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A glossary of science-related words.

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A method of detecting distant objects and determining their position, speed, or other characteristics by using very high frequency radio waves reflected from the objects’ surfaces.

radial velocity

The speed of something as it moves directly towards, or away from, an observer.

radiant energy

Energy transferred by radiation, especially by an electromagnetic wave.


Energy that is transmitted (radiates) from a source in the form of rays or waves or particles.

radio telemetry

The process by which information is gathered and recorded at a distance. In the case of rocket tracking, electronic equipment on board the tracked rocket collects and processes various data and then relays this data as an encoded signal to receiving stations (rocket tracking stations) back on Earth. The data is then decoded, recorded and analyzed. Examples of some of the forms of data collected include location, altitude, attitude, engineering data and hull conditions.

radio waves

An electromagnetic wave having a wavelength between 1 millimetre and 30 000 metres. Radio waves are used for transmitting radio and television signals. Many celestial objects, such as pulsars, emit radio waves.


Giving off energy as a result of the breaking up of nuclei of atoms. Something undergoing radioactive decay, the process by which an unstable atom emits radiation.

radioactive decay

The process in which an unstable atomic nucleus loses energy by emitting radiation. This decay, or loss of energy, results in an atom of one type, called the parent nuclide, transforming to an atom of a different type, called the daughter nuclide. The average time interval required for one-half of any quantity of identical radioactive atoms to undergo radioactive decay is called half life.


The spontaneous emission of radiation from an atom’s nucleus.

radiocarbon dating

Working out the approximate age of an old object, such as bones or seeds, by measuring the amount of carbon 14 (C-14) it contains. When an organism dies, it no longer absorbs C-14 from the world around it. The C-14 it does contain in its tissues then starts to decay at a constant rate (half-life of 5730 ±40 years). An estimate of the date at which an organism died can be made by measuring the amount of C-14 left.


An atom with an unstable nucleus. The excess energy associated with the nucleus is released when the nucleus undergoes radioactive decay.


A person specially trained to diagnose diseases of the human body using x-rays, ultrasound, magnetic resonance imaging (MRI), computed tomography (CT), which gives cross sections of internal body parts, and nuclear medicine – the injection and tracking of radioactive solution in the body.

radiometric dating

A range of techniques that use the decay of radioactive elements to date some materials. Examples include radiocarbon, potassium-argon and fission track dating.


A Māori word meaning to restrict access to or use of an area or resource by unauthorised persons.


When the sun shines on tiny droplets of moisture in the Earth’s atmosphere, a spectrum of light (the colours of the rainbow) appears in the sky in the form of a single arc.

randomised controlled trial

A scientific study in which people are allocated at random to either receive a clinical intervention (an active pill or other intervention) or not (a placebo or no intervention at all – also called the control group).

rare-earth metals

A group of reactive, often toxic, metal elements, also called lanthanides. One use is in supermagnets.

rare-earth nitride

A chemical made of a rare-earth metal and nitrogen, which is being investigated as a semiconductor.

Rayleigh scattering of light

The reflection of light by very small particles that are smaller than the wavelength of light. This type of scattering causes the blue colour of the daytime sky, the reddening of the Sun at sunset and the yellow colour of the Sun.


A substance used in a laboratory to produce a reaction.

reassortant strain

A strain produced from the genetic material of two or more similar viruses. An example of a reassortant strain is H1N1 (swine flu), which is a combination of swine flu, bird flu and human flu.


The end portion of the large intestine, about 12 cm long in humans, that temporarily stores faeces prior to egestion.

red giant

A star of great size and brightness that has a relatively low surface temperature. A stage in the life of a star.

red sprite

A large-scale electrical discharge that occurs between the top of a thunderstorm cloud and the upper atmosphere. Triggered by lightning discharges between the cloud and the ground, they have a fleeting appearance as red luminous flashes.


The bouncing back or deflection of waves as they hit a surface.


The bending of a wave as it passes from one medium to another. Refraction signifies a change in velocity (speed) of the wave.


Pipes, tubes, conduits and bricks used in furnaces, kilns, incinerators and reactors. The refractory materials used to make them have to be chemically inert, resistant to thermal shock and durable.


A fluid that acts as the heat carrier in the heating cycle of a heat pump or cooling cycle of a refrigerator. It is also known as the ‘working fluid’. 


