Wikipedia:List of articles all languages should have

Pencil and paper
Pencil and paper

There are hundreds of Wikipedias. Some of them are very big, and some are very small. They all need certain basic articles. They can even just be stubs.

This is a list of 1,000 basic articles every Wikipedia should contain. This page should include the same articles as meta:List of articles every Wikipedia should have/Version 1.4.

Some of the articles are in bold. That means that it is very important that they be written.

For a very long list of basic articles (10,000), see: Vital articles - expanded.

Section Number
Biography 204
Philosophy and psychology 18
World view and religion 25
Social sciences 70
Language and literature 47
Culture, arts and recreation 76
Science 299
* Astronomy 22
* Biology 120
** Health and medicine 37
* Chemistry 27
* Earth science 21
* Physics 39
* Measurement and units 6
* Timekeeping 6
* Foodstuffs 31
* Mathematics 25
Technology 70
History 45
Geography 146
Total 1000

Count checked: 16:16, 19 April 2010 (UTC)

Biography

Actors, dancers and models

  1. Sarah Bernhardt
  2. Charlie Chaplin
  3. Marlene Dietrich
  4. Marilyn Monroe

Artists and architects

  1. Le Corbusier
  2. Salvador Dalí
  3. Albrecht Dürer
  4. Vincent van Gogh
  5. Francisco de Goya
  6. Katsushika Hokusai
  7. Frida Kahlo
  8. Leonardo da Vinci
  9. Henri Matisse
  10. Michelangelo
  11. Pablo Picasso
  12. Raphael
  13. Rembrandt
  14. Peter Paul Rubens
  15. Mimar Sinan
  16. Diego Velázquez
  17. Andy Warhol
  18. Frank Lloyd Wright

Authors, playwrights and poets

  1. Abu Nuwas
  2. Hans Christian Andersen
  3. Bashō
  4. Jorge Luis Borges
  5. George Byron
  6. Miguel de Cervantes
  7. Geoffrey Chaucer
  8. Anton Chekhov
  9. Dante Alighieri
  10. Charles Dickens
  11. Fyodor Dostoyevsky
  12. Gabriel García Márquez
  13. Johann Wolfgang von Goethe
  14. Hafez
  15. Homer
  16. Victor Hugo
  17. James Joyce
  18. Franz Kafka
  19. Kālidāsa
  20. Li Bai
  21. Naguib Mahfouz
  22. Molière
  23. Ovid
  24. Marcel Proust
  25. Alexander Pushkin
  26. William Shakespeare
  27. Sophocles
  28. Rabindranath Tagore
  29. Leo Tolstoy
  30. Mark Twain
  31. Virgil

Composers and musicians

  1. Louis Armstrong
  2. Johann Sebastian Bach
  3. The Beatles
  4. Ludwig van Beethoven
  5. Johannes Brahms
  6. Frédéric Chopin
  7. Antonín Dvořák
  8. Georg Frideric Handel
  9. Joseph Haydn
  10. Gustav Mahler
  11. Wolfgang Amadeus Mozart
  12. Giovanni Pierluigi da Palestrina
  13. Édith Piaf
  14. Elvis Presley
  15. Giacomo Puccini
  16. Franz Schubert
  17. Igor Stravinsky
  18. Petr Tchaikovsky
  19. Giuseppe Verdi
  20. Antonio Vivaldi
  21. Richard Wagner

Explorers and travelers

  1. Roald Amundsen
  2. Neil Armstrong
  3. Jacques Cartier
  4. Christopher Columbus
  5. James Cook
  6. Hernán Cortés
  7. Yuri Gagarin
  8. Vasco da Gama
  9. Ibn Battuta
  10. Ferdinand Magellan
  11. Marco Polo
  12. Zheng He

Film directors and screenwriters

  1. Ingmar Bergman
  2. Walt Disney
  3. Sergei Eisenstein
  4. Federico Fellini
  5. Alfred Hitchcock
  6. Stanley Kubrick
  7. Akira Kurosawa
  8. Satyajit Ray
  9. Steven Spielberg

