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 |
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AE index |
A geomagnetic index describing
the auroral electrojet. |
Aether(Quinta essentia) Latin |
The clear sky or the upper air. |
ap index |
A
mean, 3-hourly "equivalent amplitude" of
magnetic activity based on K index data from a
planetary of 11 Northern and 2 Southern Hemisphere
magnetic observatories between the geomagnetic
latitudes of 46 and 63 degrees. ap values are given
in units of 2 nT. |
Ap
index |
A
daily index determined from eight ap index values. |
Aphelion |
The
point in the orbit of a planet, comet, etc. which
is furthest from the sun. |
Astrophysics |
The
branch of astronomy and physics that deals with
the physics of astronomical objects. |
Atmosphere |
The layer of gas
surrounding the earth or other planets. The upper atmosphere
is the region of the Earth's atmosphere above the
troposphere (which extends to about 20 km). Regions
of the upper atmosphere are the stratosphere, mesosphere
and thermosphere. |
Aurora (or
Southern/Northern Lights) |
A sporadic, faint
visual phenomena associated with geomagnetic activity
that occurs mainly in the high-latitude night sky.
Auroras occur within a band of latitudes known as
the auroral oval, the location of which is dependent
on geomagnetic activity. Auroras are a result of
collisions between atmospheric gases and precipitating
charged particles (mostly electrons) guided by the
geomagnetic field from the magnetotail. Each gas
(oxygen and nitrogen molecules and atoms) gives out
its own particular color when bombarded, and atmospheric
composition varies with altitude. The auroral altitude
range is 80 to 1000 km, but typical auroras are 100
to 250 km above the ground; the color of the typical
aurora is yellow-green, from a specific transitions
of atomic oxygen. Auroral light from lower levels
in the atmosphere is dominated by blue and red bands
from spectral line of atomic oxygen. The patterns
and forms of the aurora include quiescent arcs, rapidly
moving rays and curtains, patches, and veils. |
Auroral
electrojet |
A current that flows
in the ionosphere in the auroral zone. |
Auroral Oval |
The pattern of auroral
light around the north and south poles. The auroral
oval expands and contracts over a period of hours
and days, depending on geomagnetic activity. |
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|
Bartel'
rotation number |
The serial number
assigned to 27-day rotation periods of solar and
geophysical parameters. Rotation 1 in this sequence
was assigned arbitrarily by Bartels to begin in January
1833, and the count has continued by 27-day intervals
to present. (For example, rotation 2195 began on
April 17, 1994). The 27-day period was selected empirically
from the observed recurrence of geomagnetic activity
attributed to corotating features on the sun. |
Bow shock |
A collisional shock
wave in front of the magnetosphere arising from the
interaction of the supersonic solar wind with earth's
magnetic field. |
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|
Chromosphere |
Layer of glowing
gas surrounding Sun or a star. |
Comet |
A small body of
ice and dust which orbits the Sun. |
Conservation
of Momentum |
A fundamental law
of motion, equivalent to Newton's laws: in a system
of bodies (=objects), the (vector) sum of all momenta
cannot change due to any internal interactions. |
Corona |
The very hot outer
layer of the Sun's atmosphere, composed of highly
diffused, superheated, iodized gases, and extending
into interplanetary space. The hot gases in the solar
corona from the solar wind. |
Coronal
Mass Ejection(CME) |
A vast region of
hot, dense, and high speed solar wind propagating
away from the Sun. |
Cosmic
Rays |
Nuclear and subatomic
particles moving through space at speeds close to
the speed of light. They are thought to come from
stars in the Milky Way galaxy. |
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|
Dynamics
Explorer
(or DE) |
The name of a two-spacecraft
mission launched in 1981 and operated until 1989
to study the auroral regions and their interaction
with the Earth's magnetosphere. |
DSAD |
Digital
Solar Attitude Sensor (used for sun sensing by Guidance
and Control System). |
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|
Earth |
The third planet
from the sun, having a sidereal period of revolution
about the sun of 365.26 days at a mean distance of
approximately 149 million kilometers (92.96 million
miles), an axial rotation period of 23 hours 56.07
minutes, an average radius of 6,374 kilometers (3,959
miles), and a mass of approximately 5.974 × 1024
kilograms (13.17 × 1024 pounds). |
EFL |
Effective Focal
Length |
Electromagnetic |
Relating to the
interplay between electric and magnetic fields. In
particular, light (as well as x-rays, microwaves,
gamma rays, etc.) is electromagnetic radiation, consisting
of alternating electric and magnetic fileds which
move through space. |
Electromagnetic
Spectrum |
The array of electromagnetic
radiation, arranged in order of wavelength gamma
rays. Also referes to a narrower band of wavelengths,
called the visible spectrum, as when light dispersed
by a prism shows its component colors. Spectra are
often striped with emission or absorption lines,
which can be examinded to reveal the composition
and motion of the light source. |
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Field |
An area in which
a gravitational, electric, or magnetic force occurs. |
Fission |
The splitting of
heavier atomic nuclei into lighter ones. In the case
of heavy atoms (e.g., uranium, plutonium), this will
release energy. Fission is how nuclear power plants
produce energy. |
Fusion |
The combining of
lighter elements into heavier ones. For lighter elements
(e.g., hydrogen, helium) this process releases energy.
