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SOLAR
SYSTEM
STARS
BLACK
HOLES
METEORS
AND METEORITES
ASTEROIDS
COMETS
GALAXIES
NEBULAE
GLOSSARY
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Glossary
of Terms
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Click on the
links to view the Glossary :
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A
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ASTEROIDS:Small
bodies composed of rock and metal which orbit the Sun.
Most [95%] lay in a belt between the orbits of the planets
Mars and Jupiter, also known as a minor planet.
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ASTRONOMICAL UNIT:A
unit of distance which is approximately (within about
3/100,000,000) the average Distance from the
Earth to the Sun, this distance is approximately 149597870
km. Abbreviated AU.
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AURORA:A
glow in a planet's ionosphere caused by the interaction
between the planet's magnetic field and charged particles
from the Sun [solar wind].
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ABSOLUTE ZERO:The
lowest possible temperature, at which a substance contains
no heat energy.
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| ACCELERATION:The
rate at which the speed of an object is changing. |
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ANTHROPIC PRINCIPLE:We
see the universe the way it is because if it were different,
we would not be here to observe it.
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ANTIPARTICLE:Each
type of matter particle has a corresponding antiparticle.
When a particle collides with its antiparticle, they
annihilate, leaving only energy.
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ATOM:The
basic unit of ordinary matter, made up of a tiny nucleus(consisting
of protons and neutrons) surrounded by orbiting electrons.
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| B |
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BIG BANG:The singularity at the
beginning of the Universe.
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BIG CRUNCH:The singularity at
the end of the Universe.
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BLACK HOLE:A region of space-time
from which nothing, not even light, can escape because
gravity is so strong.
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| C |
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CELESTIAL EQUATOR:The intersection
of the equatorial plane of the Earth with the celestial
sphere, the projection of the Earth's equator onto the
sky.
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| CONJUNCTION:The alignment
of two celestial objects such that the difference in their
longitude, as seen from Earth, is 0 degree. Two objects
may also be in conjunction in right ascension. When one
of the objects is the Sun 'conjunction' denotes when the
other object is in line with the Sun and therefore is
usually invisible. |
| CONSTELLATION:One of
88 arbitrary configurations of stars, the area of the
celestial sphere containing one of these configurations. |
| CRATERS:Roughly, circular
depression on the surface of many objects in the Solar
System, most craters were created through meteoritic impact,
with the reminder being volcanic or caused by surface
collapse. |
| CRESCENT:A phase of
the moon or other celestial body where the percentage
of visible surface illumination is greater than 0% but
less than 25 %( or 50% of the side currently being observed). |
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CHANDRASEKHAR LIMIT:The maximum
possible mass of a stable cold star, above which it
must collapse to a black hole.
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CONSERVATION OF ENERGY:The law
of science that states that energy(or its equivalent
in mass) can neither Be created not destroyed.
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COORDINATES:Numbers that specify
the position of a point in space and time .
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COSMOLOGICAL CONSTANT:A mathematical
device used by Einstein to give space-time an inbuilt
tendency to expand.
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COSMOLOGY:The study of Universe
as a whole.
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| D |
| DAY:Generally defined as one rotation
of a planet on its axis. A sidereal day is measured with
respect to the stars, while a Solar Day is measured with
respect to the Sun. Many other types of days are defined. |
| DEGREE (OF ARC):1/360
of a Circle, 1degree of arc contains 60 mins of arc, designated
degree; thus 85 degree 18 mins 08 second. |
| DIAMETER:The length from the surface
of a celestial object, through its center, to the surface
on the other side, the diameter is twice the radius. |
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| E |
| ECCENTRICITY:A measurement
from (0 to 1) which is the amount that the orbit of any
Solar System objects is not circular. An object in a circular
orbit would have an eccentricity of 0. Mathematically,
this is defined as the distance between the focal points
of an ellipse divided by twice the length of the major
axis. |
| EPHEMERIS TIME:The
time scale that together with the laws of motion correctly
predicts the positions to celestial bodies, and it is
therefore used as the argument in the ephemerides. The
current ephemeris time (ET) is thus determined by comparing
the observed positions with the ephemerides. |
| EQUINOX:Either of two
points on the ecliptic, lying at right ascension 0 hours
(March Equinox) and 12 hours (September Equinox). |
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ELECTRIC CHARGE:A property of
the particle by which it may repel(or attract) other
particles that have a charge of similar (or opposite)
sign.
