A

abberation - a defect in an optical system
absolute zero - the lowest temperature possible –273.16 ^oC
absorb - take in
absorption spectrum - a spectrum formed by the passage of light through a cooler vapour.
a.c - alternating current, current that continually changes direction
acceleration - the rate of change of speed, change of speed divided by the time taken
accelerator - apparatus for accelerating something, as in a charged particle accelerator
accommodation - ability of the eye to focus on objects at different distances from it
accretion - the capture of matter by a neutron star or black hole usually forming a disc
accumulators - batteries that can be charged, as in lead-acid accumulators used as car batteries
achromatic - lens or prism that corrects for chromatic aberration
acoustics - branch of Physics dealing with sound
activity - of a radioactive source. The number of emissions per second. Unit Becquerel.
adiabatic - changes that take place in a gas without heat energy entering or leaving the gas
adhesion - force of attraction between two unlike materials
AGR - advanced gas-cooled reactor
aerodynamics - the study of the motion of solid objects through air. Basis of flight.
aim - purpose, as in the 'aim of an experiment'
albedo - reflective power of a planet, the fraction of reflected to incident diffuse light
alpha particle - a charged particle emitted in some radioactive decays. Nucleus of a helium atom
alternating - changing direction, as in alternating current (a.c)
alternator - an alternating current generator
altimeter - instrument for measuring height above the ground (altitude)
ammeter - instrument for measuring the size of an electric current
ampere - unit of electric current (shortened to amp (A))
ampere balance - apparatus used to measure the permeability of free space, or the current
amplitude - in a wave, maximum displacement, the distance from the centre to the crest
amplitude modulation - modulation of a signal by a change of its amplitude
analogue signal - constantly varying signal
AND - a type of logic gate. Output high when input A and input B are high
Andromeda nebula - extragalactic nebula, a spiral galaxy, a 'close' neighbour to our galaxy
anechoic - without echo, as in 'anechoic chamber' a room used for studying sounds
anemometer - a piece of apparatus for measuring wind speed
aneroid - type of barometer
angular momentum - momentum of a rotating object (I?)
angle of contact - angle between a liquid surface and a solid; water-glass 0o, mercury-glass 140o
anion - an ion that carries a negative charge and so moves towards the anode
anisotropic - having a property that is different in different directions, e.g. tensile strength
annihilation - process where a particle and its antiparticle meet and are converted into energy
annular eclipse - eclipse of the Sun when the outer layers of the Sun are visible round the Moon
anode - positive electrode
anomalous - unusual, out of the ordinary, does not fit the trend (anomalous points on a graph)
antimatter - material containing similar particles to matter but with opposite charges
antineutrino - particle with no charge and 'zero' mass emitted in beta minus decay
antinode - point of maximum vibration on a standing wave
antiparallel - parallel but pointing in the opposite direction
Appenines - a range of lunar mountains
aperture - in astronomy, the diameter of the objective (lens or mirror) of a telescope
aphelion - the position in the orbit of a planet that is furthest from the Sun
apogee - the position in the orbit of a satellite that is furthest from the Earth
Apollo - mans mission to the Moon in the 1960s and 1970s
apparent depth - the depth an object in a fluid appears to be, apparent depth of a pond
apparent magnitude – the magnitude of a star as seen form Earth
aqueous humour - fluid between the cornea and the lens in the eye
arc - luminous electrical discharge in a gas
Arcturus - bright yellow star in Bootes. Absolute brightness 115 suns.
Ariel - satellite of Uranus. Evidence of considerable past geological activity.
Aristarchus - a very bright lunar carter. Centre of a bright ray system
armature - a rotor in an electric motor made of several coils wound on a soft iron core
astable - a circuit that flips backwards and forwards between two stable states (flip-flop)
asteroid - minor planet, orbiting mainly between Mars and Jupiter
astrolabe - ancient instrument used to measure the altitude of the Sun, stars, and planets
astronautics - the science of space travel
astronomical unit - very nearly equal to the separation of the Earth and the Sun, 149 597 870 km
astrophysics - the physics of astronomy
atom - the smallest particle of any element
atomic mass unit – unit of atomic mass, one twelfth the mass of the carbon 12 atom
atomic number - number of protons in the nucleus. Now called the proton number
attenuation - the reduction in the intensity of radiation due to its passage through matter
aurora - luminous curtain-like discharge in the atmosphere. Seen at best near the poles.
Avogadro's constant – the number of molecules in a mole of any substance. 6.02x1023
axis - a line
axis of rotation - a line about which something rotates (spins)
azimuth - the bearing of an object. Taking north as zero through east, south, west