A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A For Andromeda
"A" series of German rockets
A star
a'a
abacus
abalone
Abbott, Edwin Abbott (1838–1926)
Abbott, Ira H. (1906–1988)
abc conjecture
abdomen
abducens nerve
abduction and adduction
Abel, John Jacob (1857–1938)
Abel, Niels Henrik (1802–1829)
Abell cluster
Aberdeen Proving Ground
aberration, optical
aberration of starlight
abiogenesis
ablation
Able
abracadabra
abrasive
abscess
abscission
absolute
absolute magnitude
absolute value
absolute zero
absorbed dose
absorptance
absorption
absorption spectrum
abstract algebra
Abu'l Wafa (AD 940–998)
abundant number
Abyss, The
abyssal zone
AC circuit
acanthion
Acathocephala (spiny-headed worms)
acapulcoite
Acarina
acceleration
acceleration due to gravity (g)
accelerator
accessory nerve
acclimatization
accommodation
accretion
accretion disk
accretionary lapilli
accuracy
ACE (Advanced Composition Explorer)
ACE inhibitor
acetabulum
acetaldehyde
acetic acid
acetyl coenzyme A
acetylcholine
acetylene
achene
Achernar (Alpha Eridani)
Acheson, Edward Goodrich (1856–1931)
Achilles (minor planet 588)
Achilles tendon
achondrite
achondroplasia
acid
acid anhydride
acid chloride
acid rain
acid salt
acidophiles
acidosis
Ackermann function
acne
acoustic shielding
acoustics
ACOUSTICS AND MUSIC
acquired immune deficiency syndrome (AIDS)
acquisition
acridine
ACRIMSAT (Active Cavity Radiometer Irradiance Monitor Satellite)
acromegaly
acromion
Acrux (Alpha Crucis)
actin
actinide
actinium
Actinopterygii (ray-finned fish)
action
action at a distance
activation cross section
activation energy
active beam
active fault
active galactic nucleus
active site
active transport
activity
ACTS (Advanced Communications Technology Satellite)
acupuncture
acute
acute respiratory distress syndrome
acyl group
Adams, John (1735–1826)
Adams, John Couch (1819–1892)
Adams, Walter Sidney (1876–1956)
Adam's apple
adaptation
adaptive optics
addiction
Addison, Joseph (1672–1719)
Addison's disease
addition
addition reaction
adductor magnus
ADE (Air Density Explorer)
adenine
adenoids
adenosine triphosphate (ATP)
adenovirus
adenovirus infection
ADEOS (Advanced Earth Observing Satellite)
Adhara (Epsilon Canis Majoris)
ADHD (Attention Deficit–Hyperactive Disorder)
adhesion
adiabatic process
adipose tissue
admittance
Adrastea
adrenal gland
adrenaline
adrenocorticotropic hormone (ACTH)
adsorption
advance of perihelion
Advanced Composition Explorer (ACE)
ADVANCED PROPULSION CONCEPTS
adventitious
AE Aurigae
AEM (Applications Explorer Mission)
aeolipile
aerial
Aerial Target (AT)
Aerobee
aerobraking and aerocapture
aerodynamics
AERODYNAMICS AND AERONAUTICS
aeroembolism
aerogel
aeronautics
aeronomy
Aeros
aerosol
aerospace
AEROSPACE ADMINISTRATORS
aerospace and related companies
aerospace medicine
aerospike engine
affine geometry
African rainforest
afterburner
afterglow
agar
Agassiz, Alexander (1835–1910)
agate
agave
Agena
agglomerate
agglutinates
agglutinin
aging
Agnatha (jawless fish)
Agnesi, Maria Gaetana (1718–1799)
Ahrens, Wilhelm Ernst Martin Georg (1872–1927)
