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A For Andromeda
a priori
"A" series of German rockets
A star
a'a
AAA
AAO
Aaronson, Marc (1950–1987)
AAT
abacus
abalone
Abbott, Edwin Abbott (1838–1926)
Abbott, Ira H. (1906–1988)
ABC conjecture
abdomen
abducens nerve
abduction
Abel, John Jacob (1857–1938)
Abel, Niels Henrik (1802–1829)
Abelian group
Abell 39
Abell cluster
Aberdeen Proving Ground
aberration, optical
aberration of starlight
abiogenesis
abiotic
ablation
Able
ABMA (Army Ballistic Missile Agency)
abort
abracadabra
abrasion
abrasive
abscess
abscisic acid
abscissa
abscission
absolute
Absolute Astronomical Accelerometry
absolute humidity
absolute magnitude
absolute space and time
absolute value
absolute zero
absorbed dose
absorber
absorptance
absorption
absorption band
absorption line
absorption nebula
absorption spectrum
absorptive feeder
abstract algebra
Abu'l Wafa (AD 940–998)
abundance, of elements
abundant number
Abyss, The
abyssal zone
acanthion
Acathocephala (spiny-headed worms)
acapulcoite
Acarina
Acasta Formation
acceleration
acceleration due to gravity (g)
acceleration stress
acceleration tolerance
accelerator
accelerometer
ACCESS (Advanced Cosmic-ray Composition Experiment on the Space Station)
access time
accessory nerve
accessory organ
accessory pigment
acclimatization
accommodation
accretion
accretion disk
accretionary lapilli
accretionary wedge
accuracy
ACE (Advanced Composition Explorer)
ACE inhibitor
acebutolol
acellular
acephalous
acetabulum
acetaldehyde
acetate
acetic acid
acetogens
acetone
acetyl coenzyme A
acetylcholine
acetylcysteine
acetylene (C2H2)
achene
Achernar (Alpha Eridani)
Acheson, Edward Goodrich (1856–1931)
Achilles (minor planet 588)
Achilles tendon
achlamydeous
achondrite
achondroplasia
achromatic
acid
acid anhydride
acid chloride
acid number
acid rain
acid rock
acid salt
acidic
acidophiles
acidosis
Ackermann function
A-class asteroid
acne
acosmism
acoustic sheilding
acoustics
ACOUSTICS AND MUSIC
acquired immune deficiency syndrome (AIDS)
acquisition
acridine
ACRIMSAT (Active Cavity Radiometer Irradiance Monitor Satellite)
acre
acromegaly
acromion
Acrux (Alpha Crucis)
ACRV (Assured Crew Return Vehicle)
acrylic
ACT Catalog
actin
actinide
actinium
actinomycetes
Actinopterygii (ray-finned fish)
action
action at a distance
action potential
activation cross section
activation energy
active beam
active fault
active galactic nucleus
active galaxy
active optics
active region
active satellite
active site
active sun
active transport
activity
actomyosin
ACTS (Advanced Communications Technology Satellite)
actuator
acupuncture
acute
acute respiratory distress syndrome
acyl group
Ad Astra Rocket Company
Adams, John (1735–1826)
Adams, John Couch (1819–1892)
Adams, Walter Sidney (1876–1956)
Adam's apple
Adamski, George (1891–1965)
adaptation
adapter skirt
adaptive optics
adaptive radiation
addend
addiction
Addison, Joseph (1672–1719)
Addison's disease
addition
addition reaction
additive
address
adduction
adductor magnus
ADE (Air Density Explorer)
adenine
adenoids
adenosine diphosphate (ADP)
adenosine monophosphate (AMP)
adenosine triphosphate (ATP)
adenovirus
adenovirus infection
ADEOS (Advanced Earth Observing Satellite)
Adhara (Epsilon Canis Majoris)
ADHD (Attention Deficit–Hyperactive Disorder)
adhesion
adhesive
adiabatic process
adipose tissue
adjacent
Adler, Clément (1841–1926)
admittance
Adonis (minor planet 2101)
Adrastea
adrenal gland
adrenaline
adrenocorticotropic hormone (ACTH)
adsorption
advance of perihelion
Advanced Composition Explorer (ACE)
Advanced Fiber-Optic Echelle spectrometer (AFOE)
ADVANCED PROPULSION CONCEPTS
Advanced Quantum/Relativity Theory Propulsion Workshop (1994)
advanced wave
adventitious
AE Aurigae
Ae star
AEM (Applications Explorer Mission)
aeolian structure
aeolipile
aeration
aerenchyma
aerial
Aerial Phenomena Research Organization (APRO)
Aerial Target (A.T.)
