Glossary

  • Adaptive optics: a technique that corrects for image deformations caused by turbulence. In astronomy, the terrestrial atmosphere produces turbulence, and one of the observed effects is the twinkling of stars.
  • Asteroid: an irregularly shaped celestial body made of rock and metal having a diameter of more than 100 metres.
  • Astrology: the non-scientific study of the influence of celestial objects on terrestrial events.
  • Astronomy: the scientific study of celestial objects (for example galaxies, stars and planets), their positions, sizes, movements, relative distances, compositions, physical conditions, interactions, and histories.
  • Astrophysics: the scientific study of the physics of the Universe and the physical properties of their constituents (luminosity, temperature, chemical composition).
  • Asteroseismology: the scientific study of the vibrations that shake stars. The vibrations provide information about the internal structure of stars, and thus about their size, mass and constituents.
  • Atom: the smallest component of a chemical element. Linked together, atoms form molecules.
  • Big Bang: the phenomenon responsible for the creation of the Universe. The Big Bang is often compared to a giant explosion that caused the Universe to expand from a very hot and dense single point. Space, time, light and matter were created by the Big Bang.
  • Binary star: a pair of stars linked by gravitational force (an attractive force) in such a way that one star revolves around the other.
  • Black hole: a celestial body that is so massive and dense that nothing can escape its gravitational pull (attractive force), not even light.
  • Blue star: a very bright star that generates a great amount of ultraviolet light. Its surface temperature is at least 25,000 °C.
  • CCD: abbreviation for “charge couple device” – a circuit made from photosensitive cells that is used to take digital photographs. A CCD consists of a thin silicon layer divided into a multitude of small squares called pixels (short for picture element).
  • Comet: a celestial object consisting of a mixture of ice, rock and metal.
  • Électron: eerie light emitted several hundred thousand years after the birth of the Universe when the first atoms were created. Cosmic background radiation represents 99.9 % of all the light energy in the Universe; the remainder (0.1%) represents light from stars.
  • Cosmology: the scientific study of the origin and evolution of the Universe as a whole.
  • Doppler imaging: a technique for taking images using the shift of a star’s spectral lines towards the red spectrum.
  • Eclipse: the phenomenon that occurs when one celestial object, such as a planet or natural satellite (like the Moon, for example), is hidden behind another (the Sun, for example).
  • Electromagnetic spectrum: the entire range of light waves arranged according to their wavelength or the energy of their photons.
  • Electromagnetic waves: energy that propagates as a wave and is produced by the movement of electrical charges.
  • Electricity: a form of energy produced by the movement of electrically charged particles, like electrons (negative charge) or protons (positive charge).
  • Electron: an elementary (subatomic) particle with a negative electrical charge and negligible mass.
  • Emission line: a bright line in the electromagnetic spectrum generated by a hot luminous body.
  • Galaxy: a celestial object comprising millions of stars, gas and dust held together by the force of gravity (an attractive force). The components of a galaxy all revolve about a common point. Our galaxy is known as the Milky Way.
  • Globular cluster: a spherical collection of anywhere from 10,000 to several million stars.
  • Gravitational lens: an astronomical phenomenon created when a very large celestial body aligned between Earth and a more distant object causes light from the distant object to bend around it, much like a lens bends light, resulting in a doubling of the distant object’s image when viewed from Earth.
  • Interferometer: an instrument that combines the collected light rays at the exit point of a telescope to reinforce (or minimize) specific light waves; one of its uses is to improve the image.
  • Interstellar space: the space between stars.
  • Laser: the abbreviation for “light amplification by stimulated emission of radiation”. It consists of a device that amplifies light to create a concentrated (narrow) beam.
  • Latitude: a coordinate system that describes a position on Earth’s surface north or south of the equator. It is expressed in the form of an angle that increases from 0° at the equator to 90° at the North and South poles.
  • Light-year: a unit of distance representing the distance travelled by light in one year; that is, 9,460 billion 730 million 472 thousand and 581 kilometres (approximately 10,000 billion kilometres). The speed of light is about 300,000 kilometres per second.
  • Longitude: a coordinate system that describes a position on the Earth’s surface east or west of an imaginary line known as the Prime Meridian, which passes through the town of Greenwich, England. Latitude is expressed as an angle from 0° at the Prime Meridian to 180° at the International Date Line in the Pacific Ocean.
  • Magnétisme: the force of nature produced by the movement of charged electrical particles like electrons.
  • Météore: a light phenomenon caused by the combustion of a celestial object as it enters a planet’s atmosphere. Synonym: shooting star.
  • Météorite: a fragment of a foreign celestial body found on the surface of a planet or a natural satellite.
  • Neutrino: a tiny elementary (subatomic) particle with no electrical charge and very little interaction with matter.
  • Neutron star: a small star consisting mainly of neutrons, which is a type of neutral elementary (subatomic) particle with no electrical charge. A neutron star is typically the remnant of a supernova explosion.
  • OB star: a very hot blue star for which the surface temperature exceeds 11,000 °C.
  • P. Cygni star: a variable supergiant star in the Cygnus constellation. It is our galaxy’s prototype for a Wolf-Rayet star.
  • Photometry: a technique that measures the intensity (brightness) of the light emitted by a celestial object; it provides information about the object’s size, temperature, etc.
  • Photon: a particle of light energy. A photon has no mass and travels approximately 300,000 kilometres every second.
  • Polarimetry: a technique for measuring the orientation and direction of light waves. It provides a wealth of information for studying stellar atmospheres, including that of our Sun, as well as the interstellar medium and nebulas, and for detecting magnetic fields.
  • Quasar: celestial object that, when seen through a telescope, resembles a star although it is actually a very active distant galaxy that emits great amounts of energy. The name quasar is a shortened form of “quasi-star”.
  • Radiation: Energy that is transmitted as waves or particles traveling through space.
  • Radio telescope: an instrument used to collect radio waves emitted by celestial bodies; collection is generally by means of a large parabolic antenna (dish).
  • Spectroscopy: a technique for measuring the properties of the electromagnetic spectrum produced by a substance. In astronomy, for example, it can be used to analyze the emitted light from a celestial object to determine its chemical composition.
  • Star: a massive ball of very hot gas that generates energy by means of nuclear reactions. A typical composition is 98% hydrogen and helium, and 2% heavier elements. See also: binary star, blue star, neutron star, OB star, P. Cygni star, supernova, variable star, white dwarf, and Wolf-Rayet star.
  • Sun spot: a relatively dark and cool region on the Sun’s surface caused by the Sun’s magnetic field.
  • Supernova: an explosion produced when a large star has consumed all its nuclear fuel and collapses in on itself and then bursts outwards
  • Theory of relativity: a fundamental theory of physics initially developed by the German physicist Albert Einstein. It describes the relationship between matter and energy, space and time, and the forces of gravity and acceleration.
  • Variable star: a star that changes in brightness (variable luminosity).
  • White dwarf: a very old star that has consumed its nuclear fuel and is collapsing upon itself. It is small and dim. The Sun will become a white dwarf at the end of its evolution.
  • Wolf-Rayet star: an old, massive and hot type of star discovered in 1867 by the French astronomers Charles Joseph Étienne Wolf and Georges Antoine Pons Rayet.

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