AI Velorum star
AIDS
Aiken, Howard (1900–1973)
aileron
AIM (Aeronomy of Ice in the Mesosphere)
air
air brake
air sac
air speed indicator
air-breathing engine
airfoil
airglow
airlock
airmass
airplane
airship
airspace
airways
Airy, George Biddell (1801–1892)
Airy disk
Aitken, Robert Grant (1864–1951)
Akebono
Akiyama, Tokohiro (1944–)
Al Niyat (Sigma and Tau Scorpii)
Alais meteorite
alanine
Albategnius (al-Battani, Muhammad ibn Jabir) (c. 850–929)
albedo
Albertus Magnus (1193–1280)
albino
Albireo (Beta Cygni)
albumin
Alcantara Launch Center
alchemy
alcohol
Alcubierre warp drive
Alcuin (735–804)
Alcyone (Eta Tauri)
Aldebaran (Alpha Tauri)
aldehyde
Alder, Kurt (1902–1958)
Alderamin (Alpha Cephei)
aldosterone
Aldrin, Edwin Eugene ("Buzz"), Jr. (1930–)
Alembert, Jean le Rond d' (1717–1783)
alembic
aleph
Alexander's Horned Sphere
Alexandra family (of asteroids)
ALEXIS (Array of Low Energy X-ray Imaging Sensors)
Alfirk (Beta Cephei)
Alfvén, Hannes Olof Gösta (1908–1995)
algae
ALGEBRA
algebra
algebraic function
algebraic geometry
algebraic number
algebraic topology
Algieba (Gamma Leonis)
Algol (Beta Persei)
Algonquin Radio Observatory
algorithm
algorithmic complexity
ALH 84001
Alhambra
Alhazen (Abu Ali al Hassan ibn al Haitham) (c. 965–c. 1040)
Alhena (Gamma Geminorum)
alicyclic compound
alien
Alien
alien life, a gallery of possibilities
alimentary canal
Alinda group (of asteroids)
Alioth (Epsilon Ursae Majoris)
aliphatic compound
aliquot part
alizarin
Alkaid (Eta Ursae Majoris)
alkali
alkali metal
alkaline battery
alkaline earth metal
alkaliphile
alkaloid
alkalosis
alkanes
alkenes
Al-Khowarizmi (c. 780–850)
alkynes
Allais paradox
Allan Hills
allantois
Allegheny Observatory
allele
Allen, Irwin (1916–1991)
Allen Telescope Array (ATA)
Allende meteorite
allergy
allogenic
allopatric speciation
allotropy
alloy
all-sky camera
all-sky survey
alluvial fan
alluvium
ALMA
Almaak (Gamma Andromedae)
Almagest
almanac
Almaz
almond tree
almost perfect number
Alnair (Alpha Gruis)
Alnath (Beta Tauri)
Alnilam (Epsilon Orionis)
Alnitak (Zeta Orionis)
alopecia
ALOS (Advanced Land Observing Satellite)
Alouette
Alpha Centauri
alpha particle
alpha-1 antitrypsin deficiency
Alpha² Canum Venaticorum star
alphametic
Alphard (Alpha Hydrae)
Alphekka (Alpha Coronae Borealis)
Alpher, Ralph Asher (1921–2007)
Alpheratz (Alpha Andromedae)
Alphonsine Tables
Alphonsus
Al-Sufi, Abd al-Rahman (AD 903–986)
Altair (Alpha Aquilae)
altazimuth mounting
Altekruse puzzle
alternation of generations
alternate
alternating current
ALTERNATIVE FORMS OF LIFE
altimeter
altitude
altitude sickness
Aludra (Eta Canis Majoris)
aluminum
Alvarez, Luis Walter (1911–1988)
alveolus
AM Canum Venaticorum star
AM Herculis star
Am star
Amalthea
Ambartsumian, Viktor Amazaspovich (1908–1996)
Ambartsumian's Knot
amber
ambiguous figure
ambipolar diffusion
American Astronautical Society
American Institute of Aeronautics and Astronautics
American Rocket Society
americium
Ames, Milton B. (1913–1992)
Ames Research Center
Ames room
amethyst
amicable numbers
amide
amine
amino acids
