R

radar
Radio detection and ranging device that emits radio waves and receives them after they bounce on the nearest surface. This creates an image of storms and other nearby objects.
radiation
The movement of energy through empty space between objects by electromagnetic waves.
radiative zone
Layer of the Sun immediately surrounding the core where energy moves atom to atom as electromagnetic waves.
radio telescope
A radio antenna that collects radio waves or microwaves.
radio wave
The longest wavelengths of the electromagnetic spectrum; 1 mm to more than thousands of kilometers.
radioactive isotope
Substance that is unstable and likely to decay into another isotope.
radioactivity
Emission of high-energy particles by unstable isotopes.
radiometric dating
Process of using the concentrations of radioactive substances and daughter products to estimate the age of a material.
radiosonde
A group of instruments that measure the characteristics of the atmosphere — temperature, pressure, humidity, etc. — as they move through the air.
rainforest
The tropical wet biome where temperatures are warm and rain falls nearly every day.
rainshadow effect
A location of little rain on the leeward side of a mountain range due to descending air.
reclamation
Restoring a mined property to its pre-mining state.
red giant
Stage in a star’s development when the inner helium core contracts while the outer layers of hydrogen expand.
redshift
Shift of wavelengths of light towards the red end of the spectrum; happens as a light source moves away from us.
reef
A large underwater structure created from the calcium carbonate skeletons of coral.
reflecting telescope
Telescopes that use mirrors to collect and focus light.
reflection
Bouncing back. A wave bounces off a reflective surface, just as a light wave bounces off a mirror.
refracting telescope
Telescopes that use convex lenses to collect and focus light.
refraction
A change in the direction of a wave caused by a change in speed. Waves refract when they travel from one type of medium to another.
regional metamorphism
Changes in rock that occur because of high pressure over a large area.
relative age
The age of an object in comparison with the age of other objects.
relative humidity
The amount of water vapor in the air relative to the maximum amount of water vapor that the air could contain at that temperature.
relief
Difference in height of landforms in a region.
renewable resources
Resources that are limitless or that are replaced more quickly than we can use them.
reservoir
A storage location for a substance, such as water. The atmosphere is a reservoir for carbon dioxide.
residence time
The amount of time, on average, a substance remains in a reservoir.
residual soil
Soil that forms from the bedrock upon which it lies.
respiration
The process in which organisms convert sugar into useful food energy. Respiration burns oxygen and produces carbon dioxide.
reverse fault
A dip-slip fault in which the hanging wall pushes up relative to the footwall.
revolution
The Earth’s movement around the Sun in an orbital path.
rip current
A strong surface current that returns to the ocean from the shore.
RNA world hypothesis
RNA was the first nucleic acid and the only one at the beginning of life.
rock
Mixture of minerals.
rock cycle
The never-ending cycle in which one rock type changes into another rock type.
rocket
A device propelled by particles flying out one end at high speed.
rotation
The motion of the Earth spinning on its axis.