The Cosmic Calendar
Shrink the universe's 13.8 billion years into one calendar year and the Big Bang is New Year's midnight, the dinosaurs die on 30 December, and all of history fits in the final seconds.
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- Most recent milestone—
- Next milestone on the cosmic calendar—
13.8 billion years squeezed into one year
Carl Sagan introduced the Cosmic Calendar in his 1977 book The Dragons of Eden and made it famous in the 1980 TV series Cosmos; Neil deGrasse Tyson revived it in the 2014 series. The idea: shrink the whole history of the universe into one calendar year. The Big Bang happens at the first instant of 1 January. Now is the stroke of midnight on 31 December.
This version uses the current Planck age of 13.787 billion years and up-to-date dates for each event, so it differs a little from the versions in books and on TV.
| One cosmic… | equals |
|---|---|
| Year | 13.787 billion years |
| Month | ≈ 1.15 billion years |
| Day | ≈ 37.8 million years |
| Hour | ≈ 1.57 million years |
| Minute | ≈ 26,200 years |
| Second | ≈ 437 years |
The year at a glance
January
- 1 Big Bang
- 1 Light breaks free — the cosmic microwave background
- 5 First stars ignite
- 8 Earliest galaxies seen by JWST
- 27 Reionization ends — the universe turns transparent to ultraviolet light
February
Galaxies form, stars live and die — nothing on Earth yet.
March
- 15 Milky Way swallows the Gaia-Enceladus galaxy
April
Galaxies form, stars live and die — nothing on Earth yet.
May
- 13 The Milky Way's thin disk takes shape
June
Galaxies form, stars live and die — nothing on Earth yet.
July
Galaxies form, stars live and die — nothing on Earth yet.
August
Galaxies form, stars live and die — nothing on Earth yet.
September
- 2 The Sun and Solar System form
- 2 Earth forms
- 3 Moon forms after a giant impact
- 6 Oldest known Earth minerals (Jack Hills zircons)
- 25 Earliest widely accepted traces of life
October
- 29 Great Oxidation Event — oxygen builds up in the air
November
- 14 Complex (eukaryotic) cells appear
December
- 15 Ediacaran animals — first large multicellular life
- 17 Cambrian explosion
- 19 Plants colonise land
- 22 Four-limbed animals walk onto land
- 25 Great Dying — worst mass extinction
- 25 First dinosaurs
- 26 First mammal-like animals (mammaliaforms)
- 28 Flowers bloom
- 30 Asteroid ends the age of dinosaurs
31 December: see below.
For eight and a half months there is no Sun at all. The Solar System doesn't form until the start of September, and life — single cells only — fills the autumn. Animals you could see without a microscope don't appear until mid-December.
31 December, hour by hour
| Cosmic time on 31 Dec | Event | Real date |
|---|---|---|
| 19:33:08 | Human and chimpanzee lineages split | 7.0 million years ago |
| 22:20:52 | First stone tools (and the genus Homo) | 2.6 million years ago |
| 23:48:33 | Homo sapiens appears | 300,000 years ago |
| 23:59:32 — 27.4 s before midnight | Farming begins | 12,000 years ago |
| 23:59:48 — 11.9 s before midnight | Writing is invented | 5,200 years ago |
| 23:59:55 — 4.7 s before midnight | The Julian calendar starts (45 BCE) | 2,070 years ago |
| 23:59:58 — 1.0 s before midnight | The Gregorian calendar is introduced (1582) | 444 years ago |
| 23:59:59 — 0.1 s before midnight | Humans walk on the Moon (1969) | 57 years ago |
| 24:00:00 (midnight) | Now — midnight, 31 December | Today |
All of recorded history — writing, the pyramids, every empire, every calendar ever made — happens in the last 12 seconds of the year. The Gregorian calendar you are reading this page in arrives about one second before midnight.