amino acids, in space
amino group
ammeter
ammonia
ammonia-based life
ammonite
amnesia
amniocentesis
amniotic sac
amoeba
Amor group
amorphous
amorphous semiconductor
amount of substance
Ampère, André Marie (1775–1836)
ampere
amphibian
amphibians and reptiles, unusual
amphibole
amphipod
amphoteric
amplifier
amplitude
amplitude modulation
AMPTE (Active Magnetosphere Particle Tracer Explorer)
AMS (Alpha Magnetic Spectrometer)
amygdala
amyl compound
amylase
amyloid
amyloidosis
amyotrophic lateral sclerosis
anabolism
anacoustic zone
anaerobe
anagram
analemma
analgesic
anallagmatic curve
analogous
analysis
ANALYTICAL CHEMISTRY
analytical geometry
ANALYTICAL GEOMETRY
anamorphosis
Ananke
anaphase
anaphylaxis
anaplasmosis
anastigmat(ic)
anastomosis
"anatomical snuffbox"
anatomy
ANATOMY AND PHYSIOLOGY
Anaxagoras of Clazomenae (c. 500–c. 428 BC)
Anaximander of Miletus (c. 610–c. 540 BC)
Anaximenes of Miletus (c. 585–525 BC)
ancient philosophy, related to the possibility of extraterrestrial life
ancient science
andalusite
Anders, William Alison (1933–)
Anderson, Carl David (1905–1991)
andesite
Andøya Rocket Range
Andrews Air Force Base
androecium
androgen
android
Andromeda (constellation)
Andromeda Galaxy (M31, NGC 224)
andromonoecious
anechoic chamber
anemia
anemometer
anemophily
anencephaly
anesthesia
aneurysm
Angara
Angelina (minor planet 64)
angina
angiography
angioplasty
angiosperm
angiotensin
angle
angle of attack
angle of incidence
angle of refraction
anglesite
Anglo-Australian Observatory
angrite
angstrom (Å)
Ångström, Anders Jonas (1814–1874)
angular diameter
angular momentum
anhydrite
anhydrobiosis
Anik
aniline
animal
animal behavior
animal cell
animals in space
animals' mathematical ability
ankle
Annelida (true worms)
annihilation
annual (plant)
annual ring
annual variation
annulus
anode
anodizing
anomaly
anorthosite
ANS (Astronomische Nederlandse Satelliet)
ansa
Ansari X-prize
ant
Ant Nebula (Menzel 3)
antagonist
Antarctic Dry Valleys
Antarctic Search for Meteorites (ANSMET)
Antares (Alpha Scorpii)
antenna (physics)
antenna (zoology)
Antennae (NGC 4038 and NGC 4039)
anterior
anterior facial vein
anther
antheridium
anthocyanin
Anthony, Piers (1934–)
anthracene
anthracite
anthrax
anthropic principle
anthropology
anthropomorphism
antibiotic
antibody
anticline
anticoagulant
anticyclone
antidiuretic hormone (ADH)
anti-g suit
antigen
antigravity
antigravity houses and hills
antihistamine
Antikythera mechanism
antimatter
antimatter propulsion
antimony
Antiope (minor planet 90)
antioxidant
antiparticles
antiphospholipid antibody syndrome
antiprism
antisense
antiseptic
antitail
antitoxin
antlerite
Antlia (constellation)
Antlia Dwarf Galaxy
Antoniadi, Eugene Michael (1870–1944)
Anura
anus
AO Cassiopeiae
aorta
aortic valve
Apache Point Observatory
apatite
ape
apergy
aperiodic tiling
aperture
aperture synthesis
Apéry's constant
apex (astronomy)
apex (mathematics)
aphasia
aphelion
aphid
apical meristem
aplastic anemia
apoapsis
apocrine gland
Apoda
apogee
apohele
Apollo 7
Apollo 8
Apollo 9
Apollo 10
Apollo 11
Apollo 12