The process of ecological restoration, which provides conditions to build up populations of native flora and fauna.

relative dating

Putting a series of events or objects, such as rock layers, in chronological order, but does not include actual dates.

relative humidity

The ratio of the amount of water vapour in a given parcel of air, at a set temperature and pressure, to the maximum amount that the parcel of air could hold under the same conditions. It is expressed as a percentage.


Make an exact copy of.


A class of animals that includes snakes, lizards, alligators, crocodiles, tortoises and turtles.


1. A natural or artificial structure that stores water. 2. An underground accumulation of natural gas or petroleum oil.


A solid or liquid synthetic organic polymer used as the basis of plastics, adhesives, varnishes or other products.


The opposition to the flow of electric current through a circuit.


An electrical component used to restrict the current in a circuit or part of a circuit. It uses up power and heats up.


In microscopy, the ability to distinguish two separate points or objects as independent. The resolution of a microscope provides a measure of the level of detail it can be used to reveal.


An amplified wave amplitude produced when the frequency of the source matches the natural frequency of the object vibrating.

resource management

Managing human impact on the environment in a way that is sustainable.


Breaking down food (sugar) to get energy.


Measuring the rate of carbon dioxide production or oxygen consumption of an organism or organic system.

resting metabolic rate (RMR)

The energy required to perform vital body functions such as respiration and heart beating while the body is at rest. It accounts for 50–75% of daily energy expenditure.

resultant force

The overall force that acts on an object. For straight-line motion, the resultant force is the sum of the individual forces acting in one direction minus the forces acting in the opposite direction.


A light-sensitive tissue lining the inner surface of the eye. It houses two types of photoreceptor cells – rods and cones.

reverse fault

A fault in which the block of earth on one side of the fault is raised up relative to the surroundings, to create a hanging wall. The Alpine Fault in Westland has a significant component of reverse fault activity.


A pair of tentacle-like structures on the back of the head or neck of some molluscs, including nudibranchs and sea slugs.


A root-like subterranean stem that usually sends roots below and sends up shoots. In ferns, rhizomes can be erect, creeping or vertical (forming a trunk).


A transition metal in Group 9 of the periodic table – symbol Rh, atomic number 45.


A type of rock that contains a lot of silica but not much iron. Includes rocks such as pumice. Often associated with volcanic caldera eruptions.


Cell organelle responsible for making proteins by translating RNA.

Richter scale

A scale of 1–10 indicating the magnitude of an earthquake (the amount of energy it released).


A bone softening and deforming disease, particularly in children, that causes bowed legs, knock-knees, or other deformities of the skeleton.

Ring of Fire

An area around the Pacific Ocean where large numbers of earthquakes and volcanic eruptions occur. It is home to over 75% of the world's active and dormant volcanoes.

riparian strip or zone

The area alongside a river or stream where it meets the land. These regions are natural biofilters, protecting the waterway from pollution and erosion.


Ribonucleic acid. A molecule made up of a large number of nucleotides to form a long single strand. A chemical code for genetic information.

RNA interference

The process when an additional RNA molecule prevents a messenger RNA (mRNA) molecule from being translated into a protein. Also called RNA silencing or RNA inactivation.

rod cells

Photoreceptor cells in the retina of the eye with a cylindrical shape. They can function at lower light intensities than cone cells and play a key role in night vision.


In flight, roll is the movement of the aircraft from side to side about a transverse axis. With an airplane, this means the wings dipping down on one side.

rolling resistance

The force that opposes motion as a tyre (or other rolling object) rolls over the ground. Rolling resistance is caused as energy is converted into heat energy.


Traditional Māori medicine.


An infectious disease, caused by a virus, that is very common in New Zealand and throughout the world. It causes the hospitalisation of about 1000 children in New Zealand every year.

royal jelly

Substance secreted by worker honey bees and fed to all larvae for a short time. Larvae that could become queens get lots of royal jelly for a longer time.

ruminant animals

Cud-chewing, hoofed mammals, for example, sheep, cattle, deer and camels, that have a complex three- or four-chambered stomach. These animals swallow chewed grass into their rumen, a part of their stomach, where billions of microbes eat away at the chewed grass until the animal regurgitates it (the cud) back up and chews it again.

run hours

The cumulative number of hours for which a device or process has been operating.


Water carried away from land to streams and rivers.


A genus of fungi that are native to New Zealand. They form a mutually beneficial relationship with the southern beech trees (Nothofagus spp.).


A transition metal in Group 8 of the periodic table – symbol Ru, atomic number 44.