The Cosmic Calendar is a method to visualize the chronology of the universe, scaling its currently understood age of 13.787 billion years to a single

year A year is a unit of time based on how long it takes the Earth to orbit the Sun. In scientific use, the tropical year (approximately 365 Synodic day, solar days, 5 hours, 48 minutes, 45 seconds) and the sidereal year (about 20 minutes longer) ...

in order to help intuit it for pedagogical purposes in

science education Science education is the teaching and learning of science to school children, college students, or adults within the general public. The field of science education includes work in science content, science process (the scientific method), some ...

popular science Popular science (also called pop-science or popsci) is an interpretation of science intended for a general audience. While science journalism focuses on recent scientific developments, popular science is more broad ranging. It may be written ...

. A similar analogy used to visualize the

geologic time scale The geologic time scale or geological time scale (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochro ...

and the history of life on Earth is the Geologic Calendar. In this visualization, the

Big Bang The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models based on the Big Bang concept explain a broad range of phenomena, including th ...

took place at the beginning of January 1 at midnight, and the current moment maps onto the end of December 31 just before midnight. At this scale, there are 438 years per cosmic second, 1.58 million years per cosmic hour, and 37.8 million years per cosmic day. The

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

materialized in Cosmic September. The

Phanerozoic The Phanerozoic is the current and the latest of the four eon (geology), geologic eons in the Earth's geologic time scale, covering the time period from 538.8 million years ago to the present. It is the eon during which abundant animal and ...

corresponds only to the latter half of December, with the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

only happening on the penultimate day on the Calendar. The

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS), as well as the current and most recent of the twelve periods of the ...

only applies to the last four hours on the final Cosmic Day, with the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

only applying to the final 23 Cosmic Seconds. On the other hand, relic radiation is dated at the first fifteen minutes of the very first Cosmic Day; even if we stretch the Cosmic Calendar to 100 years, the relic radiation would still happen just after the start of the second Cosmic Day. The concept was popularized by

Carl Sagan Carl Edward Sagan (; ; November 9, 1934December 20, 1996) was an American astronomer, planetary scientist and science communicator. His best known scientific contribution is his research on the possibility of extraterrestrial life, including e ...

in his 1977 book '' The Dragons of Eden'' and on his 1980 television series ''

Cosmos The cosmos (, ; ) is an alternative name for the universe or its nature or order. Usage of the word ''cosmos'' implies viewing the universe as a complex and orderly system or entity. The cosmos is studied in cosmologya broad discipline covering ...

''. Sagan goes on to extend the comparison in terms of surface area, explaining that if the Cosmic Calendar were scaled to the size of a football field, then "all of human history would occupy an area the size of ishand". The Cosmic Calendar was reused in the 2014 series, '' Cosmos: A Spacetime Odyssey''.

Cosmology

Sources Date in year calculated from formula T(days) = 365 days * ( 1- T_Gya/13.787)

Evolution of life on Earth

Human evolution

History begins

References

{{Portal bar, History, Astronomy, Stars, Spaceflight, Outer space, Solar System, Science Units of time

Calendar A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A calendar date, date is the designation of a single and specific day within such a system. A calendar is ...

Time in astronomy Popular science Carl Sagan Scientific visualization Analogy