Apollo 13
Apollo 14
Apollo 15
Apollo 16
Apollo 17
Apollo group
Apollo Project
Apollonius of Perga (c. 262–c. 190 BC)
Apollo-Soyuz Test Project
Apophis (minor planet 99942)
apoptosis
apothecaries' weights
apothem
apparent horizon
apparent magnitude
apparition
appendicitis
appendix
Appleton, Edward Victor (1892–1965)
approximation
APPROXIMATIONS AND AVERAGES
apsis
Apus (constellation)
Aqua
aqua regia
aqualung
Aquarids
Aquarius (constellation)
Aquarius (spacecraft)
aqueous humor
Aquila (constellation)
aquifer
Aquinas, Thomas (1225–1274)
Ara (constellation)
Arabian astronomy
Arabic numerals
arachnid
arachnoid membrane
Arago, Dominique Francois Jean (1786–1853)
Arago point
aragonite
arbelos
arc
arc lamp
Arcetri Astrophysical Observatory
arch
archaea
Archaeopteryx
archegonium
archenteron
archeoastronomy
Arches Cluster
Archimedean screw
Archimedean solid
Archimedean spiral
Archimedean tessellation
Archimedes (c. 287–212 BC)
Archimedes and the burning mirrors
Archimedes' cattle problem
Archimedes' principle
archipelago
Archytas (c. 428–c. 350 BC)
arcjet
arcsecond and arcminute
Arcturus (Alpha Bootis)
area
area rule
Arecibo message
Arecibo Observatory
Arecibo radio telescope
Arend-Roland, Comet (C/1956 R1)
areolar tissue
Ares (launch vehicles)
Ares Vallis
arète
Argand burner
Argand diagram
Argelander, Friedrich Wilhelm August (1799–1875)
arginine
Argo Navis
argon
ARGOS (Advanced Research and Global Observation Satellite)
argument
argument of perihelion
Argus, Project
Ariane
Ariel (moon of Saturn)
Ariel (UK satellites)
Aries (constellation)
Aries sounding rocket
Ariosto, Ludovico (1474–1533)
Aristarchus (crater)
Aristarchus of Samos (c. 320–c. 250 BC)
Aristotle of Stagira (384–322 BC)
Aristotle's wheel
arithmetic
ARITHMETIC
arithmetic mean
arithmetic sequence
arkose
Arkwright, Richard (1732–1792)
arm
armature
armillary sphere
Armstrong, Neil Alden (1930–2012)
Arnold, Henry H. (Hap) (1886–1950)
aromatic compound
aromatic herbs
Arouet, Francois-Marie (1694–1778)
Around the Moon
Arp, Halton Christian (1927–2013)
array
Arrest, Heinrich Ludwig d' (1822–1875)
Arrhenius, Svante August (1859–1927)
arrhythmias
arrow of time
Arrow paradox
arsenic
arsenic-based life
arsenopyrite
ARTEMIS (Advanced Relay Technology Mission)
arterial blood gas analysis
arteriography
arteriole
arteriosclerosis
artery
arthritis
arthropod
arthroscope
articular capsule
artifacts, alien
artificial gravity
artificial insemination
artificial intelligence
artificial life
artificial selection
Artiodactyla
ARTV (Advanced Reentry Test Vehicle)
Aryabhata (AD 476–550)
aryl group
arytenoid cartilages
Arzachel (Al-Zarqali, Abu Ishaq Ibrahim ibn Yahya) (1028–1087)
asbestos
Asperger syndrome
Asbolus (minor planet 8405)
ASCA
ascariasis
ascending node
ascending pharyngeal artery
Asclepius (minor planet 4581)
Ascomycetes
asexual reproduction
ash
Asiago Astrophysical Observatory
Asian and medieval science
Asimov, Isaac (1920–1992)
ASLV (Advanced Satellite Launch Vehicle)
asparagine
aspartame
aspect
aspect ratio
asphalt
asphyxia
aspirin
assay
assaying