Inventors, scientists and mathematicians

  1. Archimedes
  2. Avicenna
  3. Tim Berners-Lee
  4. Brahmagupta
  5. Nicolaus Copernicus
  6. Marie Curie
  7. Charles Darwin
  8. Thomas Edison
  9. Albert Einstein
  10. Euclid
  11. Leonhard Euler
  12. Michael Faraday
  13. Enrico Fermi
  14. Henry Ford
  15. Galen
  16. Galileo Galilei
  17. Carl Friedrich Gauss
  18. Johannes Gutenberg
  19. David Hilbert
  20. James Prescott Joule
  21. Johannes Kepler
  22. Muhammad ibn Musa al-Khwarizmi
  23. Gottfried Wilhelm Leibniz
  24. Carl Linnaeus
  25. James Clerk Maxwell
  26. Dmitri Mendeleev
  27. Sir Isaac Newton
  28. Louis Pasteur
  29. Max Planck
  30. Ernest Rutherford
  31. Erwin Schrödinger
  32. Nikola Tesla
  33. Alan Turing
  34. James Watt

Philosophers and social scientists

  1. Aristotle
  2. Simone de Beauvoir
  3. Chanakya
  4. Noam Chomsky
  5. Confucius
  6. René Descartes
  7. Sigmund Freud
  8. Georg Wilhelm Friedrich Hegel
  9. Ibn Khaldun
  10. Immanuel Kant
  11. John Maynard Keynes
  12. Laozi
  13. John Locke
  14. Niccolò Machiavelli
  15. Karl Marx
  16. Friedrich Nietzsche
  17. Plato
  18. Jean-Jacques Rousseau
  19. Jean-Paul Sartre
  20. Sima Qian
  21. Adam Smith
  22. Socrates
  23. Voltaire
  24. Max Weber
  25. Ludwig Wittgenstein
  26. Zhu Xi

Political leaders

  1. Akbar
  2. Alexander the Great
  3. Ashoka
  4. Mustafa Kemal Atatürk
  5. Augustus
  6. Otto von Bismarck
  7. Simón Bolívar
  8. Napoleon Bonaparte
  9. Julius Caesar
  10. Charlemagne
  11. Winston Churchill
  12. Constantine the Great
  13. Cyrus the Great
  14. Charles de Gaulle
  15. Elizabeth I of England
  16. Mohandas Karamchand Gandhi
  17. Genghis Khan
  18. Che Guevara
  19. Adolf Hitler
  20. Joan of Arc
  21. Martin Luther King Jr.
  22. Vladimir Lenin
  23. Abraham Lincoln
  24. Louis XIV
  25. Rosa Luxemburg
  26. Nelson Mandela
  27. Mao Zedong
  28. Jawaharlal Nehru
  29. Kwame Nkrumah
  30. Peter the Great
  31. Qin Shi Huang
  32. Franklin D. Roosevelt
  33. Saladin
  34. Joseph Stalin
  35. Suleiman the Magnificent
  36. Sun Yat-sen
  37. Tamerlane
  38. Umar
  39. George Washington

Religious figures and theologians

  1. Abraham
  2. Thomas Aquinas
  3. Augustine of Hippo
  4. Buddha
  5. Al-Ghazali
  6. Jesus
  7. Martin Luther
  8. Moses
  9. Muhammad
  10. Paul the Apostle

Philosophy and psychology

Philosophy

  1. Beauty
  2. Dialectic
  3. Ethics
  4. Epistemology
  5. Feminism
  6. Free will
  7. Knowledge
  8. Logic
  9. Mind
  10. Philosophy
  11. Probability
  12. Reality
  13. Truth

Psychology

  1. Behavior
  2. Emotion
  3. Love
  4. Psychology
  5. Thought

Religion

World view and religion

  1. God
  2. Mythology
  3. Worldview philosophies
    1. Atheism
    2. Fundamentalism
    3. Materialism
    4. Monotheism
    5. Polytheism
  4. Soul
  5. Religion
  6. Specific religions
    1. Buddhism
    2. Christianity
      1. Catholic Church
    3. Confucianism
    4. Hinduism
      1. Trimurti
    5. Islam
      1. Shia Islam
    6. Jainism
    7. Judaism
    8. Sikhism
    9. Taoism
    10. Zoroastrianism
  7. Spiritual practices
    1. Sufism
    2. Yoga
    3. Zen

