Glossary of Solar Terms
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Active Region - A region of the Sun's
surface layers that has a large magnetic field and in which
sunspots, flares, and prominences preferentially occur.
Angstrom
- A unit of measure equal to 1 hundred-millionth of a
centimeter.
Baily's Beads - Bursts of light that
appear shortly before and after totality during a solar
eclipse. They are formed when rays of sunlight shine through
the valleys and hills on the limb of the moon and were named
for the British astronomer Francis Baily (1774-1844).
Calcium K Line -
Discovered in the
early 1800's, Calcium was catalogued by Joseph Von
Fraunhofer as one of the wavelengths of light emitted in the
Chromosphere of the sun. Making up only .008 percent of the
sun's mass, calcium ions (missing one electron) emit energy
in the ultraviolet portion of the solar spectrum at 3933nm
(393.3A).
Carrington Rotation
- a period of 27.3 days, representing one full rotation of
the Sun as seen from the Earth. The
use of the numbers began on November 9,
1853 and continue to this day.
Chromosphere - A thin (2000 km) layer of the Sun’s
atmosphere between the photosphere and the corona.
Conduction - The transfer of heat by means of direct
collisions between adjacent atoms, molecules, or ions.
Convection - The process of energy transport in which
heat is carried by hot, rising and cool, falling currents or
bubbles of liquid or gas.
Convection Zone - The outer part of the Sun’s interior
in which convection occurs.
Coronado Filters - The
largest manufacturer of amateur solar observing equipment.
Corona
- The Corona is the Sun's outer atmosphere.
Coronal
Mass Ejections - CME's are huge bubbles of gas threaded
with magnetic field lines that are ejected from the Sun over
the course of several hours.
Density - The mass of a body divided by
its volume.
Diamond
Ring - The last of Baily’s beads, which seems to shine
with special brilliance just before a solar eclipse becomes
total.
Eclipse - The obscuration of the light
from the Sun when the observer enters the Moon’s shadow or
the Moon when it enters the Earth's shadow. Also, the
obscuration of a star when it passes behind its binary
companion.
Eclipse Seasons - The times, separated by about 5 1/2
months, when eclipses of the Sun and Moon are possible.
Eclipse
Year - The interval of time (346.6 days) from one
passage of the Sun through a node of the Moon’s orbit to the
next passage through the same node.
EIT
- The SOHO Extreme ultraviolet Imaging Telescope.
Ellerman
Bombs - Bright pin-points of light often found
in Emerging Flux Regions or on the edges of sunspots where
the magnetic field is breaking the surface. Duration is
around 5 minutes.
Emerging
Flux Region (EFR) - A magnetic area on the sun where a
flux tube is surfacing on the disk. ERF's eventually produce
a bipolar sunspot group.
Emission
Line - A narrow, bright region of the spectrum. Emission
lines are produced when electrons in atoms jump from one
energy level to lower energy level
.
Ephemeral Regions - Small magnetic dipoles which
contain no sunspots.
Fabry- Perot Etalon - A non-absorbing,
multi-reflecting device, similar in design to the Fabry-Perot
interferometer, that serves as a multilayer, narrow-bandpass
filter.
Fabry-Perot
Interferometer - A plane-parallel interferometer that
yields extremely high contrast over a wide range of finesse
values without significantly reducing transmission.
Fibrils
- Comparatively small wisps of hydrogen gas that are similar
to Spicules but last twice as long.
Field
Transition Arches - Fibrils which cross the polarity
inversion line of a bipolar magnetic region.
Filament
- A dark line on the Sun’s surface when a
prominence is seen projected against the solar disk.
Flare
- A brief, sudden brightening of a region of the Sun’s
atmosphere, probably caused by the abrupt release of
magnetic energy. Flares are visible with hydrogen-alpha
filters as bright patches of light, but are best observed in x-ray.
Fusion
- A nuclear reaction in which two nuclei merge to form a
more massive nucleus.
Gamma Ray - The part of the
electromagnetic spectrum having the shortest wavelengths.
Heliocentric - Centered on the Sun. In
the heliocentric model of the solar system, the planets move
about the Sun.
Heliopause - The boundary of the heliosphere, where the
solar wind merges into the interstellar gas
Helioseismology - A technique used to study the internal
structure of the Sun by measuring and analyzing oscillations
of the Sun’s surface layers.
Hydrogen Alpha
Line -
One of the wavelengths of
light emitted in the Chromosphere of the sun at 6563Ǻ
(656.3nm).
Heliosphere - The region of space dominated by the solar
wind and the Sun’s magnetic field.
Infrared - The part of the
electromagnetic spectrum having wavelengths longer than
visible light but shorter than radio waves.