ASSET (Aerothermodynamic Elastic Structural Systems Environmental Tests)
associationism
associations, stellar
associative
astatine
asterism
Asterix
asteroid
asteroid belt
asteroid mining
asteroid spectral types
ASTEROIDS, CENTAURS, AND KUIPER BELT OBJECTS: INDIVIDUAL
ASTEROIDS AND OTHER MINOR PLANETS: TYPES AND GROUPS
asthenosphere
asthma
astigmatism
Aston, Francis William (1877–1945)
Astraglossa
astringent
Astro (shuttle science payload)
Astro- (Japanese satellites)
Astro-E
Astro-F
ASTROBIOLOGY
astrobiology
Astrobiology Institute
astrobleme
astrochemistry
astrocyte
astroengineering
Astrographic Catalogue
astroid
astrolabe
astrometry
Astron
ASTRONAUTS AND COSMONAUTS
Astronomer Royal
ASTRONOMERS AND ASTROPHYSICISTS
Astronomical Almanac
ASTRONOMICAL CATALOGUES
ASTRONOMICAL QUANTITIES
astronomical unit
Astronomische Gesellschaft Katalog
astronomy
astrophotography
ASTROPHYSICAL PHENOMENA
astrophysics
astroseismology
astrosociology
Asuka
asymmetric drift
asymptote
asymptotic giant branch
Atacama Large Millimeter Array
atavism
ataxia
ataxite
Atchley, Jr., Dana W.
Aten group
Athena (launch vehicle)
atherosclerosis
athlete's foot
Atiyah, Michael Francis (1929–2019)
Atlantic Missile Range
Atlantis (Shuttle orbiter)
Atlantis, legend of
Atlas (launch vehicle)
Atlas (moon)
ATLAS particle detector
atmosphere
atmosphere of Earth
atmosphere (unit)
atmospheric braking
atmospheric circulation
atmospheric extinction
atmospheric halo
ATMOSPHERIC PHENOMENA AND STRUCTURES
atmospheric pressure
atmospheric refraction
atmospheric window
atoll
atom
ATOMIC AND NUCLEAR PHYSICS
atomic bomb
atomic clock
atomic force microscope
atomic mass
atomic number
atomic orbital
atomic structure and periodic table
atomic theory of matter
atomism
Atoms For Peace Galaxy (NGC 7252)
Atomium, The
atopic dermatitis
ATP
Atria (Alpha Trianguli Australis)
atrial natriuretic peptide (ANP)
atrial fibrillation
atrial septal defect (hole-in-the-heart)
atrium
atropine
ATS (Applications Technology Satellite)
attitude
attractor
A-type asteroid
Aubel's theorem
aubrite
auditory canal
auditory nerve
auditory ossicles
Auger, Pierre Victor (1899–1993)
Auger effect
augite
Augustine, Norman R. (1935–)
Aura
auricle
Auriga (constellation)
aurora
Australia Telescope National Facility (ATNF)
Australian desert grasslands
Australian Space Research Institute
australopithecine
autism
autoclave
autogyro
autoimmune disease
autoimmune lymphoproliferative syndrome (ALPS)
automated external defibrillator
Automated Transfer Vehicle
automobile
automorphic number
automorphism
autonomic nervous system
autopilot
autopoeisis
autosomal dominant
autosomal recessive
autosome
autotrophs
auxin
avalanche
Averroës (1126–1198)
Avdeyev, Sergei (1956–)
average
averted vision
AVIATION PIONEERS
avionics
Avior (Epsilon Carinae)
Avogadro, Amedeo (1776–1856)
Avogadro constant
avoirdupois
Avrocar
Axelrod, Julius (1912–2004)
axil
axilla
axillary artery
axillary vein
axiom of choice
axion
axis
axis of symmetry
axolotl
axon
azathioprine
azeotropic mixture
azimuth
azimuthal quantum number
azo compound
Azur
azurite