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A
angstrom:
A unit of length equal to one hundred-millionth of a centimeter.
active
region: An area of the solar atmosphere
where the Sun’s magnetic field is concentrated. The concentration
and bipolar nature of the magnetic field results in the formation
of dark areas such as sunspots and bright
areas known as faculae. These regions also
produce flares and plages.
aurora:
Light radiated by ions and atoms in the Earth’s upper atmosphere,
mostly in polar regions, the result of bombardment by energetic
electrically charged particles from the ionosphere and magnetosphere.
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B
bow shock:
The shock wave that flanks the magnetosphere on the day side. It
causes the solar wind flow to slow down and flow around the magnetosphere.
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C
chromosphere:
The part of the Sun's (or another star's) atmosphere between the
photosphere and the corona.
convection:
Circulation of a fluid or gas.
corona:
The Sun’s outer atmosphere, with
a temperature of greater than a million degrees, that gives rise
to the solar wind.
coronal
mass ejection: A vast magnetic blob
of plasma that erupts from the Sun's corona and travels through
space at high speed. Coronal mass ejections may cause intense geomagnetic
storms when they strike the Earth and accelerate vast quantities
of energetic particles in both interplanetary space and the magnetosphere.
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D
disk: The
visible surface of the Sun projected against the sky.
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E
extreme
ultraviolet: Electromagnetic radiation,
invisible to the naked eye, with wavelengths shorter than ultraviolet
radiation and longer than x-rays. These wavelengths are mainly responsible
for the existence of the ionosphere.
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F
facula: Brighter-than-average
regions on the Sun’s surface that typically appear near a group
of sunspots just before the sunspots themselves
appear.
flare: A
sudden outburst of energy from the Sun that occurs near concentrated
magnetic fields (known as active regions)
on the Sun’s visible surface. Flares emit high-energy charged
particles (ions and electrons) and all forms of electromagnetic radiation
into space.
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G
gamma rays:
High-energy electromagnetic radiation,
invisible to the naked eye, with wavelengths shorter than x-rays.
Gamma rays are emitted from the Sun during the most energetic flares
on the solar surface.
gauss:
A unit of magnetic field strength.
geomagnetic
field: The Earth’s magnetic field.
geomagnetic
storm: A worldwide large disturbance
in the Earth’s magnetic field, accompanied by intense auroras
in the northern and southern polar regions and intensifications
of the particle radiation trapped in Earth's magnetosphere (the
Van Allen belts).
granulation:
The cellular structure of the photosphere. "Granules"
are formed by convection, each one is
quite large, about 700 to 1000 km (400 - 600 miles) in diameter.
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H
heliopause:
The outer edge of the heliosphere, where
the solar wind runs into the interstellar medium. At the heliopause,
the pressure of the solar wind balances that of the interstellar medium.
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I
infrared
radiation: Electromagnetic radiation,
invisible to the naked eye, with wavelengths longer than visible
light and shorter than microwaves.
interstellar
Medium: Electrified gas and dust between
the stars.
ionosphere:
The highest region of the Earth’s atmosphere containing free
electrons and ions.
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K
Kelvin (K):
A unit of temperature with a magnitude
equal to that of the degree Celsius, and based on a scale in which
0 K is absolute zero (-273.15 °C). A temperature expressed in
Kelvins is equal to the Celsius temperature minus 273.15.
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L
limb: The
edge of the Sun or planet visible to an observer or instrument.
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M
magnetic
field: A map of the direction and strength
of magnetic forces around any object (such as the Sun or planet) that
is magnetic. Magnetic fields are caused by electric currents in the
Sun.
magnetometer:
A device used to measure the magnetic
fields in space and on the ground, and its changes. For example, a
magnetometer can measure changes caused by solar storms.
magnetopause:
The boundary of the magnetosphere, lying
inside the bow shock, usually about 10 Earth radii toward the Sun.
The solar wind is deflected inside the bow shock to flow around the
magnetopause in the magnetosheath.
magnetosheath:
The region between the bow shock and
the magnetopause, characterized by very turbulent plasma. For Earth,
along the Sun-Earth axis, the magnetosheath is about two Earth radii
thick.
magnetosphere:
The region surrounding a planet within
which the planetary magnetic field is the dominant force on electrically
charged particles that can be trapped within the magnetosphere,
making radiation belts like Earth's Van Allen belts.
magnetotail:
A comet-like extension of a planet’s
magnetosphere formed on the planet’s dark night side by the
interaction of the solar wind and the magnetosphere. It can extend
hundreds of planetary radii away from the Sun.
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N
noctilucent
clouds: Clouds formed at extremely high-altitude
that shine at night. A bit of a mystery, scientists aren't sure why
or how they are formed.
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P
penumbra:
A dark region that surrounds an even darker central area of a sunspot.
photosphere:
The visible portion of the Sun.
plage:
Bright regions of gases with concentrated magnetic fields in the
solar chromosphere. They appear near
groups of sunspots and in the regions surrounding
sunspots that are about to emerge.
plasma:
A low-density gas in which the individual
particles are charged and which contains an equal number of positively
charged ions and negatively charged electrons.
plasmasphere:
A region of the inner magnetosphere
that contains relatively cool (low energy) and dense plasma. This
area can be considered an outer extension of the ionosphere.
prominence:
Complex structures of relatively cool,
dense solar material that extend into the outer chromosphere and
inner corona. They are generally static and believed to be supported
by magnetic forces. They can appear as loops on the edge of the
solar disk or limb. Their shape is probably controlled by the Sun's
magnetic field. Sometimes they erupt, often in association with
coronal mass ejections.
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R
radiation:
Radiation has two different meanings. One is the stream of particles
emitted by decaying nuclei such as uranium. This energy often takes
the form of alpha or beta particles, or neutrons. A second use is
as part of the term “electromagnetic radiation," which
refers to energy traveling in the form of electromagnetic waves
or photons. For example, yellow light is a form of electromagnetic
radiation, as are radio waves and x-rays.
radiation
belts: Regions of of high-energy particles
traped by the magnetic influence of the Earth. These belts are sometimes
called "Van Allen" belts because of their discovery in
1958 by Professor J.A. Van Allen. Radiation belts are composed of
electrons, protons, and smaller numbers of other ions.
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S
solar
activity: Activity of sunspots, flares
and CME's which follow the solar cycle.
solar
cycle: A predictable 11-year cycle
when defined by solar activity, including the number of sunspots,
flares, and CMEs, which follow this cycle. When defined by the solar
magnetic field directions, the cycle is 22 years long.
solar
flare: An explosive release of energy
of the Sun.
solar
maximum: A period of increased solar
activity when the number of sunspots reaches a maximum in the 11-year
solar cycle.
solar
minimum: A period of decreased solar
activity when the number of sunspots reaches a minimum in the 11-year
solar cycle.
solar
wind: The charged particles (plasma),
primarily protons and electrons, that are continuously emitted from
the Sun and stream outward throughout the solar system at speeds
of hundreds of kilometers per second.
sunspot:
A region of the solar surface that
is dark and relatively cool; it has an extremely high magnetic field.
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U
ultraviolet
radiation: Electromagnetic radiation,
invisible to the naked eye, with wavelengths shorter than violet
light and longer than x-rays.
umbra:
The dark central area of a sunspot.
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W
white light:
Electromagnetic radiation composed of all wavelengths of light that
is visible to the naked eye (red through violet).
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X
x-rays: High-energy
electromagnetic radiation, invisible to the naked eye, with wavelengths
shorter than ultraviolet radiation and longer than gamma rays. |
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