Ion
- An atom from which one or more electrons has been removed.
Ionization - The removal of one or more electrons from
an atom.
Ionosphere - The lower part of the thermosphere of a
planet in which many atoms have been ionized by ultraviolet
solar photons.
Limb - The apparent edge of the disk of
a celestial body.
Limb
Darkening - The relative faintness of the edge of the Sun's
disk (limb) compared with the center of the Sun's disk.
Lyman
Series - A series of absorption or emission lines of
hydrogen lying in the ultraviolet part of the
spectrum.
Magnetotail - The part of the
magnetosphere of a planet stretched behind the planet by the
force of the solar wind
Mass
- A measure of the amount of matter a body contains. Mass is
also a measure of the inertia of a body.
Maunder
Minimum - A period of few sunspots and
low solar activity that occurred between 1640 and 1700.
Mean
Solar Time - Time kept according to the
average length of the solar day.
Moreton Wave - A shock wave on the chromosphere
that is seen expanding outward from large solar flares. They
move over the surface at about 1000 km/sec.
Newton's Rings - Simicircular lines that
appear in astronomical images of the sun. Caused by the
reflection of light between the camera array and the
micro-lens over it, these lines can sometimes be reduced by
lower the magnification.
Photon - A massless particle of
electromagnetic energy
Photosphere - The visible region of the atmosphere of
the Sun or another star.
Plages - bright cloud-like features found around
sunspots that represent regions of higher temperature and
density within the chromosphere.
Pores
- Tiny darke spots under 2500 km in size, that have fairly
short lifetimes.
Prominence - A region of cool gas embedded in the
corona. Prominences are bright when seen above the Sun’s
limb, but appear as dark filaments when seen against the
Sun’s disk.
Quiescent
Prominence
- A long
thin prominence that hangs over the solar limb for days,
weeks or months.
Radiative Zone - The radiative
zone extends 55 percent of the sun's radius from the core.
In this zone, the energy from the core is carried outward
by Photons.
SOHO - The Solar and Heliospheric
Observatory satellite launched December 2, 1995 to study the
Earth-Sun interaction.
Solar Core - The core is the
region where the energy of the Sun is produced. Its
temperature is 15 million degrees Kelvin (27 million degrees
Fahrenheit).
Solar
Flare - An explosive release of solar magnetic energy.
Solar
Motion - The motion of the Sun with respect to the
nearby stars.
Solar
Wind - The hot plasma that flows outward from the Sun.
Spicules
- A hot jet of gas moving outward through the Sun's
chromosphere. Spicules are easily seen covering the sun when
viewing through a hydrogen -alpha filter.
Sprays
- Extremely explosive ejections that take place during a
solar flare at high velocities. In the eyepiece a spray
would look like a strait fast moving jet of gas.
Summer
Solstice - The point on the ecliptic where
the Sun’s declination is most northerly. The time when the
Sun is at the summer solstice, around June 21, marks the
beginning of summer.
Sun
Pillar - falling ice crystals can reflect sunlight and
create an unusual column of light.
Sun
Dogs - Extra images of the Sun created by falling
ice-crystals in the Earth's atmosphere.
Sunspot - A region of the Sun’s photosphere that appears
darker than its surroundings. They occur when a
concentrated portion of the Solar magnetic field well up to
the Photosphere.
Sunspot
Cycle - The regular waxing and waning of
the number of spots on the Sun. The amount of time between
one sunspot maximum and the next is about 11 years.
Sunspot
Group - A cluster of sunspots.
Surges - An ejection from the Sun that takes place
during a solar flare. In the eyepiece, a surge would look somewhat curved
like water splashing from a bowl.
Trace - The Transition Region and
Coronal Explorer is a NASA Small Explorer (SMEX) mission to
image the solar corona and transition region at high angular
and temporal resolution.
Transverse Velocity - The part of
the orbital speed of a body perpendicular to the Sun between
the body and the Sun.
Ultraviolet - The part of the
electromagnetic spectrum with wavelengths longer than X
rays, but shorter than visible light.
Umbra
- The inner portion of the shadow of a body, within which
sunlight is completely blocked.
Umbra
- The dark central portion of a sunspot
Wings
of Hydrogen Alpha -
Wavelengths on the longer
side of Ha emission line are referred to as being in the
"red wing", while wavelengths on the shorter side are in the
"blue wing".
Winter Solstice - The point on
the ecliptic where the Sun has the most southerly
declination. The time when the Sun is at the winter
solstice, around December 22, marks the beginning of winter
Credit: The North Houston and Northern Virginia Astro clubs,
Coronado, Spaceweather.com and NASA's Astronomy Picture of
the Day. Please contact me if you notice errors or
omissions.
