Arcsecond – A basic angular measure in astronomy equal to 1/3600 of a degree of arc.
Astronomical Unit – The average distance between Earth and Sun equal to 149 million km (92.6 million miles).
Big Bang – The name used to describe the cosmological model based upon Einstein’s theory of general relativity, more properly called the Friedmann-Lemaitre-Robertson-Walker cosmological model
Black hole – An object predicted by general relativity whose spacetime curvature is large enough to prevent light from escaping at a distance from its centre defined by its event horizon.
Black-body spectrum – The unique energy distribution of electromagnetic radiation that occurs when an object is opaque to its own emission so that the electromagnetic energy can thermalize with the matter in the object at a unique temperature.
Boson – A class of fundamental elementary particles that possess an integer unit of quantum spin such as photons, gluons and W and Z particles.
Cannibalism – The physical process by which a system gains mass at the expense of consuming neighbouring gas or other collections of matter such as stars or galaxies.
Cosmic background radiation – The population of photons generated by the events during the Big Bang, which form a gas of photons that permeate all locations within the cosmos.
Cosmological constant – A mathematical quantity added to Einstein’s equation for gravity, which serves to prevent the collapse of matter at cosmological scales. Also called Dark Energy.
Dark energy – A condition of space similar to Einstein’s cosmological constant, which causes the rapid expansion of space.
Dark matter – A ‘substance’ commonly detected in the halos of galaxies or in clusters of galaxies, which does not interact with or generate light but only acts through its gravitational force with other matter.
Degeneracy – A quantum condition involving fermions in which the particles of a plasma occupy all of the available quantum states for the system. An important force for the stability of white dwarfs and neutron stars.
Differential rotation – The manner in which a gaseous sphere attempts to rotate as a solid body, but lacks cohesion so that its equator travels faster than its polar material.
Electromagnetism – The force that acts between charged particles, which has both a magnetic and electrostatic character that changes with the relative speeds of the observers according to special relativity.
Exoplanet – A planet-sized object orbiting another star.
Extremophile – A species of bacterium which can survive under normally lethal conditions of temperature, salinity, or pressure.
Fermion – A class of fundamental elementary particles that possess ½ units of quantum spin such as electrons, neutrinos and quarks.
Field – Any physical quantity that has a distribution in space and can be characterized by unique values (scalar, vector or tensor) at every mathematical point in space.
Frost line – The distance from a star where exposed surfaces are cool enough that liquid water solidifies to snow or ice.
Fusion – The process by which two separate systems, usually nuclei, combine together to form heavier systems, such as three helium nuclei fusing together to form a carbon nucleus.
Galactic halo – The region of space surrounding a galaxy in which are generally found the oldest stars in the system.
Galaxy – A system of stars and interstellar gas that can contain upwards of hundreds of millions of stars, and considered the most elementary constituents of large-scale cosmic structure.
Habitable zone – The region surrounding a star in which temperature and surface conditions allow for water to be found in a liquid state suitable for living systems.
Hyperstar – A star with more than about 50 times the mass of our Sun.
Inflation – A physical process involving the rapid increase in the separations between material objects due to a change in the energy of empty space, called the quantum vacuum.
Interferometer – A telescope design in which pairs of telescopes combine their signals to form a new telescope with an equivalent diameter equal to the separation between the telescopes.
Lepton – An elementary particle of the fermion class which only interacts through the electromagnetic or weak forces such as electrons, muons, tauons and their associated neutrinos.
Light year – The distance travelled by light in one year equal to 9.5 trillion kilometres (5.9 million miles).
Luminosity – The amount of energy, usually in the form of light, emitted by a star each second, usually represented in units of watts or ergs/sec. One solar luminosity (Lsun=1.0) equals 3.8×1026 watts.
Magnetism – A force generated by currents of charged particles which has a handedness or ‘polarity’ commonly referred to as north or south.
Main Sequence – On a Hertzsprung-Russell Diagram, the diagonal band occupied by most stars in the sky, corresponding to the stable burning of hydrogen into helium.
Parallax – The apparent shift in the position of an object as seen from two different vantage points, usually measured in degrees of angle.
Parsec – The distance at which the parallax shift of an object equals 1 arcsecond or 1/3600 of a degree and equal to 206,265 Astronomical Units or 3.26 light years.
Photon – A quantum of electromagnetic energy characterized by its integer-spin (boson) and its wavelength.
Planck Era – A period of time in the history of the universe before about 10-43 seconds after the Big Bang when/where space and time can no longer be described by conventional non-quantum terms.
Planet – A large object that has swept out nearly all of the material in its surroundings and has no other nearby neighbours. Pluto is not a planet because it is still embedded in a significant debris field called the Kuiper Belt.
Planetesimal – A class of massive objects that are still accreting material from their surroundings during the planet-forming era in a solar system, typically about 500–1000 km (310–621 miles) in diameter.
Plasma – A collection of particles consisting of electrons, protons and the ionized versions of various atoms. Highly reactive to magnetic fields and exists at temperatures above 10,000 kelvins.
Primordial elements – The small collection of elements which could have formed soon after the Big Bang, consisting of hydrogen, deuterium, helium, tritium, lithium and beryllium.
Protostar – A large object forming at the centre of a disk of gas and dust into which matter is still in-falling and will eventually collapse to form a star.
Pulsar – A rapidly rotating neutron that emits bursts of radio energy in beams which can sweep across the direction of Earth and cause periodic radio signals.
Quark – An elementary particle of the fermion class which exists within larger particles called protons and neutrons, and which are held together by the strong force mediated by bosons called gluons.
Quasar – A distant galaxy in which a supermassive black hole is rapidly consuming matter and generating a luminosity equal to hundreds of Milky Way galaxies.
Radiation – The outflow of particles or energy from a source in space, which decreases in intensity according to the inverse-square law.
Spacetime – A mathematical concept in which the three dimensions of space and the one dimension of time are combined into a four-dimensional geometry within which all events in the cosmos occur along individual worldlines.
Spin network – In quantum gravity theory, a collection of points connected by relationships such that the point occupies a Planck volume in space, and the point-to-point relationships are represented as connecting line segments that carry a quantum of surface area.
Supercluster – A collection of hundreds of clusters of individual galaxies that travel through the universe as a single system.
Superstring – A one-dimensional loop of spacetime whose vibrations in 10 dimensions provide the properties of the individual particles and their interactions.
Tachocline – The region in the solar interior between the radiative and convective zones where plasma currents can form that generate the solar magnetic field.
Telerobotics – The technology that allows robotic systems such as rovers to be operated millions of miles away by humans.
The Bulk – The name given to the 11-dimensional spacetime in which our four-dimensional spacetime is embedded in a structure called a brane.
T-Tauri –A phase in the formation of a star characterized by the last stages in the accretion of matter onto the surface of a star including magnetic fields, which cause enormous flares and plasma ejection events.
Unification – The approach to elementary particle physics that says that there is a single comprehensive mathematical model that accounts for the properties of particles and the forces through which they interact.
Vacuum energy – Quantum mechanics requires that the vacuum be filled with a variety of ‘virtual particles’, and these particles and fields contribute to the vacuum having a definite non-zero energy.
Worldline – The three-dimensional locations of a particle connected in time form a four-dimensional line called the worldline, which starts at the birth of the particle and ends when the particle vanishes in the future.