aeroballistics
aerobe
Aerobee
aerobic
aerobraking
aerocapture
aerodynamics
AERODYNAMICS AND AERONAUTICS
aeroembolism
aerogel
Aerojet Corporation
aerolite
aeronautics
aeronomy
aeropause
Aeros
aerosol
aerospace
AEROSPACE ADMINISTRATORS
AEROSPACE AND RELATED COMPANIES
aerospace medicine
aerothermodynamic border
aestivation
affine geometry
AFOE
AFSATCOM (Air Force Satellite Communications System)
afterbirth
afterburner
afterburning
afterglow
after-image
aftershock
aft-firing thrusters
agar
Agassiz, Alexander (1835–1910)
agate
Agena
agglomerate
agglutinates
agglutination
agglutinin
aging
AGN
Agnatha (jawless fish)
Agnesi, Maria Gaetana (1718–1799)
agranulocytosis
agravic
Agrest, Matest M. (1915–2005)
Agrest, Mikhail
Ahnighito meteorite
Ahrens, Wilhelm Ernst Martin Georg (1872–1927)
AI Velorum star
AIDS
Aiken, Howard (1900–1973)
aileron
AIM (Aeronomy of Ice in the Mesophere)
air
air brake
air breakup
air conditioner
Air Force Flight Test Center
Air Force Space Command
Air Materiel Command (AMC)
air sac
air speed indicator
air start
Air Technical Intelligence Center (ATIC)
air-breathing engine
airfoil
airframe
airglow
airlock
airmass
airplane
airship
airspace
airways
Airy, George Biddell (1801–1892)
Airy disk
Aitken, Robert Grant (1864–1951)
Aitken Double Star Catalogue (ADS)
Akebono
Akiyama, Tokohiro (1944–)
Al Niyat (Sigma and Tau Scorpii)
alabaster
Alais meteorite
alanine
Albategnius (al-Battani, Muhammad ibn Jabir) (c.850–929)
albedo
albedo feature
Albertus Magnus (1193–1280)
albino
Albireo (Beta Cygni)
albite
albumin
Alcantara Launch Center
alchemy
alcohols
Alcubierre, Miguel (1964–)
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
Alencon Spaceman
aleph
Alexander's Horned Sphere
Alexandra family (of asteroids)
Alexandrian school
ALEXIS (Array of Low Energy X-ray Imaging Sensors)
Alfirk (Beta Cephei)
Alfvén, Hannes Olof Gösta (1908–1995)
algae
ALGEBRA
algebra
algebraic curve
algebraic function
algebraic geometry
algebraic number
algebraic number theory
algebraic operation
algebraic topology
Algieba (Gamma Leonis)
algin
Algol (Beta Persei)
Algol star
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 abduction
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 flats
alkali metal
alkaline
alkaline battery
alkaline earth metal
alkaliphile
alkaloid
alkalosis
alkanes
alkenes
Al-Khowarizmi (c.780–850)
alkyd
alkyl group
alkyl halide
alkylation
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
almost perfect number
Alnair (Alpha Gruis)
Alnath (Beta Tauri)
Alnilam (Epsilon Orionis)
Alnitak (Zeta Orionis)
alopecia
ALOS (Advanced Land Observing Satellite)
Alouette
alp
Alpha Centauri
Alpha Cygni star
alpha particle
alpha-1 antitrypsin deficiency
Alpha2 Canum Venaticorum star
alphamagic square
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
alternate mission
alternating current
ALTERNATIVE FORMS OF LIFE
altimeter
altitude
altitude sickness
Aludra (Eta Canis Majoris)
alum
alumina
aluminum
aluminum, powdered
aluminizing
Alvarez, Luis Walter (1911–1988)
alveolus
Alzheimer's disease
AM Canum Venaticorum star
AM Herculis star
Am star
amalgam
Amalthea
Amazonian epoch
Ambartsumian, Viktor Amazaspovich (1908–1996)
Ambartsumian's Knot
amber
ambient condition
ambiguous figure
ambipolar diffusion
AMC
American Astronautical Society (AAS)