Social sciences

  1. Society
  2. Civilization
  3. Education

Family and relationships

  1. Family
  2. Child
  3. Man
  4. Marriage
  5. Woman

Politics

  1. Politics
  2. Anarchism
  3. Colonialism
  4. Communism
  5. Conservatism
  6. Democracy
  7. Dictatorship
  8. Diplomacy
  9. Fascism
  10. Globalization
  11. Government
  12. Ideology
  13. Imperialism
  14. Liberalism
  15. Marxism
  16. Monarchy
  17. Nationalism
  18. Republic
  19. Socialism
  20. State (polity)
  21. Political party
  22. Propaganda
  23. Terrorism

Business and economics

  1. Economics
  2. Capital
  3. Capitalism
  4. Currency
    1. Euro
    2. Japanese yen
    3. United States dollar
  5. Industry
  6. Money
  7. Tax

Law

  1. Law
  2. Constitution

International organizations

  1. African Union
  2. Arab League
  3. ASEAN
  4. Commonwealth of Independent States
  5. Commonwealth of Nations
  6. European Union
  7. International Red Cross and Red Crescent Movement
  8. NATO
  9. Nobel Prize
  10. OPEC
  11. United Nations
    1. International Court of Justice
    2. International Monetary Fund
    3. UNESCO
    4. Universal Declaration of Human Rights
    5. World Health Organization
  12. World Bank
  13. World Trade Organization

War and military

  1. Civil war
  2. Military
  3. Peace
  4. War

Social issues

  1. Abortion
  2. Capital punishment
  3. Human rights
  4. Racism
  5. Slavery

Language and literature

  1. Language
  2. Specific languages
    1. Arabic
    2. Bengali
    3. Chinese
    4. English
    5. Esperanto
    6. French
    7. German
    8. Greek
    9. Hebrew
    10. Hindi-Urdu
    11. Japanese
    12. Latin
    13. Persian
    14. Portuguese
    15. Russian
    16. Sanskrit
    17. Spanish
    18. Swahili
    19. Turkish
  3. Linguistics
  4. Grammar
  5. Word
    1. Phoneme
    2. Syllable
  6. Writing system
    1. Arabic alphabet
    2. Chinese characters
    3. Cyrillic script
    4. Greek alphabet
    5. Hangul
    6. Latin alphabet
  7. Literacy
  8. Translation
  9. Literature
    1. Prose
    2. The Art of War
    3. Fiction
      1. One Thousand and One Nights
    4. Novel
      1. Dream of the Red Chamber
      2. The Tale of Genji
    5. Poetry
      1. Epic of Gilgamesh
      2. Iliad
      3. Mahābhārata
      4. Shāhnāma

Science

  1. Science
  2. Nature

Astronomy

  1. Astronomy
  2. Asteroid
  3. Big Bang
  4. Black hole
  5. Comet
  6. Galaxy
    1. Milky Way
  7. Moon
  8. Planet
    1. Earth
    2. Jupiter
    3. Mars
    4. Mercury
    5. Neptune
    6. Saturn
    7. Uranus
    8. Venus
  9. Solar System
  10. Spaceflight
  11. Star
    1. Sun
  12. Universe

Biology

  1. Biology
  2. Biological materials
    1. DNA
    2. Enzyme
    3. Protein
  3. Botany
  4. Death
    1. Suicide
  5. Ecology
    1. Endangered species
  6. Domestication
  7. Life
  8. Biological classification
    1. Species

Biological processes

  1. Metabolism
    1. Digestion
    2. Photosynthesis
    3. Breathing
  2. Evolution
  3. Reproduction
    1. Pregnancy
    2. Sex

Anatomy

  1. Anatomy
  2. Breast
  3. Cell
  4. Circulatory system
    1. Blood
    2. Heart
  5. Endocrine system
  6. Human gastrointestinal tract
    1. Large intestine
    2. Small intestine
    3. Liver
  7. Muscle
  8. Nervous system
    1. Brain
    2. Sensory system
      1. Ear
      2. Nose
      3. Eye
  9. Reproductive system
  10. Respiratory system
    1. Lung
  11. Skeleton
  12. Skin

