How many years is 1 second on the cosmic calendar?

About 438 years. Spread 13.8 billion years over the 31,536,000 seconds of a year and each second is 13.8 billion ÷ 31,536,000 ≈ 438 years. An 80-year human life takes 0.18 seconds.

How long is a cosmic day?

About 37.8 million years. One hour is about 1.58 million years, one minute about 26.3 thousand years, and an average month about 1.15 billion years.

When do humans appear on the cosmic calendar?

Sahelanthropus, one of the earliest known hominins (about 7 million years ago), sits at Dec 31 19:33:23. The Homo sapiens fossils from Jebel Irhoud, Morocco (about 315,000 years ago) sit at Dec 31 23:48:00. Cuneiform writing (about 3200 BCE) arrives at Dec 31 23:59:48.05, roughly 12 seconds before midnight.

Who invented the cosmic calendar?

Carl Sagan, in The Dragons of Eden (1977), using a universe age of 15 billion years. It appeared in the TV series Cosmos (1980) and Cosmos: A Spacetime Odyssey (2014). This page uses 13.8 billion years.

Is the cosmic calendar accurate?

The scale is exact; the error is in the dates. Planck (2018) measured the universe's age as 13.787 ± 0.020 billion years, and ±20 million years is ±13 hours on the calendar. Rounding 13.787 up to 13.8 billion moves the birth of the Solar System by only about 2.7 hours. Geological dates are more contested: 3.7-billion-year-old "stromatolites" from Isua, Greenland (Nutman et al. 2016) were challenged by Allwood et al. in 2018, and 3.7 versus 3.5 billion years is 5.3 days apart on the calendar.

Cosmic Calendar Calculator

Squeeze 13.8 billion years into one year: the Big Bang is at midnight on January 1, and now is midnight at the end of December 31. Enter a year and see which day and second it lands on.

Carl Sagan introduced the cosmic calendar in The Dragons of Eden (1977), using a universe age of 15 billion years. This page uses 13.8 billion: the Planck satellite's 2018 result is 13.787 ± 0.020 billion years. Every conversion runs in your browser.

1 calendar second: 438 years
1 minute: 26.3 thousand years
1 hour: 1.58 million years
1 day: 37.8 million years
1 month (average): 1.15 billion years

Today on the cosmic calendar

Working it out from your local date…

Converter

Year

On the cosmic calendar

Dec 31 23:59:59.86

0.13 seconds before midnight (now)

In the Civilization era

Nearest earlier event: Apollo 11 lands on the Moon (Dec 31 23:59:59.86)

The 12-month timeline

41 events in cosmic calendar order. Each date comes from the paper or institution listed with it.

Printing keeps only the scale and the timeline, on one A4 page.

January13.8 billion to 12.6 billion years ago

Jan 1 00:00:00The Big Bang13.8 billion years ago · Planck 2018 (A&A 641, A6)
Jan 1 00:14:28First atoms form and the universe turns transparent (the cosmic microwave background we see today)380 thousand years after the Big Bang · Penzias & Wilson 1965 (ApJ 142)
Jan 4 23:13:02The first stars switch on (theoretical estimate)150 million years after the Big Bang · Bromm & Larson 2004 (ARA&A 42)
Jan 8 16:05:13JADES-GS-z14-0, an early galaxy confirmed by JWST (redshift 14.32)290 million years after the Big Bang · Carniani et al. 2024 (Nature 633)
Jan 22 03:49:33The Milky Way's thick disk starts to form800 million years after the Big Bang · Xiang & Rix 2022 (Nature 603)

February12.6 billion to 11.6 billion years ago

Galaxies keep merging and growing this month; no single event is listed.

March11.6 billion to 10.4 billion years ago

Mar 10 18:26:05Kepler-444 and its five planets form, one of the oldest known planetary systems11.2 billion years ago · Campante et al. 2015 (ApJ 799)
Mar 29 06:46:57Peak star formation across the universe (redshift about 2)10.5 billion years ago · Madau & Dickinson 2014 (ARA&A 52)

April10.4 billion to 9.26 billion years ago

Apr 11 12:10:26The Milky Way swallows the dwarf galaxy Gaia-Enceladus10 billion years ago · Helmi et al. 2018 (Nature 563)

May9.26 billion to 8.09 billion years ago

Galaxies keep merging and growing this month; no single event is listed.

June8.09 billion to 6.96 billion years ago

Jun 3 09:44:20The Milky Way's thin disk starts to form; the Sun is later born in it8 billion years ago · Xiang & Rix 2022 (Nature 603)

July6.96 billion to 5.78 billion years ago

Jul 26 07:18:15Dark energy takes over and cosmic expansion switches from slowing down to speeding up6 billion years ago · Riess et al. 1998; Perlmutter et al. 1999

August5.78 billion to 4.61 billion years ago

Galaxies keep merging and growing this month; no single event is listed.

