From Citizendium, the Citizens' Compendium
- Biology : The science of life — of complex, self-organizing, information-processing systems living in the past, present or future.
- Chemistry : The science of matter, or of the electrical or electrostatical interactions of matter.
- Earth science : The study of the components and processes of the planet Earth.
- Atmospheric science : The umbrella term for the study of the Earth's atmosphere.
- Earth's atmosphere : An envelope of gas that surrounds the Earth and extends from the Earth's surface out thousands of kilometres, becoming increasingly thinner (less dense) with distance but always held in place by Earth's gravitational pull.
- Animal : A multicellular organism that feeds on other organisms, and is distinguished from plants, fungi, and unicellular organisms.
- Biogeochemical cycle : Add brief definition or description
- Clean Air Act (U.S.) : A law enacted by the U.S. Congress that defines the responsibilities of the U.S. Environmental Protection Agency (U.S. EPA) for protecting and improving the nation's air quality and the stratospheric ozone layer.
- Combustion : A sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames.
- Electromagnetic radiation : a collection of electromagnetic waves, usually of different wavelengths.
- Electromagnetic spectrum : The range of electromagnetic waves covering all frequencies and wavelengths.
- Flight : The movement of an organism, aircraft or other object in air or other gases.
- Fixed-wing aircraft : Vehicles that remain aloft using the lift from the flow of air over wings which are fixed in position, in relation to the rest of their structure.
- Flight (biology) : Aerial locomotion by living organisms.
- Pitch (dynamics) : Movement of an object, in the vertical plane, with respect to its longitudinal plane, such as diving or climbing
- Roll (dynamics) : A motion of an object in which it rotates along its longitudinal axis, changing its vertical but not horizontal orientation
- Yaw (dynamics) : A change in the orientation of an object, typically a moving object, in the horizontal plane, with the vertical axis held constant
- Human : Bipedal mammalian species native to most continents and sharing a common ape ancestor with chimpanzees, gorillas and orang-utans; notable for evolving language and adapting its habitat to its own needs.
- Life : Living systems, of which biologists seek the commonalities distinguishing them from nonliving systems.
- Light : The part of the electromagnetic spectrum visible to a species' biological eye.
- National Ambient Air Quality Standards : Concentration limits set by the United States Environmental Protection Agency for outdoor ambient air pollutants considered harmful to public health and the environment.
- Natural environment : A term that encompasses all living and non-living things occurring naturally on Earth or some region of Earth.
- Nitrogen : A chemical element, symbolized by N, with an atomic number of 7; the most abundant element in the atmosphere of the Earth.
- Nitrogen cycle : A complex process in which the element nitrogen moves into the air, back down into the soil, is changed chemically by various processes, and returns to the atmosphere once again. This cycle is necessary for life on earth.
- Oxidation : Chemical loss of electrons, gain of oxygen, or loss of hydrogen, from an atom, ion or molecule (oxidation); chemical gain of electrons, loss of oxygen, or gain of hydrogen, from and atom, ion, or molecule (reduction)
- Oxygen : A chemical element with the symbol O and atomic number 8.
- Plant (organism) : A eukaryotic organism, grouped into the kingdom Plantae, that typically synthesizes nutrients through photosynthesis and possesses the inability to voluntarily move.
- Rayleigh scattering : Add brief definition or description