of Space Weather-Related Terms
Glowing, dancing curtains of light in the
upper atmosphere of a planet. Auroras are
caused by the interaction between the planet’s
magnetic field and
charged particles from Earth’s magnetosphere. Aurora Borealis are the
Northern Lights and Aurora Australis are the Southern Lights.
Oval: The ring-shaped belts of auroral
activity around the north and south magnetic
poles. The auroral oval expands and contracts
over a period of hours and days, depending
on geomagnetic activity.
Auroral Substorms: They are caused by streams of charged particles in the magnetotail that are accelerated to high energies and collide with atoms in the upper atmosphere surrounding Earth's poles. This interaction causes the beautiful and eerie looking aurora.
Chromosphere: The irregular layer of the solar atmosphere
that is located above the photosphere and
beneath the corona. The temperature in
the chromosphere rises from 6000° C
to about 20,000° C. It is hotter than
the photosphere but not as hot as the corona.
At these higher temperatures hydrogen emits
light that gives off a reddish color (called
H-alpha emission). This colorful emission
can be seen in prominences that project
above the surface of the Sun during total
solar eclipses. This is what gives the
chromosphere its name (color-sphere). The
chromosphere also produces most of the
UV light from the Sun.
Zone: In the convective zone, rising and
falling currents carry heat from the radiative
zone to the surface. This nonstop churning
is similar to what happens when you boil
water on a stove.
Core: The innermost part of the Sun. The core
produces colossal amounts of energy, including
all of the Sun's light and heat. The temperature
and pressure are so great in the Sun’s
core that hydrogen atoms are squeezed together
to form helium. This reaction is called
nuclear fusion. The temperature at the
center of the Sun is about 15,000,000 °C
(27,000,000 °F) and the density is
about 10 times that of gold or lead.
Corona: The very hot outer layer of the Sun's atmosphere,
composed of highly diffused, superheated,
ionized gases, and extending into interplanetary
space. Some of the hot gasses in the solar
corona escape the Sun to form the solar
Coronal Hole: An area of the corona which appears dark in X-rays and ultraviolet
light. They are usually located at the poles of the Sun, but can occur in other
places as well. The magnetic field lines in a coronal hole extend out into
the solar wind rather than coming back down to the Sun's surface as they do
in other parts of the Sun.
Coronal Mass Ejection (CME):
High speed coronal mass ejections produce
major disturbances in the solar wind.
Often loop-like in appearance, coronal mass ejections rise as massive clouds
of material from the solar atmosphere. Dangerous, high energy, charged particles
are often produced in these disturbances and, when they are directed towards
Earth, often produce large magnetic storms in the magnetosphere.
Cosmic Ray: High energy charged particles traveling through interstellar
space at nearly the velocity of light. Most are produced in supernova explosions.
Electromagnetic Spectrum: The entire range of all the various kinds or wavelengths
of electromagnetic radiation or light, including (from long to short wavelengths):
radio, infrared, visible, ultraviolet, X-rays and gamma rays.
Electron: A sub-atomic particle that has a negative
Filament: A structure in the corona consisting of
cool plasma supported by magnetic fields.
Filaments are dark structures when seen
against the bright solar disk, but appear
bright when seen over the solar limb. Filaments
seen over the limb are also known as prominences.
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.
Geosynchronous: Refers to an orbit (about 22,300 miles
above Earth’s surface) with a period
equal to one day. A satellite in geosynchronous
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.
Heliosphere: A huge magnetic bubble containing the solar wind and the entire
solar magnetic field. At the outermost boundary of the heliosphere, our solar
wind meets the interstellar medium, a plasma that permeates our Milky Way galaxy.
Scientists estimate that this boundary is between 9 and 15 billion kilometers
away from the Sun, far beyond the orbits of all the planets. We should find
out for certain sometime in this century when one or more spacecraft -
Voyagers 1 and 2 and Pioneers 10 and 11 - leave the heliosphere and enter interstellar
Infrared Radiation: Infrared (IR) radiation is electromagnetic radiation whose wavelength is longer than that of visible light, but shorter than microwaves. The name means "below red".
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.
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.
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
linked 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 Earth, the magnetic
field -- and thus a compass -- points in 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.
Storms and Substorms: A series of terrestrial
disturbances – 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 (also
called auroral substorms) which are initiated
by processes in Earth's magnetotail and
are restricted to the auroral ovals.
Magnetosphere: The solar wind pushes and stretches Earth's magnetic field into a vast, comet-shaped region called the magnetosphere. The magnetosphere and Earth's atmosphere protect us from the solar wind and other kinds of solar and cosmic radiation.
Magnetotail: The long magnetic tail of a magnetosphere drawn out by the flow
of the solar wind. Earth’s magnetotail is located on its night side (in
the direction away from the Sun). It extends 100 of thousands of kilometers
and is a major energy source for the magnetosphere.