Every event, with its cosmic date
| Event | Cosmic date | Real date | Note |
|---|---|---|---|
| Big Bang | 1 January, 00:00:00 | 13.787 billion years ago | Planck 2018 age: 13.787 ± 0.020 billion years. |
| Light breaks free — the cosmic microwave background | 1 January, 00:15:14 | 13.787 billion years ago | About 380,000 years after the Big Bang. |
| First stars ignite | 5 January | 13.600 billion years ago | Roughly 100–250 million years after the Big Bang; not yet observed directly. |
| Earliest galaxies seen by JWST | 8 January | 13.500 billion years ago | Galaxies at redshift 14 shine from under 300 million years after the Big Bang. |
| Reionization ends — the universe turns transparent to ultraviolet light | 27 January | 12.800 billion years ago | Complete by roughly 1 billion years after the Big Bang. |
| Milky Way swallows the Gaia-Enceladus galaxy | 15 March | 11.000 billion years ago | Estimates range from about 8 to 11 billion years ago. |
| The Milky Way's thin disk takes shape | 13 May | 8.80 billion years ago | Oldest thin-disk stars are about 8–9 billion years old. |
| The Sun and Solar System form | 2 September | 4.57 billion years ago | From calcium-aluminium-rich inclusions in meteorites. |
| Earth forms | 2 September | 4.54 billion years ago | ± about 50 million years. |
| Moon forms after a giant impact | 3 September | 4.50 billion years ago | Leading hypothesis; timing 4.4–4.5 billion years ago. |
| Oldest known Earth minerals (Jack Hills zircons) | 6 September | 4.40 billion years ago | Western Australia. |
| Earliest widely accepted traces of life | 25 September | 3.70 billion years ago | Some claims go back to 4.1 billion years and are debated. |
| Great Oxidation Event — oxygen builds up in the air | 29 October | 2.40 billion years ago | Cyanobacteria change the planet's chemistry. |
| Complex (eukaryotic) cells appear | 14 November | 1.80 billion years ago | Estimates range from about 1.6 to 2.1 billion years ago. |
| Ediacaran animals — first large multicellular life | 15 December | 635 million years ago | Start of the Ediacaran period. |
| Cambrian explosion | 17 December | 538 million years ago | Most animal body plans appear in the fossil record. |
| Plants colonise land | 19 December | 470 million years ago | — |
| Four-limbed animals walk onto land | 22 December | 375 million years ago | Tiktaalik-era transition. |
| Great Dying — worst mass extinction | 25 December | 252 million years ago | End-Permian; about 90% of marine species lost. |
| First dinosaurs | 25 December | 233 million years ago | Late Triassic. |
| First mammal-like animals (mammaliaforms) | 26 December | 225 million years ago | — |
| Flowers bloom | 28 December | 130 million years ago | Earliest flowering plants. |
| Asteroid ends the age of dinosaurs | 30 December, 06:03:53 | 66 million years ago | Chicxulub impact. |
| Human and chimpanzee lineages split | 31 December, 19:33:08 | 7.0 million years ago | About 6–7 million years ago. |
| First stone tools (and the genus Homo) | 31 December, 22:20:52 | 2.6 million years ago | — |
| Homo sapiens appears | 31 December, 23:48:33 | 300,000 years ago | Jebel Irhoud fossils, Morocco. |
| Farming begins | 31 December, 23:59:32 | 12,000 years ago | Fertile Crescent and elsewhere. |
| Writing is invented | 31 December, 23:59:48 | 5,200 years ago | Mesopotamia, about 3200 BCE. |
| The Julian calendar starts (45 BCE) | 31 December, 23:59:55 | 2,070 years ago | Ancestor of today's calendar. |
| The Gregorian calendar is introduced (1582) | 31 December, 23:59:58 | 444 years ago | — |
| Humans walk on the Moon (1969) | 31 December, 23:59:59 | 57 years ago | — |
| Now — midnight, 31 December | 31 December, 24:00:00 | Today | — |
Your life on the Cosmic Calendar
Frequently asked questions
What is the Cosmic Calendar?
A way of picturing the 13.8-billion-year history of the universe as a single calendar year, with the Big Bang at midnight on 1 January and the present at midnight on 31 December. Carl Sagan popularised it in 1977.
When do humans appear on the Cosmic Calendar?
Homo sapiens appears at about 11:48 p.m. on 31 December — only 11 and a half cosmic minutes before midnight. All of recorded history fills the last 12 seconds.
How long is one second on the Cosmic Calendar?
About 437 years. One cosmic day is about 37.8 million years.
When did the Sun form on the Cosmic Calendar?
Around 1–2 September, about 4.57 billion years ago.