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Our world is a planet where human beings have formed many societies.

Nobody knows whether there are intelligent beings on other worlds. There are about one septillion (10²⁴) worlds in the universe.

Authors sometimes invent new worlds. They use these worlds as the settings for their stories. Some authors invent worlds that have magic.^[1]

World literature

World literature is literature that is read by many people all over our world. World literature is different from national literature.

I am more and more convinced that poetry is the universal possession of mankind, revealing itself everywhere and at all times in hundreds and hundreds of men. . . . I therefore like to look about me in foreign nations, and advise everyone to do the same. National literature is now a rather unmeaning term; the epoch of world literature is at hand. – Johann Wolfgang von Goethe, 1827

Worlds in literature

Creating a different world is a literary device used by authors to illustrate ideas. By placing the story in the setting of a different world, the author can change the way that things happen. For example, the author might imagine a world that has very little water or a world that has very little dry land. Deciding what a world looks like and how the world works is called world-building. Thinking about their world helps the author make good choices about what happens to the characters in the story. Some authors think about many details, such as what languages the characters speak and what the architecture is on the world.

Worlds in science fiction

Science fiction stories often use different worlds. Frank Herbert's famous Dune series focused on a world called Arrakis, which produced a very rare and very important spice.

Often a science-fiction story will involve multiple worlds. The Foundation series by Isaac Asimov was set in a galaxy with thousands of populated worlds. Asimov wrote the first books in the 1950s. In 1982, he published another book, called Foundation's Edge (ISBN 0385177259). The Star Wars movies had a several important worlds, and characters traveled between them. Some authors of science fiction worlds try to make them scrupulously obey the laws of physics.

Fantasy worlds

Fantasy worlds are fictional worlds that use magic. This magic may involve saying magic words, using magical objects, or performing magical rituals.

Examples of fantasy worlds
Author	World	Source	Description
J.R.R. Tolkien	Middle Earth	The Lord of the Rings trilogy	Middle-earth has some qualities similar to Mediæval Europe. The author added magical creatures like elves and wizards. At the end of the story, some magical creatures leave the world.
J.R.R. Tolkien	Arda	The Silmarillion	Arda is our world, but in a fictional time. Middle-earth is actually a continent of the world.
C. S. Lewis	Narnia	The Chronicles of Narnia series	The whole world is named after the principal country, Narnia. It features a powerful lion, an evil witch, giants, dragons, and some magical devices. This world is flat.
Piers Anthony	Xanth	The Magic of Xanth	This world has many magical things. It is connected to modern America. Each creature in Xanth has a unique magical talent. These talents are usually minor. Translating the book is difficult because of the many silly puns. These make sense in English but not necessarily in other languages.

Music

Music is made around the world.

The music may be a simple song for children, like this:

$<< \relative c'' { \key g \major \time 6/8 d4 b8 c4 a8 | d4 b8 g4 g8 | a4 b8 c[ b] a | d4 b8 g4. | } \addlyrics { Girls and boys come | out to play, The | moon doth shine _ as | bright as day; | } >>$

The music may be part of a complex symphony. This score shows part of a famous section of the Symphony No. 9 in D minor by Ludwig van Beethoven:

$<< \new StaffGroup << \new Staff { \set Staff.instrumentName = #"V1" \set Staff.midiInstrument = #"violin" \relative c'' { \time 4/4 \key d \major \clef treble fis2(_\markup { \dynamic p \italic dolce }^\markup { \italic arco } g4 a) | a4( g fis e) | d2( e4 fis) | fis4.( e8) e2 | } } \new Staff { \set Staff.instrumentName = #"V2" \set Staff.midiInstrument = #"violin" \relative c' { \time 4/4 \key d \major \clef treble fis4( d e fis) | d4.( e8 fis d b cis) | a4 a'2 a4( | a)( e cis8) e( fis g) | } } \new Staff { \set Staff.instrumentName = #"Va" \set Staff.midiInstrument = #"viola" \relative c'' { \time 4/4 \key d \major \clef alto a2( d,) | b4.( cis8 d4) g( | g)( fis e d)( | d)( cis b a) | } } \new Staff { \set Staff.instrumentName = #"Vc" \set Staff.midiInstrument = #"cello" \relative c'' { \time 4/4 \key d \major \clef bass a2( d,) | b4.( cis8 d4) g( | g)( fis e d)( | d)( cis b a) | } } \new Staff { \set Staff.instrumentName = #"Db" \set Staff.midiInstrument = #"contrabass" \relative c { \time 4/4 \key d \major \clef bass d1( | d)( | d4) d( cis b) | a2( a8) g'( fis e) | } } >> >>$

Languages in the world

The Egyptians used pictures to write their language. The pictures are called hieroglyphics. This is what they look like:

Once upon a time, Greek and Latin were spoken by most traders in the Western world. Before then, traders learned the languages of nearby cities. Ancient traders did not travel around the world.

Some languages are spoken in many parts of the world. These are called world languages. As of 2015, English is the most common world language. Previously, French was the most popular language in the West. Chinese was used by traders in all of East Asia for centuries. Arabic is common in the Middle East, Northern Africa, and other parts of the world.

World health

The World Health Organisation (French: Organisation mondiale de la santé) is an international organisation for public health.^[2] It is part of the United Nations. The World Health Organisation began in 1948.^[2] Its goal is for everyone in the world to be healthy and safe. It studies public health and tells governments and other organisations how to help people become healthy.

The organisation counts the number of people with health problems. These health problems include influenza, HIV infection, and depression. It also counts the number of people who have other problems, such as dirty water, hunger, and violence.

Mental health is also important.^[3] People with mental health problems such as depression often die ten years early.

The World Bank is also interested in health.^[4] Poor health affects the economy of a country.

Poetry

This poem by John Donne mentions the world:

Her death hath taught us dearly that thou art
Corrupt and mortal in thy purest part.
Let no man say, the world itself being dead,
'Tis labour lost to have discovered
The world's infirmities, since there is none
Alive to study this dissection;
For there's a kind of world remaining still,
Though she which did inanimate and fill
The world, be gone...

The entire poem can be read at Wikisource.

Shape of our world

Our world is not a perfect sphere. It is slightly flattened.

The mathematical formula for measuring the flatness of a sphere is

${\begin{aligned}f&={\frac {a-b}{a}}.\end{aligned}}$

For our world, ${\textstyle f\,\!}$ is approximately 0.3%. The Moon is rounder. For the Moon, ${\textstyle f\,\!}$ is approximately 0.1%. Jupiter is flatter. For Jupiter, ${\textstyle f\,\!}$ is approximately 6.5%.

Local planets

Our world is a planet. There are several types of planets in our solar system:

Terrestrial planets
Giant planets
- Gas giants
- Ice giants

These are the planets in our solar system:

Four terrestrial planets
1. Mercury
2. Venus
3. Earth
  - One satellite, called the Moon
4. Mars
Two gas giants
1. Jupiter
  - Four large satellites
  - 63 other satellites
2. Saturn
  - 62 satellites. Some are very small.
  - Seven are large. The largest, called Titan, is larger than the planet Mercury.
Two ice giants
1. Uranus
  - Five satellites
  - 22 other satellites
2. Neptune
  - One satellite, called Triton