Maunder Minimum: During one seventy-five year period, now called the Maunder
Minimum (1645-1715), Sunspot activity virtually ceased, and temperatures fell
enough to cause a "Little Ice Age" of severely cold weather across
the northern hemisphere of Earth. During the 11th and 12th centuries, there
was also a large warming coincident with enhanced solar activity.
Photosphere: The photosphere is what our eyes perceive as the visible surface
of the Sun. Here, energy escapes from the interior and streams into the
Sun's atmosphere and beyond. The photosphere is home to dark Sunspots.
Plasma: One of the four states of matter. (The
other three are solid, liquid and gas.)
Plasma is very hot gas that conducts electricity and responds to electric and magnetic forces.
The Sun is made almost entirely of plasma.
This form of matter is rare on Earth (it's
in candle flames, neon signs, fluorescent
lights) but incredibly common in outer
space — 99% of what we can see in the universe
is plasma. Plasma
consists of a gas of positively charged
and negatively charged particles with approximately
equal concentrations of both so that the
total gas is approximately charge neutral.
Prominences: A structure in the Sun’s corona consisting
of cool plasma supported by magnetic fields.
Prominences are dark structures when seen
against the bright solar disk, but appear
bright when seen over the solar limb. Prominences
seen against the disk of the Sun are also
known as filaments. The most recognizable
prominences appear as huge arching columns
of gas above the limb of the Sun. Like
Sunspots, prominences are cooler (about
10,000 °C) in relation to the much hotter
background of the Sun’s outer atmosphere
(about 1,500,000 °C). Prominences can also
erupt from the Sun with tremendous energy.
Proton: A sub-atomic particle that has a positive
electric charge. It is 1836 times more
massive than an electron.
Radiation: Energy transmitted through space as waves
Belt: Magnetized planets, like Earth, are
encircled by zones of particle radiation
known as the "Van Allen belts," in
which high-energy charged particles spiral to and fro,
trapped by the planet's magnetic field.
Zone: In the radiative zone, energy from
the core slowly travels outward. This region
is so dense that the Sun's energy takes
about 150,000 years to work its way through.
Cycle: The approximately 11-year period
during which the frequency and number of
Sunspots, coronal mass ejections, solar
flares, and other solar activity rises
and falls. Also called the Sunspot cycle.
Eclipse: The passing of the Moon between
the Sun and Earth. In a total solar eclipse,
the Moon blocks all light from the solar
disk, allowing us to see the solar corona
Flare: An explosive release of electromagnetic
radiation and huge quantities of charged
particles from a small area of the solar
surface. Solar flares are marked by a sudden
brightening near a Sunspot or prominence.
The radiation released includes X-rays
and radio waves. Solar flares and CMEs
often occur together, but what connections
may exist between them is a matter of debate.
Maximum: The month(s) during the 11-year
solar cycle when the number of Sunspots
reaches a maximum.
Minimum: The month(s) during the 11-year
solar cycle when the number of Sunspots is
System: The Sun and the family of objects
that orbit it. The Solar System includes
things like planets, moons, comets and
asteroids, and a mysterious form of matter called a plasma.
Wind: A continuous stream of tiny charged
particles coming from the Sun. The solar
wind interacts with the magnetic field
and atmosphere of Earth causing auroras.
The solar wind pours out of the Sun at
200 tons per second and a million miles
Weather: The conditions and processes occurring
in space which have the potential to affect
the near Earth environment. Space Weather
processes can include changes in the interplanetary
magnetic field, coronal mass ejections
from the Sun, and disturbances in Earth's
magnetic field. The effects of space weather
can range from damage to satellites to
disruption of power grids on Earth.
Spectrum: Electromagnetic radiation arranged in order
of wavelength from Ion wavelength radio waves to short wavelength gamma rays. A rainbow is a natural spectrum
of visible light from the Sun. Spectra
are often punctuated by emission or absorption
lines, which can be examined to reveal
the composition and motion of the radiating
Sunspot: A dark, fringed blemish on the solar surface
caused by a concentration of the Sun's
magnetic field. Sunspots look dark because
they are cooler than the plasma surrounding
them. Sunspots appear in groups and last
from several hours to several months. The
number of Sunspots increases and decreases
over an eleven-year cycle called the solar cycle. Some individual
spots cover areas 20 times the diameter
Cycle: The recurring, eleven-year rise
and fall in the number of Sunspots.
X-rays: The part of the electromagnetic spectrum
whose radiation has much greater frequencies
and smaller wavelengths than those of ultraviolet
radiation. Because X-rays are absorbed
by the Earth's atmosphere, X-ray astronomy
is performed in space.