 million years after the oldest light was released and before the first stars lit.
- Galaxy
- A huge family of stars, gas and dust held together by gravity.
- Star
- A ball of hot gas held together by its own gravity and shining by nuclear fusion in its core.
- Look-back time
- How long ago the light you are seeing set out.
- Power of ten
- A step of ten times bigger or ten times smaller, the only practical way to count the sizes of things in space.
Where this comes from
- NASA, Overview of the universe: cosmic history
- ESA, Planck and the cosmic microwave background
- ESA/Hubble, Hubble sees galaxies galore: the Ultra Deep Field (2004)
- Smithsonian National Museum of Natural History, Homo sapiens
- Renne and others 2013, Time scales of critical events around the Cretaceous-Paleogene boundary
The words are written for this site. The pictures are drawn by the page from the figures in the lesson, and each one says underneath what it is based on.