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ELECTROMAGNETIC FORCE:The force
that arises between particles with electric charge,
the second strongest of the four fundamental forces.
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ELECTRON:A particle with a negative
electric charge that orbits the nucleus of an atom.
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ELECTROWEAK UNIFICATION ENERGY:The
energy (around 100 GeV) above which the distinction
between the electromagnetic force and the weak force
disappears.
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ELEMENTARY PARTICLE:A particle
that, it is believed, cannot be divided.
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EVENT:A point in space-time, specified
by its time and place.
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EVENT HORIZON:The boundary of
a black hole.
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EXCLUSION PRINCIPLE:Two identical
spin-1/2 particles cannot have(within the limits set
by the Uncertainty Principle) both the same position
and the same velocity.
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| F |
| FOURTH CONTACT:During
an eclipse, the moment that the shadow of the eclipsing
body breaks contact with the body being eclipsed, the
end of eclipse. |
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FIELD:Something that exists through
out space and time, as opposed to a particle that exists
at only one point at a time.
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FREQUENCY:For a wave, the number
of complete cycles per second.
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| G |
| GREENHOUSE EFFECT:The
heating of a planetary atmosphere through the following
process visible radiation fro m the Sun passes through
the atmosphere and is absorbed by the surface. It is later
re-radiated as infrared radiation, which is absorbed and
re-emitted by the atmosphere. |
| GREGORIAN CALENDAR:The
calendar in general use today, introduced in 1582 by Pope
Gregory XIII as a revision of the Julian calendar, adopted
in Britain and the American Colonies in 1752, and having
leap years in every year divisible by 4 with the restriction
that centennial year are leap years only when divisible
by 400, for e.g. the 1700, 1800 and 1900 are not leap
years, but 2000 is a leap year. |
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GAMMA RAY:Electromagnetic waves
of very short wavelength, produced in radioactive decay
or by collisions of elementary particles.
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GENERAL RELATIVITY:Einstein's
Theory based on the idea that the laws of science should
be same for all observers, no matter how they are moving.It
explains the force of gravity in terms of the curvature
of a four-dimensional space-time.
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GEODESIC:The shortest (or longest
) path between two points.
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GRAND UNIFICATION THEORY:The energy
above which, it is believed, the electromagnetic force,
wear force and strong force become indistinguishable
from each other.
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GRAND UNIFIED THEORY:A theory
that unifies the electromagnetic, weak and strong forces.
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| I |
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ION:An ion is an atom or molecule
that has either lost one or more of its electrons and
thus has a positive electric charge or gained one or
more electrons in the later case the ion will have a
negative charge.
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| IONOSPHERE:A region
of charged particles in a planet's upper atmosphere, the
part of the Earth's atmosphere beginning at the altitude
of approximately 400 km and extending outward 400 km or
more. |
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IMAGINARY TIME:Time measured using
imaginary numbers.
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| K |
| KEELER DIVISION:A division
35 km in width, lying in the outer A-ring of the Saturnian
Ring System. |
| KELVIN:A unit of temperature
from the absolute temperature scale. At absolute 0- 0
K molecules of all substances have no heat energy. The
temperature in K is that in Degree C + 273.15 |
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| L |
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LIGHT CONE:A surface in space
time that makes out the possible for light rays passing
through a given event.
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LIGHT SECOND:Distance traveled
by light in one second.
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LIGHT YEAR:Distance traveled by
light in one year.
