The Cosmic Calendar: The History of the Universe in One Year

The universe is about 13.8 billion years old. That number is so large it's almost meaningless: there's no way to feel the difference between a billion years and ten billion. So in the 1970s the astronomer Carl Sagan popularised a simple trick. Squeeze the whole history of the universe into a single calendar year, and suddenly the size of it becomes something you can grasp.

How the scale works

Put the Big Bang at the stroke of midnight on 1 January, and today at the stroke of midnight at the end of 31 December. We use the age measured by the Planck satellite, 13.787 billion years. On that scale:

  • one month is about 1.1 billion years
  • one day is about 37.8 million years
  • one hour is about 1.57 million years
  • one second is about 437 years

January to August: a universe without us

The first atoms form just 14 minutes into New Year's Day, when the universe has cooled enough for light to travel freely. The oldest galaxies the James Webb Space Telescope has found are already shining by 8 January. The thick disc of our own galaxy, the Milky Way, starts to form around 21 January, and star formation across the universe reaches its peak in early April.

Then comes a long stretch that feels empty on the calendar but isn't. Through the spring and summer, generation after generation of stars live and die, forging the carbon, oxygen and iron that will one day make up planets and people. By the end of August, our Sun still hasn't formed.

September: the Sun and Earth

The Sun and its planets finally form on 2 September, about 4.57 billion years ago. The earliest widely accepted evidence of life on Earth appears at the end of September, around 3.5 billion years ago. For most of the autumn, life is microscopic. Oxygen starts to build up in the air around 29 October.

December: almost everything you know

Nearly all the life we'd recognise is squeezed into the last month of the year.

  • 4 December: a red alga called Bangiomorpha, one of the earliest known multicellular organisms
  • 17 December: the Cambrian explosion, when most of the main groups of animals appear
  • 19 December: plants move onto land
  • 25 December: the Great Dying wipes out most life on Earth at around 8 in the morning, and the first dinosaurs appear that same evening
  • 30 December, about 6 am: an asteroid strikes what is now Mexico and ends the age of the dinosaurs

31 December: the last hours

The first members of our own genus, Homo, appear at about 22:13 on New Year's Eve. Homo sapiens, our own species, turns up at 23:48, just twelve minutes before midnight.

Then the zoom gets extreme. Farming begins at 23:59:32. Writing is invented at 23:59:48, which means that all of recorded history, every empire, every book, every name you've ever learned in school, fits into the last 11.4 seconds of the year. Year 1 of the Common Era falls at 23:59:55. Galileo first turns a telescope to the sky less than a second before midnight, and the Apollo astronauts walk on the Moon about a tenth of a second before the year ends.

Why it matters

The Cosmic Calendar isn't really about dates. It's about perspective. It shows how recently we arrived, how long the universe managed without us, and how much had to happen first: stars cooking up the atoms in your body, billions of years of microbes changing the air, and a lucky escape for small mammals on 30 December. It can make us feel very small, and also very lucky to be here at all.

A note on accuracy: every date here comes from dividing an event's age by the age of the universe, and most of those ages have uncertainties of a few per cent. So treat the times as a guide to scale, not a precise timetable.

Put it on your wall

We've drawn the whole year as a poster: twelve months, December day by day, and the last minute of 31 December enlarged so you can see history fit into it. The Cosmic Calendar art print comes in A3 and A2, or you can download it and print it at home.

Sources

Back to blog