Glossary
Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the '#' link.
absorbed: Light that is not reflected.
amplitude: Height or amount of energy carried by a wave
brightness: The total amount of light.
camera obscura: A darkened enclosure where light passes through a lens pinhole and an upside-down image is seen on the opposite surface.
chemical energy: Energy that is the result of a chemical reaction or chemical change.
chromatography: A way of separating different coloured substances in a liquid
colour blind: A condition where a person cannot tell the difference between two or more colours, for example red and greed. It is more common in boys than girls.
colour spectrum: the rainbow of colours resulting from white light passing through a prism (red, orange, yellow, green, blue, indigo, and violet).
complimentary light colours: magenta, cyan, and yellow
compressional wave: a wave that moves in the same direction as the periodic motion of the medium
concave: 1. Hollow and curving inward. 2. Curving inward like a cave or the inside of a spoon.
cones: The three types of colour receptors in the eye.
converg(ing): 1. Focusing to a point. 2. Light rays that are bent toward each other; this usually happens with a convex lens.
convex: 1. Curving outward. 2. Curving outward like a ball.
cornea: Transparent part of the eye. It is curved and bends light inwards.
cosmic waves: the highest energy waves from beyond Earth's atmosphere
crest: the highest point of a wave
cycle: A single back and forth vibration of a wave
diverging: 1. Spreading out from a point. 2. Light rays that move apart; usually due to a concave lens.
Doppler effect: A change in the frequency of light or sound waves due to the relative movement between the source and the observer
eclipse: An eclipse occurs when one planet stops sunlight from reaching another.
electric circuit: The path of travel for an electric current.
electric energy: The energy created by a flow of electrons.
electromagnetic radiation: 1.The entire arrangement of visible and invisible light waves. 2. Electric and magnetic forces which vibrate at right angles to each other and can travel through space. These include light, radio waves, and infrared and ultraviolet radiation.
electromagnetic spectrum: n. 1) All bands of light and light like energy. 2)The full range of frequencies, from radio waves to gamma waves, that characterizes light.
electromagnetic waves: Another term for light. Light waves are fluctuations of electric and magnetic fields in space.
energy: The ability to change something or do work.
farsighted: Seeing only far away objects clearly.
fibre optics: 1.A way of sending light along very thin glass fibers. 2. Transfer of light through long, flexible glass or plastic fibers.
fluorescent: 1. Absorbing light energy and then releasing it almost immediately. 2.A short-lived glow of light not caused by high temperature.
focus: The point at which light rays come together to form a sharp, clear image.
frequency: 1. number of crests or troughs that pass a point in a given amount of time (velocity divided by wavelength (velocity divided by wavelength). 2.A property of a wave that describes how many wave patterns or cycles pass by in a period of time. Frequency is often measured in Hertz (Hz), where a wave with a frequency of 1 Hz will pass by at 1 cycle per second.
gamma rays: short, penetrating, high-energy wavelengths emitted by radioactive substances
hologram - A ghostlike, three-dimensional picture normally produced by a laser.
image: The "picture" of an object produced by a mirror or a lens.
infrared: invisible light with wavelengths longer than red.
iris: The coloured part of they eye. Makes the size of the pupil change sizes, depending on the amount of light it lets in.
laser: 1. Light amplification by stimulated emissions of radiation..2.A machine that can produce a narrow, powerful beam of light of one particular wavelength. The word "lase" stands for Light Amplification by Stimulated Emission of Radiation.
laser light: A very intense beam of light of one colour made by putting energy into a material.
lens: 1. A piece of glass that refract light; 2. A transparent part of the eye that focuses an image on the retina.3. A piece of transparent material with curved surfaces that bends or refracts light.
light: A form of energy that stimulates the eye and makes it possible to see things.
light source: Any object that gives off its own light, natural or artificial (the sun, stars, incandescent lights)
light technology: modern use of fiber optics, lasers, and holograms for light
light-year: The distance light travels in one year.
longitudinal wave: see compression wave
luminous: objects that give off or reflect glowing or suffused light
magnify: Make an image appear bigger.
