O star
Oak Ridge Observatory
OAO (Orbiting Astronomical Observatory)
oases
OB association
OB stars
obelus
Oberon
Oberth, Hermann Julius (1894-1989)
objective
oblate spheroid
oblique
oblique rotator
obliquity
oblong
oblong number
OBSERVATIONAL ASTRONOMY
Observatoire de Haut-Provence
OBSERVATORIES AND TELESCOPES
obsidian
obtuse
occipital bone
occultation
occulting disk
Ocean Art: the Mediterranean Sea Terrace Proposal
ocean planet
oceans, origin
ocellus
Ockham (Occam), William of (c.1280-1347)
octa-
octagon
octahedrite
octahedron
octane
Octans (constellation)
octant
octonion
octopus eye
oculomotor nerve
odd
ODERACS (Orbital Debris Radar Calibration Sphere)
Ofeq
OFO (Orbiting Frog Otolith)
OGLE
OGLE-2005-BLG-390Lb
OGO (Orbiting Geophysical Observatory)
Ohio SETI Program
Ohio State University Radio Observatory
ohm (unit)
Ohm's law
Ohzora
OICETS (Optical Inter-orbit Communications Engineering Test Satellite)
oil
OKB-1
OKB-52
OKB-586
Okean
Oko
Olbers, Heinrich Wilhelm Matthäus (1758-1840)
Olber's Paradox
old
olfactory nerve
Oligocene epoch
oligomer
oligonucleotide
Oliver, Bernard ("Barney") M. (1916-1995)
olivine
Olympus
Olympus Mons
Omega Centauri
Omega Nebula (M17, NGC 6618)
omnidirectional antenna
oncovirus
one
One Hectare Telescope (1HT)
one-g spacecraft
O'Neill, Gerard Kitchen (1927-1992)
O'Neill-type colony
ONERA (Office National d'Etudes et de Recherches Aérospatiale)
one-to-one (correspondence)
one-way light time (OWLT)
ontogeny
oocyst
oogonium
Oort, Jan Hendrik (1900-1992)
Oort Cloud
Oort Limit
oospore
opacity
OPAL (Orbiting PicoSat Launcher)
Oparin, Aleksandr Ivanovich (1894-1980)
Oparin-Haldane Theory
Opel-RAK
open
open cluster
Operation Paperclip
operator
Ophelia
Ophiuchus (constellation)
Öpik, Ernst Julius (1893-1985)
opinion polls, about extraterrestrials
Oppenheimer-Volkoff limit
opposition
optic disk
optic nerve
optical axis
optical depth
Optical Gravitational Lensing Experiment (OGLE)
optical illusion
optical interferometer
optical SETI
optical SETI at Berkeley
optical SETI at Harvard-Smithsonian
optically violent variable (OVV)
OPTICS AND OPTICAL PHENOMENA
Orbcomm
Orbison's illusion
orbit
orbit (eye)
orbit decay
orbital
orbital airship
orbital curve
orbital cycler
orbital element
orbital energy
orbital loop
orbital migration
orbital muscles
orbital node
orbital period
orbital plane
orbital resonance
orbital rotation
Orbital Sciences Corporation
orbital station-keeping
orbital velocity
orbiter
Orbiter, Project
Orbiting Astronomical Observatory (OAO)
Orbiting Geophysical Observatory (OGO)
Orbiting Solar Observatory (OSO)
OrbView
Orcus (minor planet 90482)
order
ordinal number
ordinary chondrite
ordinary differential equation
ordinate
Ordway, Frederick Ira III (1927-)
Oresme, Nicole
organ
organ of Corti
organ system
organelle
organic
ORGANIC CHEMISTRY
organic chemistry
organic matter, in meteorites
organometallic compound
Orgel, Leslie E. (1927-)
Orgueil meteorite
orientable surface
origami
origin
ORIGIN AND EVOLUTION OF LIFE
Origins Program
Orion (constellation)
Orion (Crew Exploration Vehicle)
Orion, Project
Orion III Pan Am "Space Clipper" (from 2001: A Space Odyssey)
Orion Arm
Orion Complex
Orion Nebula (M42, NGC 1976)
Orion variable
Orion's Belt
Orion's Sword
Orion-type star
Orlets
ornithopter
orrery
Ørsted
orthic triangle
orthocenter
orthoclase
orthogonal
orthopyroxene
orthopyroxenite
OSCAR (Orbiting Satellite for Communication by Amateur Radio)
osculating
osculating orbit
OSETI
osmosis
osteoarthritis
osteomyelitis
Osumi
otitis media
Oughtred, William (1574-1660)
outer ear
Outer Space Treaty of 1967
outgassing
oval
ovary (animal)
ovary plant)
Ovda Regio (Venus)
overcontact binary
overshoot boundary
Ovid's Game
Overwhelmingly Large Telescope (OWL)
overweight and obesity
ovule
ovum
oxalic acid
oxaloacetate
oxidation
oxide
oxidizer
oxidizer-to-fuel ratio
oxidizing
oxygen
oxygen, regenerative
oxygen-hydrocarbon engine
oxytocin
Owens Valley Radio Observatory (OVRO)
Owl Nebula (M97, NGC 3587)
Oyama, Vance I.
Oyama's hypothesis, about active nature of Martian soil
Ozanam, Jacques (1640-1717)
Ozma, Project
ozone
ozone layer