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| M |
| MAGNITUDE:Within the
confines of the Solar System this usually refers to the
apparent visual magnitude, which is the brightness of
a celestial object as seen from Earth irrespective of
its true brightness. |
| MENSA:A Mensa, flat
topped elevation with cliff-like edges on the surface
of a planet or a satellite. |
| METONIC CYCLE:A lunar
cycle (discovered by the Greek astronomer Meton in the
15th century B.C.)=19 years after which the phases of
the Moon will recur on the same days of the year. |
| MERIDIAN:The great circle passing
through the observer's zenith and the celestial poles. |
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MAGNETIC FIELD:The field responsible
for magnetic forces, now incorporated, along with the
electric field, into the electromagnetic field.
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| MASS:The quantity of matter in
a body, its inertia, or resistance to acceleration. |
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MICROWAVE BACKGROUND RADIATION:The
radiation from the glowing of hot early universe, now
so greatly red-shifted that if appears not as light,
but as microwaves(radio-waves with a wavelength of a
few centimeters).
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| N |
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NEUTRINO:An extremely light(possibly
massless) elementary matter particle that is affected
only by the weak force and gravity.
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NEUTRON:An uncharged particle,
very similar to the proton, which accounts for roughly
half the particles in the nucleus of most atoms.
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NEUTRON STAR:A cold star, supported
by the exclusion principle repulsion between neutrons.
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NO BOUNDARY CONDITION:The idea
that the Universe is finite but has no boundary(in imaginary
time).
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NUCLEAR FUSION:The process in
which two nuclei collide to coalesce to form a single,
heavier nucleus.
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NUCLEUS:The central part of an
atom consisting of only protons and neutrons, held together
by the strong force.
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| O |
| OZONE LAYER:A layer
of ozone that lies between 12 and 50 km above the Earth's
surface. Formed by the action of the Solar UV radiation
on atmospheric oxygen, it is of vital importance to the
Earth because it absorbs damaging UV radiation from the
sun. |
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| P |
| PARALLAX:The apparent angular displacement
of a star or other celestial object that results from
the revolution of the Earth about the Sun, for a star,
numerically, this is the angle subtended by one AU at
the distance of the particular object. This differs from
the Solar Parallax, which is the apparent displacement
of the Sun as seen form two places of Earth. |
| PERIHELION:The position of an object
in Solar Orbit when it is closest to the Sun, the instant
in a given orbit of a planet, (or other body) when it
is closest to the Sun. |
| POLES:Two points of a planet, satellite
or other celestial object which lie 90 degree above or
below a given great circle, generally the object's Equator. |
| PROTON:A hadron resides in the
nucleus of an atom and possessing one positive electric
charge. It is composed of three quarks and its mass is
about 1836 times that of an electron.The positively charged
particles that make up roughly half the particles in the
nucleus of most atoms. |
| POLARIZATION:Waves of radiation
lie at right angles to the direction in which they are
moving. They are at all angles perpendicular to this direction
unless the radiation is linearly polarized, when the waves
lie in one plane. However, these planes can rotate, the
wave is then said to be circularly polarized. |
| PARSEC:The distance at which a
body would have an annual parallax of one second of arc.
It equals 3, 26 light years. No star is near to the Sun
as this. |
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PARTICLE ACCELERATOR:A machine
that, using electromagnets,can accelerate moving charged
particles, giving them more energy.
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PHASE:For a wave, the position
in its cycle at a specified time: a measure of whether
it is at a crest, a trough or at some point in between.
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PHOTON:A quantum of light.
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PLANCK'S QUANTUM PRINCIPLE:The
idea that light(or any other classical waves) can be
emitted or absorbed only in discrete quanta, whose energy
is proportional to their frequency.
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POSITRON:The (positively charged)
antiparticle of the electron.
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PRIMORDIAL BLACK HOLE:A black
hole created in the very early Universe.
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| Q |
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QUANTUM:The indivisible unit in
which waves may be emitted or absorbed.
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QUANTUM MECHANICS:The theory developed
from Planck's quantum principle and Heisenberg's uncertainty
principle.
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QUARK:A (charged) elementary particle
that feels the strong force.Protons and neutrons are
each composed of three quarks.
