aphelion -  Regarding our earth's quasi-elliptical orbit, the point Earth is farthest
 from Sol.  It occurs near 5 July, with our Earth's center 151766000 km from the mean location 
 of Sol. The point on an ellipse farthest from its center is called apogee, and "Helios" is
 a Greek word for "Sun".

astronomical unit (AU) -  Radius of circular about Sol of a particle at the limit
 of no mass, which would have an orbital period of 2 PI/k days, with k being the Gaussian
 gravitational constant of .01720209895.  It is 149457000 km.  As a consequence, mean
 distance from our earth's center to the mean location of our sun is 1.000001018 AU.

circumsolar -  Typically bright region surrounding our sun, as seen thru our
 atmosphere. It includes the atmospheric solar corona.

electromagnetic radiation -  Energy emission, effects of which can be described as
 orthogonal alternating electric and magnetic "waves".  Observation of such emission as
 existing in discrete quanta means it can also be described as consisting of energetic
 photons.  Very nearly all energy emitted by our sun is of this form.

electromagnetic spectrum -  Distribution according to frequency (or wavelength) of
 electromagnetic radiation.

energy -  Mass x distance2 / time2.  It is a measure of ability of an object or
 continuum to modify its environment (move objects or its surrounding continuum).

flux -  Quantity of matter or magnitude of a property(ies) per area per time.
 E.g., if solar photons with total energy 5000 J are incident to a collector of area 2
 m2 during 10 sec, then solar energy flux is 250 W/m2 (J/sec/m2).

optical air mass -  Mass of atmosphere solar energy must pass directly thru to reach
 our earth's surface, relative to standard mass of our atmosphere at seal level.

perihelion -  Regarding our earth's quasi- elliptical orbit, the point our earth is
 closest to Sol.  It occurs near 3 January, with our earth's center 146771000 km from the
 mean location of Sol.  The point on an ellipse closest to its center is called perigee,
 and "Helios" is a Greek word for "Sun".

solar constant -  Mean solar energy flux perpendicular with the solar beam in outer
 space, at mean distance from our earth's center to our sun.  It is approximately 1370 w/m2.

solar energy - Energy emitted from Sol in the form of electromagnetic radiation.
 
solar energy, backscattered -  Solar energy scattered down to our earth's surface
 which had previously been ground-reflected.

solar energy, cloud-reflected -  Solar energy reflected from atmospheric clouds
 (including that ground-reflected previously).

solar energy, cloud-transmitted -  Solar energy scattered downward thru atmospheric
 clouds.

solar energy, diffuse -  Solar energy scattered by our atmosphere and/or ground.
 With no further specification, the term "diffuse solar energy flux" means that incident
 to horizontal.

solar energy, direct -  Solar energy transmitted thru our atmosphere without being
 scattered.  With no further specification, the term "direct solar energy flux" means that
 incident to the horizontal.

solar energy, extraterrestrial -  Solar energy in outer space.  With no further
 specification, the term "extraterrestrial solar energy flux" means that which would
 be incident to a location in absence of our atmosphere.  It is so called, being a very
 close approximation for solar energy flux at outer reaches of our atmosphere.

solar energy, global -  Solar energy flux from all directions.  Thus, it is the sum
 of direct and diffuse solar energy.  With no further specification, the term "global solar
 energy flux" means that incident to the horizontal.

solar energy, ground-reflected -  Solar energy reflected from ground or objects near
 ground.

solar energy, sky diffuse -  Solar energy scattered downward thru cloudless sky areas.

solar energy components -  Solar energy distribution in our atmosphere, specified by
 causes of its scattering and absorption.