Health and medicine

  1. Medicine
  2. Addiction
  3. Alzheimer's disease
  4. Cancer
  5. Cholera
  6. Common cold
  7. Dentistry
  8. Disability
    1. Blindness
    2. Deafness
    3. Mental disorder
  9. Disease
  10. Pharmaceutical drug
  11. Ethanol
  12. Nicotine
    1. Tobacco
  13. Health
  14. Headache
  15. Immune system
  16. Heart attack
  17. Malaria
  18. Malnutrition
  19. Menstruation
  20. Obesity
  21. Pandemic
  22. Antibacterial
    1. Penicillin
  23. Pneumonia
  24. Poliomyelitis
  25. Sexually transmitted disease
    1. AIDS
  26. Stroke
  27. Tuberculosis
  28. Diabetes mellitus
  29. Virus
    1. Influenza
    2. Smallpox

Organisms

  1. Organism
  2. Animal
    1. Nematode
    2. Mollusc
    3. Arthropod
      1. Insect
        1. Ant
        2. Bee
        3. Mosquito
      2. Spider
    4. Chordate
      1. Amphibian
      2. Bird
        1. Chicken
        2. Pigeons and doves
      3. Fish
        1. Shark
      4. Mammal
        1. Camel
        2. Cat
        3. Cattle
        4. Dog
        5. Elephant
        6. Horse
        7. Sheep
        8. Rodent
        9. Domestic pig
        10. Primate
          1. Human
        11. Whales, dolphins and porpoises
      5. Reptile
        1. Dinosaur
        2. Snake
  3. Archaea
  4. Bacteria
  5. Fungus
  6. Plant
    1. Flower
    2. Tree
  7. Protist

Chemistry

  1. Chemistry
  2. Inorganic chemistry
  3. Biochemistry
  4. Chemical compound
    1. Acid
    2. Base (chemistry)
    3. Salt
  5. Chemical element
    1. Periodic table
    2. Aluminium
    3. Carbon
    4. Copper
    5. Gold
    6. Hydrogen
    7. Iron
    8. Nitrogen
    9. Oxygen
    10. Silver
    11. Tin
  6. Organic chemistry
    1. Alcohol
    2. Carbohydrate
    3. Hormone
    4. Lipid
  7. Molecule
  8. Analytical chemistry
  9. Physical chemistry

Earth science

  1. Avalanche
  2. Climate
    1. El Niño–Southern Oscillation
    2. Global warming
  3. Earthquake
  4. Geology
    1. Mineral
      1. Diamond
    2. Plate tectonics
    3. Rock
  5. Natural disaster
    1. Flood
    2. Tsunami
  6. Volcano
  7. Weather
    1. Cloud
    2. Rain
    3. Snow
    4. Tornado
    5. Tropical cyclone
    6. Wind

Physics

  1. Physics
  2. Acceleration
  3. Atom
  4. Energy
    1. Conservation of energy
  5. Electromagnetic radiation
    1. Infrared
    2. Ultraviolet
    3. Light
      1. Color
  6. Classical mechanics
  7. Force
    1. Electromagnetism
      1. Magnetic field
    2. Gravitation
    3. Strong interaction
    4. Weak interaction
  8. Magnet
  9. Mass
  10. Metal
    1. Steel
  11. Nuclear fission
  12. State of matter
    1. Gas
    2. Liquid
    3. Plasma
    4. Solid
  13. Quantum mechanics
  14. Radioactive decay
  15. General relativity
  16. Special relativity
  17. Semiconductor
  18. Sound
  19. Velocity
    1. Speed of light
  20. Temperature
  21. Time
  22. Thermodynamics
  23. Vacuum

Measurement and units

  1. Measurement
  2. Kilogram
  3. Litre
  4. Metre
  5. International System of Units
  6. Second

Timekeeping

  1. Calendar
    1. Gregorian calendar
  2. Clock
  3. Day
  4. Time zone
  5. Year

Foodstuffs

  1. Food
  2. Bread
  3. Cereal
    1. Barley
    2. Maize
    3. Oat
    4. Rice
    5. Rye
    6. Sorghum
    7. Wheat
  4. Cheese
  5. Chocolate
  6. Honey
  7. Fruit
    1. Apple
    2. Banana
    3. Grape
    4. Soybean
    5. Lemon
    6. Nut (fruit)
  8. Meat
  9. Sugar
  10. Vegetable
    1. Potato

