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05 · Science Library

Time, numbers and the sky.

Calendars of the world, numeral systems, astronomy, the Solar System and the universe.

Sources in every card · References

The sky of today · the NEO day

01The three days

One day, three ways to tell it.

The Maya Tzolkʼin and the Mexica Tonalpohualli count 260 days with 13 numbers and 20 signs; the NEO day follows the Earth on its orbit and the Moon in its phase. Choose any day.

02Today in every count

The same day in thirteen counts of humanity.

Unicode CLDR calendars and the Maya and Mexica counts with the GMT correlation (584283), computed in your browser. Nothing is sent anywhere. The day chosen above changes them all.

  • Gregorian…Solar · the civil calendar of the world
  • Hijri…Lunar · Islamic calendar
  • Hebrew…Lunisolar · Jewish calendar
  • Chinese…Lunisolar · year of the cycle of sixty
  • Persian…Solar · Solar Hijri, Iran and Afghanistan
  • Indian national…Solar · Saka era
  • Ethiopian…Solar · thirteen months
  • Buddhist…Solar · Buddhist era, Thailand
  • Japanese…Era names · Reiwa
  • Maya Long Count…Days since the creation, 13.0.0.0.0
  • Maya Tzolkʼin · Haabʼ…260 days · 365 days
  • Mexica Tonalpohualli…260 days: 13 numbers × 20 signs
  • The Moon…Phase of the day

03The Earth right now

Where the Sun shines, this minute.

The point where the Sun stands overhead and the line between day and night, from the position of the Sun computed in your browser and redrawn every minute.

Great sitesNatural wondersNight

04Solar System

One star, eight planets, one home.

The bodies of our sky, with the symbols that astronomy has used for centuries.

Star

Sun

Our star

A 4.6-billion-year-old star holding 99.8% of the Solar System's mass.

Ask the librarian

Planet

Mercury

The swift messenger

The closest planet to the Sun; a year of 88 days.

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Planet

Venus

The morning and evening star

The hottest planet, wrapped in clouds; Mesoamerica tracked its 584-day cycle.

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Planet

Earth

Our home

The only world known to hold life; one ocean, one atmosphere, one bioregion.

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Moon

Moon

Earth's companion

Its 29.5-day cycle gave many peoples their months.

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Planet

Mars

The red planet

Iron-red deserts and the tallest volcano in the Solar System.

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Planet

Jupiter

The giant

The largest planet; its storm, the Great Red Spot, is larger than Earth.

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Planet

Saturn

The ringed planet

Rings of ice and rock; a year of 29.5 Earth years.

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Planet

Neptune

The far blue world

The farthest planet, found by mathematics in 1846.

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05Numerals of the World

Ten ways to write a number.

Base 10, base 20, base 60: how humanity learned to count, from Babylon to the Maya. The Maya numbers 0–19 →

Base 10

Hindu-Arabic

Base 10 · India → the world

Born in India with zero, carried by Arab scholars; today the numerals of the world.

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Base 20

Maya

Dots and bars

A shell for zero, dots of one, bars of five — counted in twenties. Three bars: fifteen.

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Base 60

Babylonian

Wedges of clay

Wedges for one (▼) and ten (◀); our 60 minutes and 360 degrees come from Mesopotamia.

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Base 10

Chinese

Characters

Written with characters; counting rods anticipated place value.

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Base 10

Devanagari

Numerals of India

The family from which the world's digits descend.

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Base 10

Egyptian

Hieroglyphs

Strokes for 1, heel bones (∩) for 10, coils of rope for 100: ∩|| is twelve.

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Alphabetic

Greek

Letters as numbers

Each letter also a number: α = 1, β = 2, γ = 3.

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Base 10

Arabic-Indic

Eastern Arabic

Used today across much of the Arab world.

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06Words of science

The terms of the library.

Every concept is a term, connected, in every language, with its sources.

Calendar
A count of time tied to the Sun, the Moon, the stars or sacred numbers.
Numeral system
A way of writing numbers: base 10, base 20 (Maya), base 60 (Babylon).
Tzolk'in
The sacred count of 260 days: 20 day-signs combined with 13 numbers.
Tonalpohualli
The count of days: 260 days made of 20 day-signs and 13 numbers.
Long Count
A count of days in a modified base 20 (a tun of 18 × 20 days) from the era date 13.0.0.0.0, 11 August 3114 BCE, used for historical dates.
NEOLEDGE
The knowledge NEO shares, generates, organizes and spreads: every concept a term, connected, in every language, with its sources.

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