mirage: 1. A mirage is something that you see that isn't really there. 2. An optical illusion, as of a ship in air, or of an oasis in the desert: the image seen in the air generally appears inverted: the phenomenon is due to the reflection of light through two layers of air of different temperature. Light is reflected from a far away object, and refracted into your eyes.
nearsighted: Seeing only items that are close clearly.
nuclear energy: Energy produced by particles such as those in the sun.
opaque: Not allowing light to pass through.
optic nerve: A long, stringlike structure that carries electrical messages from the back of the eye to the brain.
particle: A piece or small bit of matter.
periscope: A device with two mirrors to help you see around corners.
phosphorescent: Glowing after the light source has been removed.
photon(s): 1. The smallest particle of light energy. 2. Light thought of as tiny, massless bundles of radiation energy.
photosynthesis: 1.The process by which plants use the sun's energy to make their own food. 2. The food making process that plants use to change light energy to chemical energy.
pigment: Any substance that gives colour to plant or animal cells or can be ground up to a powder to colour paints or dyes.
primary colour: A colour which cannot be made by mixing other colours.
primary colours of pigment: Yellow, cyan, and magenta (yellow, light blue, and light purple)
primary light colours: 1. Red, green, and blue. 2. A colour which cannot be made by mixing other colours. The primary colours of light are red, green and blue. The primary colours of pigments are yellow, cyan and magenta. All other colours can be made by mixing the primary colours.
prism: 1. A solid transparent shape usually made of glass, which can be used to separate the colours in visible light. 2. A block of glass or plastic that separates white light into the colours of the visible spectrum.
pupil: The pupil is the black opening in the coloured part of the eye. Light passes through this opening.
radiant energy: Energy that is derived by heat.
radiation: The carrying of energy by waves. These waves are part of the electromagnetic spectrum.
radio waves: A form of light with a frequency that is much lower than visual Light.
rarefaction: Low pressure region in a compressional wave
reflect: To throw or bounce back.
reflection: 1. The bouncing back of light from a surface. 2. Waves that strike and bounce off an object. 3. When light bounces off a surface we say it is reflected. Everything reflects some light.
refract: To cause a change in direction of a ray of light so that it appears to bend.
refraction: 1. The bending of light when it passes from one transparent substance to another.2. Bending of waves due to a change in a medium
retina: The layer at the back of the eye that is sensitive to light. It contains rods and cones which are connected to the brain through the optic nerve.
solar water heater: A water heater powered by energy from the sun.
spectral line: Light given off at a specific frequency by an atom or molecule. Every different type of atom or molecule. Every different type of atom or molecule gives off light at its own unique set of frequencies; thus astronomers can look for gas containing a particular atom or molecule by tuning the telescope to one of its characteristic frequencies. For example, carbon monoxide has a spectral line at 115 GigaHertz (or a wave length of 2.7 mm).
spectrum: A plot of the intensity of light at different frequencies.
speed of light: In air, light travels at 300,000 million kilometers per second (186,000 million miles per second), which is over 500,000 times faster than the Concorde. In solids or liquids, light travels more slowly.
transmit: To allow to pass through.
translucent: Allowing light, but not images, to pass through.
transverse wave: any wave in which the medium moves at right angles to the wave direction.
trough: the lowest point of a wave
ultraviolet: invisible light with wavelengths shorter than violet
velocity: speed at which an object travels
visible light: 1. Any part of the electromagnetic spectrum visible to the human eye. 2. The entire colour spectrum; the only light we can see.
visible spectrum: The bands of colored light that appear when white light is passes through a prism.
wave: 1. A disturbance that travels through matter or space. 2. A way in which energy moves from one place to another.
waveband: Portions of the electromagnetic spectrum. Examples of different wavebands include the infrared, visual, radio wavebands.
wavelength - 1.A property of a wave that gives the length between two peaks of the wave. 2.The length between identical points on two waves next to each other. Each type of electromagnetic radiation has a different wavelength. 3. Distance between consecutive crests or troughs. 3. Each type of radiation has a different wavelength.
wave speed: Wavelength times wave frequency.
white light: All frequencies of visible light come together to form white light.
X ray: 1. Very short light rays from the electromagnetic spectrum used in medical photography.