American Astronomical Society (AAS)
American Institute of Aeronautics and Astronautics (AIAA)
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
ammonium perchlorate (NH4ClO4)
amnesia
amniocentesis
amnion
amniotic fluid
amniotic sac
amoeba
amoeboid
Amor group
amorphous
amorphous semiconductor
amount of substance
AMP (adenosine monophosphate)
Ampère, André Marie (1775–1836)
ampere
amphibian
amphibole
amphipod
amphoteric
amplifier
amplitude
amplitude modulation
AMPTE (Active Magnetosphere Particle Tracer Explorer)
AMS (Alpha Magnetic Spectrometer)
amygdala
amyl alcohol
amyl compound
amylase
amyloid
amyloidosis
amyotrophic lateral sclerosis
anabiosis
anabolism
anacoustic zone
anaerobe
anaerobic
anagram
analemma
analgesic
anallagmatic curve
analog computer
analog device
analog signal
analog-to-digital converter
analogous
analogy, argument from
analysis
ANALYTICAL CHEMISTRY
analytical geometry
ANALYTICAL GEOMETRY
analytical number theory
anamorphosis
Ananke
anaphase
anaphylaxis
anaplasmosis
anastigmat(ic)
anastomosis
anatomical position
"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 astronaut hypothesis
ancient philosophy, related to the possibility of extraterrestrial life
andalusite
Anders, William Alison (1933–)
Anderson, Carl David (1905–1991)
andesite
Andřya Rocket Range
Andrews Air Force Base
androecium
androgen
android
Andromeda (constellation)
Andromeda Galaxy (M31, NGC 224)
Andromedids
andromonoecious
anechoic chamber
anemia
anemic spiral galaxy
anemometer
anemophily
anencephaly
anergolic propellant
anesthesia
aneurysm
Angara
Angelina (minor planet 64)
angina
angiography
angioplasty
angiosperm
angiotensin
angle
angle of attack
angle of incidence
angle of reflection
angle of refraction
anglesite
Anglo-Australian Observatory
Anglo-Australian Planet Search
Anglo-Australian Telescope
angrite
angstrom (Å)
Ångström, Anders Jonas (1814–1874)
angular acceleration
angular diameter
angular momentum
angular momentum quantum number
angular separation
angular velocity
anhydride
anhydrite
anhydrobiosis
anhydrous
ANI
Anik
aniline (C6H5NH2)
animal
animal behavior
animal cell
animal model
animals in space
animals' mathematical ability
animism
anion
anisotropy
ankle
ankylosis
annealing
Annelida (true worms)
annihilation
annual (plant)
annual ring
annual variation
annulus
anode
anodizing
anomalous X-ray pulsar (AXP)
anomaly
anorexia nervosa
anorthite
anorthosite
anoxia
ANRO
ANS (Astronomische Nederlandse Satelliet)
ansa
Ansari X-prize
Ansbro, Eamonn
ant
Ant Nebula (Menzel 3)
antacid
antagonist
Antarctic Dry Valleys
Antarctic Search for Meteorites (ANSMET)
Antares (Alpha Scorpii)
antenna (physics)
antenna (zoology)
antenna array
antenna directivity
antenna temperature
Antennae (NGC 4038 and NGC 4039)
anterior
anterior facial vein
anther
antheridium
anthocyanin
Anthony, Piers (1934–)
anthracene
anthracite
anthraquinone
anthrax
anthro-, anthropo-
anthropic principle
anthropogenic
anthropoid
anthropoid apes
anthropology
ANTHROPOLOGY
anthropomorphic
anthropomorphism
antibiotic
antibody
anticline
anticoagulant
anticodon
anticyclone
antidepressant
antidiuretic hormone (ADH)
anti-g suit
antigen
antigravity
antigravity houses and hills
antihistamine
Antikythera Mechanism
antimagic square
antimatter
antimatter propulsion
antimatter-driven sail
antimony