Beverages

  1. Beer
  2. Coffee
  3. Juice
  4. Milk
  5. Tea
  6. Water
  7. Wine

Mathematics

  1. Mathematics
  2. Algebra
    1. Linear algebra
  3. Arithmetic
    1. Logarithm
  4. Coordinate system
  5. Mathematical analysis
    1. Differential equation
    2. Numerical analysis
  6. Equation
  7. Function (mathematics)
  8. Geometry
    1. Angle
    2. Area
    3. Pi
    4. Pythagorean theorem
    5. Symmetry
    6. Trigonometry
  9. Mathematical proof
  10. Number
    1. Complex number
    2. Number theory
  11. Infinity
  12. Set theory
  13. Statistics

Technology

  1. Technology
  2. Biotechnology
  3. Clothing
    1. Cotton
  4. Engineering
    1. Machine
    2. Robot
    3. Screw
    4. Wheel
  5. Agriculture
    1. Irrigation
    2. Plough
  6. Metallurgy
  7. Nanotechnology

Communication

  1. Communication
  2. Book
  3. Information
    1. Encyclopedia
  4. Journalism
    1. Newspaper
    2. Mass media
  5. Printing
  6. Telephone

Electronics

  1. Electronics
    1. Electric current
    2. Frequency
  2. Components
    1. Capacitor
    2. Inductor
    3. Transistor
    4. Diode
    5. Resistor
    6. Transformer

Computers and Internet

  1. Computer
    1. Hard disk drive
    2. Central processing unit
  2. Artificial intelligence
  3. Information technology
    1. Algorithm
  4. Internet
    1. Email
    2. World Wide Web
  5. Operating system
  6. Programming language
  7. Software

Energy and fuels

  1. Renewable energy
  2. Electricity
    1. Nuclear power
  3. Fossil fuel
  4. Internal combustion engine
  5. Steam engine
  6. Fire

Materials

  1. Glass
  2. Paper
  3. Plastic
  4. Wood

Transportation

  1. Transport
  2. Aircraft
  3. Automobile
  4. Bicycle
  5. Submarine
  6. Ship
  7. Train

Weapons

  1. Weapon
    1. Sword
    2. Firearm
      1. Machine gun
    3. Nuclear weapon
  2. Tank
  3. Explosive material
    1. Gunpowder

Arts and recreation

  1. Culture
  2. Art
    1. Comics
    2. Painting
    3. Photography
    4. Sculpture
    5. Pottery
  3. Dance
  4. Fashion
  5. Theatre
  6. Calligraphy

Architecture and civil engineering

  1. Architecture
  2. Arch
  3. Bridge
  4. Canal
  5. Dam
  6. Dome
  7. House
  8. Specific structures
    1. Angkor Wat
    2. Colosseum
    3. Great Wall of China
    4. Eiffel Tower
    5. Empire State Building
    6. Hagia Sophia
    7. Parthenon
    8. Giza Necropolis
    9. St. Peter's Basilica
    10. Statue of Liberty
    11. Taj Mahal
    12. Three Gorges Dam
  9. Pyramid
  10. Tower

Film, radio and television

  1. Film
    1. Animation
      1. Anime
  2. Radio
  3. Television

Music

  1. Music
  2. Song
  3. Specific music genres
    1. Blues
    2. Classical music
      1. Opera
      2. Symphony
    3. Electronic music
    4. Flamenco
    5. Hip hop
    6. Jazz
    7. Reggae
    8. Rock music
    9. Samba
  4. Specific musical instruments
    1. Drum
    2. Flute
    3. Guitar
    4. Piano
    5. Trumpet
    6. Violin

Recreation

  1. Game
    1. Backgammon
    2. Chess
    3. Go (game)
  2. Gambling
  3. Martial arts
    1. Karate
    2. Judo
  4. Olympic Games
  5. Sport
    1. Athletics
    2. Auto racing
    3. Baseball
    4. Basketball
    5. Cricket
    6. Association football
    7. Golf
    8. Rugby
    9. Tennis
  6. Toy

History and geography

History

This section is for events and periods in human history and prehistory. At least five sentences on:

  1. History

Prehistory and ancient world

  1. Prehistory
  2. Stone Age
  3. Bronze Age
  4. Iron Age
  5. Mesopotamia
  6. Ancient Egypt
  7. Ancient Greece
  8. Roman Empire
  9. Han Dynasty
  10. Gupta Empire

