Subcategories - Scientists
- 117,000-Year-Old Human Footprints Are Found Near South African Lagoon
- Abel Develops the First Artificial Kidney
- Abul Wefa
- Abuū Mūsā Jābir ibn Hayyān
- AIDS Scientists and Activists Meet in Amsterdam
- Al-Bīrūnī
- Albert A. Michelson
- Albert Calmette
- Alcmaeon
- Aleksandr Ivanovich Oparin
- Alessandro Volta
- Alexander Graham Bell
- Alexander Neckam
- Alexander von Humboldt
- Alfred Wegener
- Alhazen
- Amedeo Avogadro
- American Scientists Campaign Against Nuclear Testing
- Anaxagoras
- Anaximander
- Anaximenes of Miletus
- An Ancient Sanctuary Is Discovered in El Juyo Cave, Spain
- André-Louis Danjon
- Andrei Sakharov
- Andrews Discovers the First Fossilized Dinosaur Eggs
- Anschütz-Kaempfe Installs a Gyrocompass onto a German Battleship
- Anthropologists Claim That Ecuadorian Pottery Shows Transpacific Contact in 3000 b.c.e.
- Anthropologists Discover “Lucy,” an Early Hominid Skeleton
- Antoine-Laurent Lavoisier
- Antoni van Leeuwenhoek
- Apple II Becomes the First Successful Preassembled Personal Computer
- Archaeologists Unearth Ancient Scrolls
- Archimedes
- Ardrey’s The Territorial Imperative Argues That Humans Are Naturally Territorial
- Aretaeus of Cappadocia
- Aristotle Isolates Science as a Discipline
- Armstrong Perfects FM Radio
- Arnold of Villanova
- Arthur Holly Compton
- Artificial Fluoridation of Municipal Water Supplies to Prevent Dental Decay Is Introduced
- The Artificial Sweetener Cyclamate Is Introduced
- Asa Gray
- Asclepiades of Bithynia
- Aserinsky Discovers Rapid Eye Movement (REM) in Sleep and Dreams
- Aston Builds the First Mass Spectrograph and Discovers Isotopes
- Astronomers Discover an Unusual Ring System of Planet Neptune
- Astronomers Discover the Rings of the Planet Uranus
- August Krogh
- August Weismann
- Aulus Cornelius Celsus