September4.61 billion to 3.48 billion years ago

Sep 2 04:56:52The first solids condense: the Solar System is born4.57 billion years ago · Connelly et al. 2012 (Science 338)
Sep 3 17:07:49The Moon forms after a giant impact4.51 billion years ago · Barboni et al. 2017 (Science Advances 3)
Sep 6 14:57:23Oldest known mineral on Earth: a zircon from Jack Hills, Australia4.4 billion years ago · Wilde et al. 2001 (Nature 409)

October3.48 billion to 2.31 billion years ago

Oct 2 06:41:44Stromatolites in Pilbara, Australia: early evidence of life3.43 billion years ago · Allwood et al. 2006 (Nature 441)
Oct 31 15:18:15Great Oxidation Event: oxygen starts building up in the air2.32 billion years ago · Bekker et al. 2004 (Nature 427)

November2.31 billion to 1.17 billion years ago

Nov 20 17:44:20Decimetre-sized multicellular eukaryote fossils, Gaoyuzhuang Formation, China1.56 billion years ago · Zhu et al. 2016 (Nature Communications 7)

December1.17 billion to 0 years ago

Dec 4 07:22:57Earliest known sexual reproduction: the red alga Bangiomorpha1.05 billion years ago · Gibson et al. 2018 (Geology 46)
Dec 13 11:39:07Snowball Earth700 million years ago
Dec 17 17:58:44The Cambrian begins and most animal phyla appear539 million years ago · ICS Chronostratigraphic Chart 2023
Dec 19 13:39:07Plants reach land (earliest land-plant spores, Argentina)470 million years ago · Rubinstein et al. 2010 (New Phytologist 188)
Dec 20 05:31:18Late Ordovician extinction445 million years ago
Dec 22 01:57:23Tiktaalik, a fish with wrists, between fish and four-legged animals375 million years ago · Daeschler, Shubin & Jenkins 2006 (Nature 440)
Dec 22 03:51:39Late Devonian extinction372 million years ago
Dec 25 08:02:05End-Permian extinction252 million years ago
Dec 25 21:21:54Eoraptor, one of the earliest dinosaurs231 million years ago · Sereno et al. 1993 (Nature 361)
Dec 26 16:24:31End-Triassic extinction201 million years ago
Dec 28 16:39:07Archaefructus, an early flowering plant from Liaoning, China125 million years ago · Sun et al. 2002 (Science 296)
Dec 30 06:06:15End-Cretaceous extinction66 million years ago
Dec 31 19:33:23Sahelanthropus, one of the earliest known hominins7 million years ago · Brunet et al. 2002 (Nature 418)
Dec 31 21:54:18Lomekwi 3 stone tools, Kenya, the oldest known3.3 million years ago · Harmand et al. 2015 (Nature 521)
Dec 31 21:58:07Lucy the Australopithecus lives3.2 million years ago · Johanson & Taieb 1976 (Nature 260)
Dec 31 23:48:00Homo sapiens fossils at Jebel Irhoud, Morocco315 thousand years ago · Hublin et al. 2017 (Nature 546)
Dec 31 23:58:02Cave painting in Sulawesi, Indonesia, the oldest known narrative art51.2 thousand years ago · Oktaviana et al. 2024 (Nature 631)
Dec 31 23:59:32.57Farming begins in the Fertile Crescent: wheat and barley12 thousand years ago · Zohary, Hopf & Weiss 2012
Dec 31 23:59:48.05Cuneiform writing appears at Uruk3200 BCE · Uruk IV tablets
Dec 31 23:59:49.52The Great Pyramid of Khufu is built2560 BCE · Lehner & Hawass 2017
Dec 31 23:59:55.37Year 1 CE1 CE
Dec 31 23:59:58.89Copernicus publishes De revolutionibus1543 CE · De revolutionibus
Dec 31 23:59:59.04Galileo publishes Sidereus Nuncius, reporting four moons of Jupiter1610 CE · Sidereus Nuncius
Dec 31 23:59:59.22Newton publishes the Principia1687 CE · Principia
Dec 31 23:59:59.86Apollo 11 lands on the Moon1969 CE · NASA

FAQ

How many years is 1 second on the cosmic calendar?: About 438 years. Spread 13.8 billion years over the 31,536,000 seconds of a year and each second is 13.8 billion ÷ 31,536,000 ≈ 438 years. An 80-year human life takes 0.18 seconds.
How long is a cosmic day?: About 37.8 million years. One hour is about 1.58 million years, one minute about 26.3 thousand years, and an average month about 1.15 billion years.
When do humans appear on the cosmic calendar?: Sahelanthropus, one of the earliest known hominins (about 7 million years ago), sits at Dec 31 19:33:23. The Homo sapiens fossils from Jebel Irhoud, Morocco (about 315,000 years ago) sit at Dec 31 23:48:00. Cuneiform writing (about 3200 BCE) arrives at Dec 31 23:59:48.05, roughly 12 seconds before midnight.
Who invented the cosmic calendar?: Carl Sagan, in The Dragons of Eden (1977), using a universe age of 15 billion years. It appeared in the TV series Cosmos (1980) and Cosmos: A Spacetime Odyssey (2014). This page uses 13.8 billion years.
Is the cosmic calendar accurate?: The scale is exact; the error is in the dates. Planck (2018) measured the universe's age as 13.787 ± 0.020 billion years, and ±20 million years is ±13 hours on the calendar. Rounding 13.787 up to 13.8 billion moves the birth of the Solar System by only about 2.7 hours. Geological dates are more contested: 3.7-billion-year-old "stromatolites" from Isua, Greenland (Nutman et al. 2016) were challenged by Allwood et al. in 2018, and 3.7 versus 3.5 billion years is 5.3 days apart on the calendar.