Fusion is how stars produce energy, and is being
researched as a way to produce power on Earth. |
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Gamma
Rays |
High energy, very
short wavelength electromagnetic radiation which
can be generated by nuclear reactions (ie., fission
and fusion). |
GEC |
Geospace Electrodynamic
Connections Connections (one of the Solar Terrestrial
Probes missions) |
Geospace |
Also called the
solar terrestrial environment, geospace is the domain
of sun-earth interactions. It consists of the particles,
fields, and radiation environment from the Sun to
Earth's space plasma environment and upper atmosphere.
Geospace is considered to be the fourth physical
geosphere (after solid earth, oceans, and atmosphere). |
Geosynchrononous |
Refers to an orbit
with a period equal to one day. A satellite in geocynchronous
orbit above Earth's equator will stay over the same
point on Earth at all times. Communications satellites
are often put in geosynchronous orbits so that satellite
dishes on earth can remain pointed at the same point
in the sky at all times. |
GPS |
Global Positioning
System |
|
Goddard Space Flight
Center (NASA Center located in Greenbelt, Maryland) |
Gravity |
The force by which
a planet or other such body tends to draw objects
toward its center. |
GUVI |
Global Ultraviolet
Imager (instrument on TIMED from the JHU/APL, Laurel,
Maryland and The Aerospace Corporation, El Segundo,
California) |
Gyroradius |
A charged particle
moving in a magnetic field will orbit around the
magnetic field lines. The radius of this orbit is
called the gyroradius (also know as the Larmor radius).
The gyroradius is larger for faster or more massive
particles and smaller for stronger magnetic fields. |
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Heliosphere |
The vast region
starting at the Sun's surface and extending to the
limits of the solar system, well beyond the orbits
of the most distant planets. |
|
The Hubble Space
Telescope (HST) is a unique astronomical observatory.
From its vantage point 620 km above the surface of
the Earth, it looks out into space with a 2.4 meter
primary mirror which provides unprecedented image
resolution from 120 nm (near-ultraviolet) to 2500
NM (near-infrared). The near vacuum of space affords
the HST with an unfair advantage over ground-based
observatories. The Earth's atmosphere absorbs a great
deal of ultraviolet and infrared radiation, and distorts
visible light images as well. In the upper reaches
of the atmosphere, the HST is able to capture images
and spectra from distant stars which would be difficult
or impossible to obtain from the ground. (NASA satellite) |
Hydrosphere |
The water on or
around the surface of a planet. |
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IMPACT |
In situ Measurements
of Particles And CME Transients (instrument on STEREO
from the University of California, Berkeley) |
Ion,
Ionize |
An ion is an atom
which has lost or gained one or more electrons so
that it has a net electrical charge. Normally atoms
have equal numbers of negatively charged electrons
and positively charged protons so that the total
charge of the atom is zero. |
Ionosphere |
The region of Earth's
atmosphere that extends from about 50 to 300 miles
above the surface of the planet and is made up of
multiple layers dominated by electrically charged
or ionized atoms. |
ISAS |
Institute of Space
and Astronautical Sciences (Japan) |
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|
JHU/APL |
Johns Hopkins University
Applied Physics Laboratory (located in Laurel, Maryland) |
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Lithosphere |
The crust of a planet. |
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Magnetic
Field |
A field of force
around the Sun and the planets, generated by electrical
currents, in which a magnetic influence is felt by
other currents. The Sun's magnetic field, like that
of Earth, exhibits a north and south pole lined by
lines of magnetic force. |
Magnetic
Field lines |
A magnetic field
has both a strength and a direction at each point
in space. For example, at each point on the earth,
the magnetic field -- and thus a compass -- points
a particular direction, roughly toward the North.
Magnetic fields are therefore generally represented
as lines: the direction of the line gives the direction
of the field and the number of lines indicates the
strength. |
Magnetic
Storms
and Substorms |
A series of terrestrial
distrubances -- namely, the precipitation of auroras
and rapid changes in Earth's magnetic field -- caused
by high-speed blasts of the solar wind. Magnetic
storms have measurable effects worldwide, such as
radio communication blackouts and power grid failures.
