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Altazimuth (Alt-Az) mount - is a simple two-axis telescope mount for supporting and rotating an instrument. There are both advantages and disadvantages to this type of mount compared to an Equitorial (EQ) mount.
Arc-minute - is a unit of angular measurement used to describe the apparent size of an object, and is equal to 1/60 of one degree. To the naked eye, a normal full moon is about 30 arc-minutes or 0.5 degrees in size.
Asterism - is a pattern of stars we recognized in Earth's night sky. It may form part of a constellation, or be composed of stars from more than one.
Asteroids - are chunks of rock made up of metals and other material, and tend to have circular orbits round the Sun. If they enter Earth's atmosphere then we call them meteors.
Astronomical Unit (AU) - is a unit of measure equal to the average distance between the Earth and the Sun (93 million miles).
Aurora Borealis (northern lights) - this is an atmospheric phenomenon caused by charged particles from the Sun as they interact with the Earth's magnetic field at the poles, causing curtains of light in the sky.
Big Bang – is the theory that suggests that the universe was formed from a single point in space during a cataclysmic explosion about 13.7 billion years ago.
Black holes - are regions of space having intense gravitational fields so no matter or radiation can escape. There is a super massive black hole at the centre of our galaxy.
Celestial equator - is the great circle of the imaginary projection of the Earth's equator out onto the observers night sky.
Collimation - is the process of aligning the optical elements of a telescope so that they all point in the proper direction.
Comets - are made up of ice, dust and rocky material, and have long extended orbits.
Constellation - is a specific area of the night sky containing a number of stars - this area is defined by the International Astronomical Union (IAU).
Deep sky objects - are basically everything outside our solar system (so not the Sun, Moon, planets, comets). Often faint naked eye and telescopic objects such as star clusters, nebulae and galaxies.
Dobsonian or Dob telescope - a type of Newtonian reflector, made popular by amateur astronomer John Dobson, often made with a wooden mount.
Ecliptic - the great circle that is the apparent path of the Sun among the constellations in the course of a year.
Electromagnetic radiation (EMR) - consists of waves of the electromagnetic field. Types of EMR include radio waves, microwaves, infrared, (visible) light, ultraviolet, X-rays, and gamma rays, all of which are part of the electromagnetic spectrum.
Equinox - twice each year at the Earth’s equator the Sun is directly overhead at noon, so day and night are of equal length.
Equitorial (EQ) mount - is a telescope mount that allows a telescope to track objects across the sky with minimum effort.
Focal length - is the length of an optical system, such as a telescope, from objective lens or mirror to the point of focus.
Focal ratio (f-number) - is a measure of the light-gathering ability of an optical system such as a telescope. It is calculated by dividing the system's focal length by the diameter of the objective lens or mirror.
Galaxy - is a massive, gravitationally bound system consisting of stars, and other debris. There are about 100 billion galaxies in the observable universe.
Gravitational Lens – is an optical phenomenon. A large galaxy or cluster of galaxies bends light rays from an object behind. This results in duplicate images of these distant objects.
Infrared light (IR) - is electromagnetic radiation with wavelengths longer than that of visible light but shorter than microwaves. Infrared is outside the visible light spectrum, so it is invisible to the human eye, but can be felt or detected as heat. IR is generally understood to include wavelengths from around 750 nm to 1000 μm.
Light or visible light - is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm).
Light speed or speed of light - is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second.
Light-year - the distance that light travels in one year is 9.46 trillion kilometers or 5.88 trillion miles.
Magnitude – is a number denoting the brightness of a star or other celestial object. The higher the magnitude number, the fainter the object.
Meridian - is the great circle passing through the celestial poles.
Meteor – is the visible passage of a meteoroid, comet, or asteroid entering Earth's atmosphere.
Meteorites – are meteors that pass though the atmosphere and hit the ground.
Meteoroid - is a small rocky or metallic body in outer space. Meteoroids are distinguished as objects significantly smaller than asteroids, ranging in size from grains to objects up to a meter wide.
Nebula, Nebulosity - a cloud of gas and dust in outer space, visible in the night sky either as an indistinct bright patch or as a dark silhouette against other luminous matter.
Parsec - is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years.
Protoplanetary disk - is a rotating disc of dense gas and dust surrounding a young newly formed star (Protostar), and which may be an early stage in the formation of planets.
Protostar - is a very young star that is still gathering mass from its parent molecular cloud. This is the earliest phase in the process of stellar evolution.
Reflector telescope - is a telescope that uses a single or a combination of curved mirrors that reflect light and form an image. The Hubble space telescope is a large example of a reflector telescope.
Refractor telescope - is a type of optical telescope that uses a lens as its objective to form an image. The refracting telescope design was originally used in spyglasses and astronomical telescopes but is also used for long-focus camera lenses.
Seeing - a measure of the atmosphere’s stability. Poor seeing makes objects waver or blur when viewed in a telescope at high magnification.
Solar System - describes a star and all the objects that travel in orbit around it. Our solar system consists of the sun, our star and eight planets, moons, asteroids and comets.
Stars - are a balls of very hot gas. Our sun is the star at the centre of the Solar System. There about 100 billion stars in our own Galaxy - the Milky Way.
Supernova - A star ending its life in a huge explosion. In comparison, a nova is a star that explosively sheds its outer layers without destroying itself.
Telescope - is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation.
Wavelength of light - the distance between two adjacent crests or troughs of an electromagnetic wave.
Zenith - is an imaginary point directly "above" a particular location, on the celestial sphere.
