Cosmic Calendar
Carl Sagan squeezed all 13.8 billion years of cosmic history into a single year. On this calendar the Big Bang is January 1st and right now is the last second of December 31st — see where every great event falls.
Imagine all 13.8 billion years of cosmic time squeezed into one calendar year. Here is how much real time each tick represents:
The year of the universe
January
The Big Bang
January 1The universe begins — space, time, and energy burst into existence.
First stars
January 6The first stars ignite and start forging heavier elements.
The Milky Way forms
January 6Our home galaxy begins to take shape from primordial gas.
First galaxies
January 11Gravity gathers stars into the earliest galaxies.
September
The Solar System forms
September 2A cloud of gas and dust collapses into the Sun and planets.
Earth forms
September 2Our planet coalesces from the debris orbiting the young Sun.
First life on Earth
September 22The earliest single-celled microbes appear in the oceans.
October
Photosynthesis begins
October 3Cyanobacteria start releasing oxygen, slowly changing the air.
November
Complex cells
November 9Cells with a nucleus (eukaryotes) evolve, a leap toward complex life.
December
Everything you call "history" happens in the final hours of December 31st.
Multicellular life
December 5Cells join together to form the first multicellular organisms.
Cambrian explosion
December 17Animal life diversifies rapidly into most major body plans.
Plants colonize land
December 19The first plants spread across the continents.
Dinosaurs appear
December 25Dinosaurs rise and come to dominate life on land.
Dinosaurs die out
December 30An asteroid impact triggers a mass extinction, ending the dinosaurs.
First primates
December 30The earliest primates, our distant ancestors, appear.
Genus Homo
December 3122:24:46The first members of our own genus, Homo, begin making stone tools.
Modern humans
December 3123:48:34Homo sapiens — anatomically modern humans — emerge in Africa.
Farming begins
December 3123:59:32Humans start cultivating crops and settling into villages.
Writing invented
December 3123:59:47The first writing systems are created, beginning recorded history.
Your life on the cosmic calendar
Enter your age to see how little of the cosmic year your whole life takes up.
What is the Cosmic Calendar?
The Cosmic Calendar is a way to visualize the history of the universe popularized by Carl Sagan, in which the 13.8 billion years since the Big Bang are scaled down to a single year. On this scale one second is about 438 years and one day is about 38 million years. The Solar System forms in early September, the first life in late September, and all of recorded human history fits into the last few seconds before midnight on December 31st.
Frequently asked questions
Who invented the Cosmic Calendar?
Astronomer Carl Sagan popularized it in his 1977 book "The Dragons of Eden" and his television series "Cosmos," as a way to make the vast scale of cosmic time understandable.
How long is one cosmic second?
Because 13.8 billion years are compressed into 365 days, one second of the cosmic calendar equals about 438 real years, and one day equals about 38 million years.
When did humans appear on the calendar?
Anatomically modern humans (Homo sapiens) appear only in the last few minutes of December 31st, and all of written history occupies just the final 10 to 15 seconds.
Why is the year 365 days with no leap day?
Sagan used a simple 365-day year so the mapping stays clean: January 1st is the Big Bang and the final instant of December 31st is the present moment.
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