Magnetic storms are far less frequent than magnetic
substorms which are initiated by processes on Earth's
magnetotail and are restricted to the auroral ovals. |
Magnetopause |
The location in
space where Earth's magnetic field balances the pressure
of the solar wind. It is located about 63,000 km
from Earth in the direction of the Sun, or about
1/6th the distance to the moon's orbit. |
Magnetosphere |
The outermost environment
of Earth, dominated by the Earth's magnetic field.
The magnetosphere is the site of the radiation belt
and many intricate phenomena. See solar
wind. |
Magnetotail |
The region on the
night side of the Earth where the magnetic filed
is stretched backwards by the force of the solar
wind. |
MC |
Magnetospheric Constellation
(one of the Solar Terrestrial Probes missions) |
MLTI |
Mesosphere and Lower
Thermosphere/Ionosphere (the region of the Earths
atmosphere that TIMED is to study) |
MMS |
Magnetospheric MultiScale
(one of the Solar Terrestrial Probes missions) |
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|
National Aeronautics
and Space Administration |
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Perihelion |
The point in the
orbit of a planet, comet etc, which is closest to
the sun. |
Periodic
Table |
An arrangement of
elements in order of increasing atomic numbers that
also emphasizes periodicity. |
Photosphere |
The visible region
of the Sun: above the photosphere are the chromosphere,
then the corona. |
Plasma |
One of the four
states of matter. (The other three are solid liquid
and gas.) Consists of a gas of positively charged
and negatively charges particles with approximately
equal concentrations of both so that the total gas
in approximately charge neutral. A plasma can be
produced from a gas if enough energy is added to
cause the electrically neutral atoms of the gas to
split into positively and negatively charged atoms
and electrons. |
PLASTIC |
PLAsma and SupraThermal
Ion and Composition (instrument on
STEREO from the University of New Hampshire) |
Plumes |
A structure or form
that is like a long feather: a plume of smoke. |
Polar
Cusps (or Cusps) |
The funnel shaped
magnetic field regions located above Earth's magnetic
poles. Solar wind plasma has near direct access to
these regions. |
Prominence |
An eruption of hot
gases above the photosphere of the Sun. Prominences
are most easily visible close to the limb of the
Sun, but some are also visible as bright streamers
on the photosphere. |
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Radiation
Belt |
Magnetized planets,
like Earth, are encircled by zones of particle radiation
known as the " Van Allen belts." in which
charged particles spiral to and fro, trapped by the
planet's magnetic field. |
Radiation |
Energy transmitted
through space as waves or particles. |
Reconnection |
The rejoining of
solar magnetic lines of force severed by the annihilation
of the magnetic field across a neutral zone. |
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SABER |
Sounding of the
Atmosphere using Broadband Emission Radiometry (instrument
on TIMED from
Hampton University, Virginia) |
Satellite,
artificial |
An object launched
by a rocket into orbit around the Earth or, occasionally,
another solar-system body. |
Satellite,
Natural |
A body that revolves
around a larger body; generally, a satellite is a
body in orbit around a planet. However, a satellite
was recently discovered orbiting an asteroid, and
several other asteroid satellites are suspected to
exist. They are often called moons. |
Science
Discovery |
A hands-on science
program at the University of Colorado, Boulder. Each
year, it offers over one hundred after-school and
summer classes and camps, visits classrooms across
the state through a program called Science From CU,
develops hands-on curricula, and conducts the Science
Explorers teacher training workshops in ten locations. |
SEC |
Sun-Earth Connection |
SECCHI |
Sun-Earth Connection
Coronal and Heliospheric Investigation (instrument
on
STEREO from the Naval Research Laboratory, Washington,
DC) |
SEE |
Solar Extreme Ultraviolet
Experiment (instrument on
TIMED from the University of Colorado, Boulder) |
|
Solar and Heliospheric
Observatory (a NASA spacecraft launched on December
2, 1995) |
Solar
Flare |
A rapid outburst
on the Sun, usually in the vicinity of active sunspots.
