A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
Aplanatic Points
See Aplanatism
Aplanatism
The property of
the surface by virtue of which all rays starting from a particular point object
on its axis, after reflection or refraction at the surface, converge or appear
to diverge from a single point image, is called aplanatism and the particular
object and image points are called aplanatic points while the surface is said
to be aplanatic surface with respect to those two points.
Apochromat
A term applied to
photographic & microscope objectives indicating highest degree of color
correction.
Apogee
Point at which a
satellite or any object orbiting earth is farthest from center of earth. At its
apogee, object travels slower than at any other point in orbit.
Arc
The
arc refers to the set of points on a circle that lie in the interior of circle.
The arc can be any part of circumference.
or
The
arc is a closed segment of a differentiable curve in the 2D plane.
Archimedes Principle
As per this
principle when a body is fully or partially submerged in a fluid, a buoyant
force from the surrounding fluid acts on the body. The force is directed upward
and has a magnitude equal to weight on fluid that has been displaced by body.
Area
It is
mathematical quantity that describes the amount of space extended by two
dimensional surface area in the plane.
Artificial
Transmutation
An artificially
induced nuclear reaction caused by the bombardment of a nucleus with subatomic
particles or small nuclei. The phenomenon was first observed and proposed by
Ernest Rutherford.
Asteroids
They are small,
rocky objects revolving around the sun that are too small to be called planets.
They are also called Planetoids.
Astigmatism
Defect in optical
system where rays that propagate in two perpendicular planes have different
foci. It is a vision condition that causes blurred vision either due to the
irregular shape of cornea, the clear front cover of the eye, or sometimes the
curvature of the lens inside the eye. An irregular shaped cornea or lens
prevents light from focusing properly on the retina, the light sensitive
surface at the back of the eye. As a result, vision becomes blurred at any distance.
Astronaut
A person who is
trained to pilot, navigate, or otherwise participate as a crew member of a
space craft is known as Astronaut.
Astronomical
Unit (au)
An
astronomical unit is approximately mean distance between Earth and Sun. It is a
derived constant and used to indicate distances with in solar system. Symbol au
is recommended by international astronomical union.
1a.u. = 149,597,870.691 KM
Astronomy
It is the Branch
of science which deals with study of universe comprising celestial objects such
as planets, stars etc. outside earth atmosphere. The study covers evolution,
composition, motion, etc of universe.
Astrophysics
The branch of
astronomy that deals with the physical and chemical processes that occur in
stars, galaxies and interstellar space is called Astrophysics. Astrophysics
deals with structure & evolution of stars, properties of interstellar space
and its interaction with system of stars, and with structure and dynamics of
cluster of stars such as galaxies.
Athermanous
Substances opaque
to the thermal radiation are called athermanous.
Atmosphere
The mixture of
gases surrounding the earth or other celestial body, held in place by gravity
is referred to as atmosphere. It forms five distinct layers at different
heights. The earth’s atmosphere consists in ascending order, the Troposphere
(containing 90% of the atmosphere mass), the Stratosphere, the Mesosphere, the Thermosphere
and Exosphere. Atmosphere is composed primarily of Nitrogen (78%), Oxygen (21%)
and plays major role in water cycle, Nitrogen cycle & Carbon cycle.
Atmospheric
Electricity
The conductivity
of atmosphere arises from ions created by cosmic rays. The conductivity is
variable; as we go to higher altitudes, conductivity gradually increases and at
about 50km, atmosphere is pretty good conductor. This electrical phenomenon
takes place between two conducting spherical surfaces, earth and top of
stratosphere. Each of these surfaces is equipotential.
Atmospheric
Pressure
The atmospheric
air exerts normal pressure upon all surfaces with which it is in contact, and
is known as atmospheric pressure.
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