Middle Ages and Early Modern

  1. Abbasid Caliphate
  2. Age of Enlightenment
  3. Aztec
  4. Byzantine Empire
  5. Crusades
  6. Holy Roman Empire
  7. Hundred Years' War
  8. Middle Ages
  9. Mongol Empire
  10. Ming Dynasty
  11. Ottoman Empire
  12. Protestant Reformation
  13. Thirty Years' War
  14. Renaissance
  15. Tang Dynasty
  16. Vikings

Modern

  1. Arab-Israeli conflict
  2. American Civil War
  3. Apartheid
  4. British Empire
  5. Cold War
  6. Cultural Revolution
  7. French Revolution
  8. Great Depression
  9. The Holocaust
  10. Industrial Revolution
  11. Nazi Germany
  12. Meiji Restoration
  13. Russian Revolution
  14. Qing Dynasty
  15. Treaty of Versailles
  16. Vietnam War
  17. World War I
  18. World War II

Geography

This section is for geographical concepts and for specific places.

  1. Geography
  2. City
  3. Continent
  4. Forest
  5. Mountain
  6. Desert
  7. North Pole
  8. Ocean
  9. River
  10. Sea
  11. South Pole

Continents and major regions

  1. Africa
  2. Antarctica
  3. Asia
  4. Europe
  5. Middle East
  6. North America
  7. Oceania
  8. South America

Countries

Eventually, there should be articles on most or all of the countries listed at List of countries. However, for the smaller Wikipedias, some of the more high-priority countries to have articles on are:

  1. Afghanistan
  2. Algeria
  3. Argentina
  4. Australia
  5. Austria
  6. Bangladesh
  7. Brazil
  8. Canada
  9. China
  10. Democratic Republic of the Congo
  11. Cuba
  12. Egypt
  13. Ethiopia
  14. France
  15. Germany
  16. India
  17. Indonesia
  18. Iran
  19. Iraq
  20. Israel
  21. Italy
  22. Japan
  23. Mexico
  24. Netherlands
  25. New Zealand
  26. Nigeria
  27. Pakistan
  28. Poland
  29. Portugal
  30. Russia
  31. Saudi Arabia
  32. Singapore
  33. South Africa
  34. South Korea
  35. Spain
  36. Sudan
  37. Switzerland
  38. Tanzania
  39. Thailand
  40. Turkey
  41. Ukraine
  42. United Kingdom
  43. United States
  44. Vatican City
  45. Venezuela
  46. Vietnam

Cities

  1. Amsterdam
  2. Athens
  3. Baghdad
  4. Bangkok
  5. Beijing
  6. Berlin
  7. Bogotá
  8. Brussels
  9. Buenos Aires
  10. Cairo
  11. Cape Town
  12. Damascus
  13. Delhi
  14. Dhaka
  15. Dubai
  16. Hong Kong
  17. Istanbul
  18. Jakarta
  19. Jerusalem
  20. Karachi
  21. Kinshasa
  22. Kolkata
  23. Lagos
  24. London
  25. Los Angeles
  26. Madrid
  27. Mecca
  28. Mexico City
  29. Moscow
  30. Mumbai
  31. Nairobi
  32. New York City
  33. Paris
  34. Rio de Janeiro
  35. Rome
  36. Saint Petersburg
  37. São Paulo
  38. Seoul
  39. Shanghai
  40. Sydney
  41. Tehran
  42. Tokyo
  43. Vienna
  44. Washington, D.C.

Bodies of water

  1. Amazon River
  2. Arctic Ocean
  3. Atlantic Ocean
  4. Baltic Sea
  5. Black Sea
  6. Caribbean Sea
  7. Caspian Sea
  8. Congo River
  9. Danube
  10. Ganges
  11. Great Barrier Reef
  12. Great Lakes
  13. Indian Ocean
  14. Indus River
  15. Lake Baikal
  16. Lake Tanganyika
  17. Lake Victoria
  18. Mediterranean Sea
  19. Mississippi River
  20. Niger River
  21. Nile
  22. North Sea
  23. Pacific Ocean
  24. Panama Canal
  25. Rhine
  26. Suez Canal
  27. Southern Ocean
  28. Volga River
  29. Yangtze River
  30. Yellow River

Mountains and deserts

  1. Alps
  2. Andes
  3. Himalayas
    1. Mount Everest
  4. Mount Kilimanjaro
  5. Rocky Mountains
  6. Sahara