APERIODIC :   

Refers to the lack of symmetry in molecular structures or functions. An important insight into the mechanism of biological structures is their aperiodic composition and distribution of atoms causing the extraordinary complexity of cells.

APHELION   :   

The point in its orbit where a planet is farthest from the Sun.

APOAPSIS   :   

The point in orbit farthest from the planet.

APOGEE   :   

The point in orbit farthest from the Earth.

APPLET   :   

The small program that is written in Java programming language and was designed to provide interactivity on web pages.

APPLICATION   :   

A program that is designed to perform specific tasks is known as an application. Internet explorer, Adobe Photoshop are some popular applications.

APPLICATION SERVER   :   

The sole responsibility of running specific applications within the network lies with a specialized server that is based in a client/server network is known as application server.

AQUIFERS   :   

Underground formations, usually composed of sand, gravel, or permeable rock, capable of storing and yielding significant quantities of water.

ARAGONITE   :   

A carbonate mineral that forms naturally in almost all mollusk shells, as well as the calcareous endoskeleton of warm- and cold-water corals

ARCHAEA   :   

A major division of microorganisms belonging to kingdom Monera in the traditional five-kingdom taxonomy. Like bacteria, Archaea are single-celled organisms lacking nuclei and are therefore prokaryotes.

ARGUMENT OF PERIHELION   :   

The measurement of an angle along the orbit of a planet or other solar system object from the ascending node is known as argument of perihelion. It corresponds to right ascension and longitude.

ARITHMETIC LOGIC UNIT (ALU)   :   

This is the mathematical core circulatory that mathematically and logically calculates the results of binary data and is applied to all the central processing units (CPU) in computers.

ARTESIAN   :   

Describes a confined aquifer containing groundwater that will flow upwards out of a well without the need for pumping.

ASH   :   

The fine-grained material produced by a pyroclastic eruption. An ash particle is defined to have a diameter of less than 2 millimeters.

ASTEROID NUMBER   :   

Asteroids are assigned a serial number when they are discovered; it has no particular meaning except that asteroid N+1 was discovered after asteroid N.

ASTHENOSPHERE   :   

Ductile rocks that lie from below the lithosphere to 250 km below the surface.

ATMOSPHERE   :   

The blanket of air that surrounds the Earth. It is thickest near the ground and gradually fades away to nothing in outerspace.

ATMOSPHERIC LAPSE RATE   :   

The constant decline in temperature of an air parcel as it rises in the atmosphere due to pressure drop and gas expansion. It is an adiabatic charge.

ATOM   :   

The smallest unit of matter as recognized by chemical properties of molecules. Atoms are composed of protons, neutrons and electrons. The latter provide all properties described by molecular interactions and chemical reactions that are essential processes in biology.

ATOMS   :   

Atoms made up of protons and neutrons in a central nucleus surrounded by electrons. The smallest particle of a chemical element that can take part in a chemical reaction without being permanently changed.

ATP   :   

Short for Adenosine triphosphate, a nucleotide and universal energy currency for metabolism. Almost all caloric content of food is converted into ATP before it can be utilized for tissue growth, muscle work and other physiological processes.

AURORA   :   

A glow in a planet's ionosphere caused by the interaction between the planet's magnetic field and charged particles from the Sun.

AURORA BOREALIS   :   

The Northern Lights caused by the interaction between the solar wind, the Earth's magnetic field and the upper atmosphere; a similar effect happens in the southern hemisphere where it is known as the aurora australis.