RADIAN   :   

It is SI unit of plane angle. The radian is defined as the angle subtended at the centre of a circle by an arc of the circumference equal in length to the radius of the circle. There are 2p radians in a circle.

RADIATION   :   

The heat transfer between two bodies without change in the temperature of the intervening medium is known as radiation. Radiation is also the release of energy from a source.

RADIATION BELT   :   

Regions of charged particles in a magnetosphere.

RADICAL   :   

Atomic or molecular species with unpaired electrons on an otherwise open shell configuration. These unpaired electrons are usually highly reactive, so radicals are likely to take part in chemical reactions.

RADIO CARBON DATING   :   

A radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of carbonaceous materials up to about 60,000 years.

RADIO METRIC DATING   :   

A technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. It is the principal source of information about the age of the Earth and a significant source of information about rates of evolutionary change.

RADIO WAVES   :   

The waves which have a frequency range of few kilo hertz to few hundred mega hertz are known as radio waves.

RADIOACTIVITY   :   

The spontaneous decay of atomic nuclei is known as radioactivity. During radioactivity, aloha particles, beta-rays and gamma rays are emitted.

REACTION   :   

When two or more chemicals combine to make a new chemical substance.

REALIZED NICHE   :   

The ecological role that an organism plays when constrained by the presence of other competing species in its environment

RECHARGE   :   

A hydrologic process where water moves downward from surface water to groundwater. This process usually occurs in the vadose zone below plant roots, and is often expressed as a flux to the water table surface.

RECOMBINANT DNA   :   

The DNA that us created by combination of DNA sequences that do not occur naturally is known as reconbinat DNA.

RED GIANT   :   

An old star that has low surface temperature and a diameter that is large relative to the Sun.

REFERENCE DOSE   :   

The U. S. Environmental Protection Agency's maximum acceptable oral dose (abbreviated RfD) of a toxic substance, most commonly determined for pesticides.

REFRACTION   :   

The bending of a wave path, as of light or sound, at the boundary between two different mediums.

REGIO   :   

Region.

REGOLITH   :   

The layer of rocky debris and dust made by metoritic impact that forms the uppermost surface of planets, satellites and asteroids.

RELATIVE HUMIDITY   :   

The ratio of the amount of water vapor present in a specified volume of air to the maximal amount that can be held by the same volume of air at a specified temperature and pressure.

RELATIVITY   :   

The relative values of time, motion, mass and energy of a body in motion is known as relativity.

RENEWABLE RESOURCES   :   

Supplies of biological organisms that can be replaced after harvesting by regrowth or reproduction of the removed species, such as seafood or timber.

REPLACEMENT LEVEL   :   

The number of children per woman necessary to keep population levels constant when births and deaths are considered together over time; estimated to be an average of 2.1 children for every woman.

RESIDENCE TIME   :   

A broadly useful concept that expresses how fast something moves through a system in equilibrium; the average time a substance spends within a specified region of space, such as a reservoir. For example, the residence time of water stored in deep groundwater, as part of the water cycle, is about 10.000 years.

RESOLUTION   :   

The amount of small detail visible in an image; low resolution shows only large features, high resolution shows many small details.

RESONANCE   :   

When a body vibrates under the influence of another body having frequency equal to its own frequency its amplitude of vibrations increases to an optimum value. Such oscillations are called resonant oscillations and the phenomenon as resonance.

RESPIRATION   :   

Metabolism of an individual cell, tissue, or organism that results in the release of chemical energy derived from organic nutrients.

RETINA   :   

The retina is a light-sensitive layer located at the back of the eye that covers about 65 percent of its interior surface. It may be described as the "screen" on which an image is formed by light that has passed into the eye via the cornea, aqueous humour, pupil, lens, then the hyaloid and finally the vitreous humour before reaching the retina. The function of the retina is not just to be the screen onto which an image may be formed, but also to collect the information contained in that image and transmit it to the brain in a suitable form for use by the body. It contains photosensitive cells (called rods and cones) in the retina and their associated nerve fibres that convert incident light energy into signals that are then sent onto the brain along the optic nerve.

RETROGRADE   :   

The rotation or orbital motion of an object in a clockwise direction when viewed from the north pole of the ecliptic; moving in the opposite sense from the great majority of solar system bodies.

REVOLUTION   :   

The rotation of a planet around the Sun through 360 degrees or a full circle is known as revolution.

RHESUS FACTOR   :   

The 5 antigens, namely C, c, D, E and e that are found on the surface of red blood cells is known as Rhesus factor. The antigen that is commonly referred as Rhesus factor is Rh D antigen only. It is named after the Rhesus Macaque, after discovery of the factor by Karl Landsteiner and Alexander Wiener using red blood cells from rhesus monkey.

RHYOLITE   :   

Fine-grained extrusive igneous rock, commonly with phenocrysts of quartz and feldspar in a glassy groundmass.

RIBONUCLEIC ACID (RNA)   :   

The biological molecule that contains long chains of nucleotide units of a nitrogenous base, a ribose sugar and a phosphate is known as Ribonucleic acid. RNA is single stranded molecule with ribose, unlike DNA that is double stranded with deoxyribose. Another difference between a DNA and RNA molecule is presence of base uracil instead of thymine in RNA.

RIFT   :   

A fracture or crack in a planet's surface caused by extension. On some volcanoes, subsurface intrusions are concentrated in certain directions; this causes tension at the surface and also means that there will be more eruptions in these "rift zones."

RIFT VALLEY   :   

An elongated valley formed by the depression of a block of the planet's crust between two faults or groups of faults of approximately parallel strike.

RIMA   :   

A fissure.

RISK ANALYSIS   :   

Identifying potential issues and risks ahead of time before these were to pose cost and/ or schedule negative impacts.

RISK ASSESSMENT   :   

An analytical study of the probabilities and magnitude of harm to human health or the environment associated with a physical or chemical agent, activity, or occurrence.

RISK MANAGEMENT   :   

The human activity that integrates recognition of risk, risk assessment, development of strategies to manage it, and mitigation of risk using managerial resources.

ROTATION   :   

The act of a mass of body moving in a circle around its axis or fixed point is known as rotation.

R-SELECTED   :   

Species with a reproductive strategy to produce many offspring, each of whom is, comparatively, less likely to survive to adulthood.

RUMINANT   :   

Any hooved animal that digests its food in two steps, first by eating the raw material and regurgitating a semi-digested form known as cud, then eating (chewing) the cud, a process called ruminating.

RUPES   :   

The term applied to scarps on planetary surfaces; many scarps are thought to be the surface expression of faults within the crust of the planetary object.