antinode
Antiope (minor planet 90)
antioxidant
antiparticles
antiphospholipid antibody syndrome
antiprism
antisense
antiseptic
antisolar point
antitail
antitoxin
antlerite
antlers
Antlia (constellation)
Antlia Dwarf Galaxy
Antoniadi, Eugene Michael (1870–1944)
Antoniadi scale
Anura
anus
AO Cassiopeiae
aorta
aortic dissection
aortic valve
aortography
Ap star
Apache Point Observatory (APO)
apastron
apatite
ape
apergy
aperiodic tiling
aperture
aperture synthesis
Apéry's constant
apex (astronomy)
apex (mathematics)
APEX (Athena Precursor Experiment)
aphasia
aphelion
aphid
apical meristem
aplastic anemia
apoapsis
apochromatic
apocrine gland
Apoda
apogee
apogee kick motor
apohele
Apollo (minor planet 1862)
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)
Apollonius problem
Apollo-Soyuz Test Project
apolune
aponeurosis
Apophis (minor planet 99942)
apoptosis
apostilb (asb)
apothecaries' weights
apothem
apotome
apparent horizon
apparent magnitude
apparition
appendicitis
appendix
Appleton, Edward Victor (1892–1965)
applied mathematics
approximation
APPROXIMATIONS AND AVERAGES
appulse
APRO
apsis
Apus (constellation)
Aqua
aqua regia
aqualung
Aquarids
Aquarius (constellation)
Aquarius (spacecraft)
Aquarius Dwarf
aqueous humor
aqueous solution
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
arboreal
arc
arc lamp
Arcetri Astrophysical Observatory
arch
archaea
archaeobacteria
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
arc-second
Arcturus (Alpha Bootis)
area
area codes
Area 51
area rule
Arecibo message
Arecibo Observatory
Arecibo radio telescope
arenaceous
Arend-Roland, Comet (C/1956 R1)
areobiology
areography
areolar tissue
Ares (launch vehicles)
Ares Vallis
arète
Argand burner
Argand diagram
Argelander, Friedrich Wilhelm August (1799–1875)
argentite
argillaceous
arginine
Argo Navis
argon
ARGOS (Advanced Research and Global Observation Satellite)
argument
Argument from Design
argument of perihelion
Argus, Project
Argus radio telescope
Ariane
Arianespace
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 logic unit (ALU)
arithmetic mean
arithmetic sequence
Arizona Search for Planets
ark, interstellar
Arkhipov, Alexey V. (1959–)
arkose
Arkwright, Richard (1732–1792)
armature
armillary sphere
Armstrong, Neil Alden (1930–2012)
Army Ballistic Missile Agency (ABMA)
Arnold, Henry H. (Hap) (1886–1950)
Arnold, Kenneth (1915–1984)
aromatic compound
Arouet, Francois-Marie (1694–1778)
Around the Moon
Arp, Halton Christian (1927–)
array
Arrest, Heinrich Ludwig d' (1822–1875)
Arrhenius, Gustaf
Arrhenius, Svante August (1859–1927)
arrow of time
Arrow paradox
arrhythmias
arsenic
arsenic-based life
arsenopyrite
ARTEMIS (Advanced Relay Technology Mission)
Artemis Project, The
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 the Elder (AD 476–c. 550)
Aryabhata (satellite)
aryl group
arytenoid cartilages
Arzachel (Al-Zarqali, Abu Ishaq Ibrahim ibn Yahya) (1028–1087)
ASAT (antisatellite)
asbestos
Asperger syndrome
Asbolus (minor planet 8405)
ASCA
ascariasis
ascending node
ascending pharyngeal artery
ASCII
Asclepius (minor planet 4581)
Ascomycetes
asepsis
aseptic
asexual reproduction
ash
ashen light
ASI (Agenzia Spaziale Italiano)
Asiago Astrophysical Observatory
Asimov, Isaac (1920–1992)
ASLV (Advanced Satellite Launch Vehicle)
asparagine