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| R |
| ROCHE LIMIT:The minimum distance
from the center of a planet that a satellite can maintain
equilibrium, that is, without being pulled apart by tidal
forces. If a planet and a Moon have the same density;
the Roche limit is 2446 times the radius of the planet. |
| RADIUS:The length from
the center of a celestial object to its surface, the radius
is half the diameter. |
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RADAR:A system using pulsed radio
waves to detect the position of objects by measuring
the time a single pulse takes to reach the object and
be reflected back.
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RADIOACTIVITY:The spontaneous
break-down of one type of atomic nucleus into another.
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RED-SHIFT:The reddening of light
from a star that is moving away from us, due to Doppler's
effect.
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| RED DWARF:A dim red star at the
lower end of the main sequence [q.v.] with surface temperature
of 2500-5000K. |
| RADIO TELESCOPE:A telescope
for receiving and imaging celestial radio sources. Its
form can range from arrays of antennae arranged to observe
inerferometrically as in aperture synthesis telescopes
and very large arrays, to a dish type of telescope, analogous
to the optical reflector. Such dishes can be linked to
make a large inferometer. |
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| S |
| SOLSTICE:Either of
two points on the Ecliptic lying at right ascension 6
hours (June Solstice) and 18 hours (December Solstice). |
| SPECTRUM:The Spectrum formed by
a celestial object where wavelengths are manifested by
patterns of dark lines or bands signifying a decrease
in intensity of radiation at those wavelengths, such decreases
allow the percentage of each of the absorbing substance
s to be measured, thus determining the composition of
the object. |
| STRATOSPHERE:The cold
region of a planetary atmosphere above the convecting
regions, usually without vertical motion of the gases
but some times exhibiting strong horizontal jet streams. |
| SYZYGY:The lineup of
the Sun, the Earth and either the Moon or a planet. For
the moon, this occurs at new Moon and full Moon. For a
planet, it occurs at conjunction and opposition. |
| SPACE TIME:A combination
of three dimensions of space and one of time, allowing
events to be described mathematically using four coordinates.Four
dimensional space whose points are events. |
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SINGULARITY:A point in space-time
at which the space-time curvature becomes infinite.
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SINGULARITY THEOREM:A theorem
that shows that a singularity must exist under certain
circumstances - in particular, that the Universe must
have started with a singularity.
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SPATIAL DIMENSION:Any of the three
dimensions of space-time that are space-like i.e. any
except for the time dimension.
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SPECIAL RELATIVITY:Einstein's
theory based on the idea that laws of science should
be same for all freely moving observers, no matter what
their speed.
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SPECTRUM:The splitting of, say,
an electromagnetic wave into two component frequencies.
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SPIN:An internal property of elementary
particles, related to but not identical to, the everyday
concept of spin.
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STATIONARY STATE:One that is not
changing with time: a sphere spinning at constant rate
is stationary because it looks identical at any instant,
even though it is not static.
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STRONG FORCE:The strongest of
all the four fundamental forces, with the shortest range
of all. It holds the quarks together within the protons
and neutrons, and holds the protons and neutrons together
to from atoms.
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| U |
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UNCERTAINITY PRINCIPLE:One can
never be exactly sure of both the position and the velocity
of a particle; the more accurately one knows the one,
the less accurately one know the other.
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| V |
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VIRTUAL PARTICLE:In quantum mechanics,
a particle that can never be directly dictated but whose
existence does have measurable effects.
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| W |
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WAVELENGTH:For
a wave, the distance between two adjacent troughs or
two adjacent crests.
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WAVE PARTICLE DUALITY:The
concept in quantum mechanics that there is no distinction
between waves and particles; particles may sometimes
behave like waves, and waves like particles.
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WEAK FORCE:The
second weakest of the four fundamental forces with a
very short range.It effects all mater particles but
not force-carrying particles.
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WEIGHT:The
force exert on a body by a gravitational field.It is
proportional to, but not the same as, its mass.
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WHITE DWARF:A
stable cold star, supported by the exclusion principle,
repulsion between electrons.
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