| A |
| 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. |
|
| B |
| 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. |
|
| C |
| 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. |
|
| D |
| 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). |
|
| E |
| 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. |
|
| F |
| 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. |
|
| G |
| 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 |
| GSFC |
| 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. |
|
| H |
| 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. |
| Hubble
Space Telescope (HST) |
| 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. |
|
| I |
| 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) |
|
| J |
| JHU/APL |
| Johns Hopkins University
Applied Physics Laboratory (located in Laurel,
Maryland) |
|
| L |
| Lithosphere |
| The crust of a planet. |
|
| M |
| 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. |
| MagnetoHydroDynamics (or
HMD) |
| Just as HydroDynamics is
the study of the motion and dynamics of fluids
such as water, MHD is the study of plasma motion
and dynamics in the presence of a magnetic field. |
| 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. |
| MagCON |
| 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) |
|
| N |
| NASA |
| National Aeronautics and
Space Administration |
|
| P |
| 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. |
|
| R |
| 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. |
|
| S |
| 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 (one
of four themes in the NASA Office of Space Science |
| 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) |
| SOHO |
| 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 under the SEC theme
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 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) |
|
| T |
| 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. |
|
| U |
| UV |
| Ultraviolet |
|