aspartame
aspartic acid
aspect
aspect ratio
asphalt
asphyxia
aspirin
assay
assaying
assembly language
ASSET (Aerothermodynamic Elastic Structural Systems Environmental Tests)
assimilation
associationism
associations, stellar
associative
astatine
asterism
Asterix
asteroid
asteroid belt
asteroid mining
Asteroidea
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- (prefix)
Astro- (Japanese satellites)
Astro-E
Astro-F
ASTROBIOLOGY
astrobiology
Astrobiology Institute
astrobleme
astrochemistry
astrocyte
astrodynamics
astroengineering
Astrographic Catalogue
astroid
astrolabe
astrometric binary
astrometry
Astron
astronaut
astronautics
ASTRONAUTS AND COSMONAUTS
Astronomer Royal
ASTRONOMERS AND ASTROPHYSICISTS
Astronomical Almanac
ASTRONOMICAL CATALOGUES
astronomical clock
astronomical constants
astronomical extinction
Astronomical Nulling Interferometer (ANI)
ASTRONOMICAL QUANTITIES
Astronomical Society of the Pacific (ASP)
astronomical unit
Astronomische Gesellschaft Katalog (AGK)
astronomy
astrophotography
astrophysics
astroseismology
astrosociology
Asuka
asymmetric carbon atom
asymmetric drift
asymptote
asymptotic freedom
asymptotic giant branch
A.T. (Aerial Target)
ATA
Atacama Large Millimeter Array
atavism
ataxia
ataxite
Atchley, Jr., Dana W.
Aten group
Athena
Athena (launch vehicle)
Athena Precursor Experiment (APEX)
atherosclerosis
athlete's foot
ATIC
Atiyah, Michael Francis (1929–)
Atlantic Missile Range
Atlantis (Shuttle orbiter)
Atlantis, legend of
Atlas (launch vehicle)
Atlas (moon)
ATLAS particle detector
atmosphere
atmosphere (unit)
atmospheric braking
atmospheric circulation
atmospheric extinction
atmospheric halo
ATMOSPHERIC PHENOMENA AND STRUCTURES
atmospheric pressure
atmospheric refraction
atmospheric trajectory
atmospheric window
ATNF
atoll
atom
ATOMIC AND NUCLEAR PHYSICS
atomic clock
atomic force microscope
atomic mass
atomic mass unit
atomic number
atomic orbital
atomic theory of matter
atomic volume
atomicity
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
attitude control
attitude jets
attractor
attrition
AU
Aubel's theorem
aubrite
auditory canal
auditory nerve
auditory ossicles
Auger, Pierre Victor (1899–1993)
Auger effect
augite
augmentor
Augustine, Norman R. (1935–)
Aura
auricle
Auriga (constellation)
aurora
auscultation
Australian National Radio Observatory
Australian Space Research Institute
Australia Telescope National Facility (ATNF)
australopithecine
autism
autocatalysis
autoclave
autogyro
auto-igniting propellant
auto-ignition temperature
autoimmune disease
autoimmune lymphoproliferative syndrome (ALPS)
autolysis
automated external defibrillator
Automated Transfer Vehicle
automation
automobile
automorphic number
automorphism
autonomic nervous system
autopilot
autopoeisis
autosomal dominant
autosomal recessive
autosome
autotrophs
auxin
avalanche
Averroës (1126–1198)
Avogadro, Amedeo (1776–1856)
Avdeyev, Sergei (1956–)
average
average thrust
averted vision
AVIATION PIONEERS
avionics
Avior (Epsilon Carinae)
Avogadro constant
avoidupois
Avrocar
Axelrod, Julius (1912–2004)
axial period
axial rotation
axil
axilla
axillary artery
axillary vein
axis
axis of symmetry
axiom
axiom of choice
axiomatic method
axion
axolotl
axon
azeotropic mixture
azimuth
azimuthal quantum number
azo compound
azathioprine
Azur
azurite