A sudden brightening (only rarely seen without special
filters, isolating the red light of hydrogen) may
be followed by the signatures of particle acceleration
to high energies--x-rays, radio noise and often,
a bit later, the arrival of high-energy ions from
the Sun. Flares appear to be associated with rapid
energy releases high above the photosphere, apparently
from the magnetic fields of sunspots. Their link
to coronal mass ejections, which may also be powered
by magnetic energy, is still unclear. |
Solar
Wind |
The outflow of charged
particles from the solar corona into space. Because
of the high temperature of the particles of the corona
(mostly protons and electrons), they are moving at
speeds higher than the solar escape velocity. At
the orbit of the Earth, these particles are moving
at about 500 km/sec. Some of these particles are
captured by the magnetic fields of the planets, forming
their magnetospheres. |
Space
Weather |
The conditions and
processes occuring in space which have the potential
to affect the near Earth environment. Space Weather
processes can include changes in the interplanetary
magnetic filed, coronal mass ejections form the sun
and disturbances in the Earth's magnetic field. The
effects can range from damage to satellites to disruption
of power grids on Earth. |
Star |
Hot, incandescent
sphere of gas (usually more than 90% hydrogen) that
is held together by its own gravitation and emits
light and other forms of electromagnetic radiation
whose ultimate source is nuclear energy. The universe
contains billions of galaxies, and each galaxy contains
billions of stars, which are frequently bunched together
in star clusters of as many as 100,000. The stars
visible to the unaided eye are all in our own galaxy,
the Milky Way. The visible stars are divided into
six classes according to their apparent magnitude.
Stars differ widely in mass, size, temperature, age,
and luminosity. About 90% of all stars have masses
between one tenth and 50 times that of the sun. The
most luminous stars (excluding supernovas) are about
a million times more powerful than the sun, while
the least luminous are only a hundredth as powerful.
Variable Stars fluctuate in luminosity. Red giants,
the largest stars, are hundreds of times greater
in size than the sun. At the opposite extreme, white
dwarfs are no larger than the earth, and neutron
stars are only a few kilometers in radius. The central
region, or core, has a temperature of millions of
degrees. At this temperature nuclear energy is released
by the fusion of hydrogen to form helium. By the
time nuclear energy reaches the surface of the star,
it has been largely converted into visible light
with a spectrum characteristic of a very hot body.
The theory of stellar evolution states that a star
must change as it consumes its hydrogen in the nuclear
reactions that power it. When all its nuclear fuel
is exhausted, the star dies, possibly in a supernova
explosion. |
STEREO |
Solar Terrestrial
Relations Observatory (one of the Solar Terrestrial
Probes missions) |
STP |
Solar Terrestrial
Probes (a NASA Program
managed by NASA GSFC) |
Streamers |
An extension of
rays from the sun's corona. |
Sun |
Intensely hot, self-luminous
body of gases (mainly hydrogen and helium) at the
center of the solar system. The Sun is a medium-size
main-sequence star. Its mean distance from Earth
is defined as one Astronomical Unit (AU). The Sun
is about 865,400 miles (1,392,000 km) in diameter;
its volume is about 1,300,000 times, and its mass
332,000 times, that of the Earth. At its center,
the Sun has a density over 100 times that of water,
a pressure of over 1 billion atmospheres, and a temperature
of about 15,000,000 degrees Kelvin. This temperature
is high enough for the occurrence of nuclear reactions,
which are assumed to be the source of the Sun's energy.
The bright surface of the Sun is called the photosphere;
its temperature is about 6000 degrees Kelvin. During
an eclipse of the Sun, the chromosphere (a layer
of rarified gases above the photosphere) and the
corona (a luminous envelope of extremely fine particles
surrounding the Sun, outside the chromosphere) are
observed. |
Sunspot
Cycle |
The recurring, eleven
year rise and fall in the number of sunspots. |
Sunspot |
An area seen as
a dark spot on the photosphere of the Sun. Sunspots
are concentrations of magnetic flux, typically occurring
in bipolar clusters or groups. They appear dark because
they are cooler than the surrounding photosphere. |
Sunspot
Number |
A daily index of SUNSPOT activity
(R), defined as R = k (10 g + s) where S = number
of individual spots, g = number of sunspot groups,
and k is an observatory factor.orA measure of sunspot
activity, computed from the formula R = k (10 g +
f) where R is the relative sunspot number; f is the
number of individual spots; g is the number of groups
of spots; and k a factor that varies with the observer
(his personal equation), the seeing, and the observatory
(location and instrumentation). |
S/WAVES |
STEREO/WAVES (instrument
on STEREO;
a collaborative effort between the Centre National
de La Recherche Scientifique Observatory of Paris,
France and NASA GSFC, Greenbelt, Maryland) |
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TIDI |
TIMED Doppler Interferometer
(instrument on TIMED from the University of Michigan,
Ann Arbor) |
TIMED |
Thermosphere, Ionosphere,
Mesosphere Energetics and Dynamics Mission(one of
the Solar Terrestrial Probes missions) |
TRACE |
Transition Region
and Coronal Explorer (one of the Small Explorer missions
launch in April 1988) |
Transition
Region |
A layer of the solar
atmosphere a few hundred kilometers thick that lies
between the chromosphere and the corona, within which
temperatures rise from about 10,000 to over one million
Kelvin. |
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|
UV |
Ultraviolet |
