- Active Region:
- A region of the Sun where sunspots, plages, and flares are found.
- Chromosphere:
- The layer of the solar atmosphere that is just above the photosphere and below the corona. It is between about 250 miles (400 km) and 1,300 miles (2,100 km) above the solar surface. The temperature of the chromosphere varies between about 6,700 Fahrenheit (3,700 Celcius) at the bottom and 14,000 Fahrenheit (7,700 Celcius) at the top. In the chromosphere, the temperature actually gets hotter the further you go from the Sun.
- Corona:
- The outermost layer of the Sun. It begins at about 1,300 miles (2,100 km) above the surface and extends far out into space. The temperature in the corona ranges between about 900,000 Fahrenheit (500,000 Celcius) to a few milliion degrees. The corona is an extremely low density region. It can only be seen during a total solar eclipse or with an instrument called a coronagraph.
- Coronagraph:
- An instrument used to view the solar corona at times other than during a total solar eclipse. It creates an artificial eclipse by placing an occulting disk in front of the photosphere and chromosphere of the Sun. This disk blocks the bright light from these regions, allowing the faint light from the corona to be studied.
- Coronal Hole:
- An area in the corona of the Sun that appears dark in pictures taken with coronagraphs or during total solar eclipses. Coronal holes are large regions in the corona that are less dense and cooler than surrounding areas. Coronal holes occur where the magnetic field of the Sun is open, allowing solar plasma to stream into space, creating the solar wind. Coronal holes are often found near the north and south poles of the Sun.
- Coronal Mass Ejection (CME):
- A huge eruption of material from the solar corona into interplanetary space. CMEs often look like bubbles or loops which can grow to extremely large sizes. Coronal Mass Ejections are also called Coronal Mass Eruptions or Coronal Transients.
- Filament:
- A dark structure in the solar corona which has formed above a boundary at the solar surface (photosphere and chromosphere) between large scale magnetic fields of opposite polarity.
- Filament Channel:
- An area along a polarity reversal boundary where a filament can form or has formed.
- Flare:
- See "Solar Flare" below.
- Granulation:
- Convection cells on the Sun. Granulation covers the solar photosphere and is due to hot solar gases being transported by convection. The bright portions of the individual granules are regions where hot gas is rising, and the darker lanes surrounding them are regions where cooler gas sinks.
- Penumbra:
- The lighter, outer portion of a sunspot, in which thread-like light and dark filaments mostly point away from the umbra. These structures are formed by strong magnetic fields.
- Photosphere:
- The deepest layer of the Sun that we can see. This layer reaches from the surface visible in the center of the solar disk to about 500 km above that height. The temperature in the photosphere reaches from about 11,200 Fahrenheit (6,200 Celcius) at the bottom to about 6,700 Fahrenheit (3,700 Celcius) at the top. Almost the whole photosphere is covered with granulation.
- Plage:
- An area on the Sun that is brighter than its surroundings.
- Prominence:
- A filament seen above the limb. (Note: The term "prominence" is often used interchangeably with "filament" and is considered the more generic term. However, the traditional definition for a "prominence" is any solar structure seen above the limb. This includes flare loops and surges, which are dynamic events not included in the definition of a "filament." Here, the names of dynamic events will be used to avoid this confusion with these current definitions.)
- Quiescent Filament:
- A long-lived and relatively stationary filament.
- Quiescent Prominence:
- A long-lived and relatively stationary prominence.
- Quiet Sun:
- Solar phenomena which do not vary with the solar cycle.
- Solar Atmosphere:
- The photosphere, chromosphere and corona of the Sun.
- Solar Cycle:
- The activity on the Sun (number of sunspots, flares, and active regions) varies fairly regularly with a period of about 11 years. This regular variation in activity is called the solar (or sunspot) cycle.
- Solar Flare:
- Solar flares are huge explosions of gas in the solar atmosphere. Solar flares usually occur near active regions. They are characterized by a sudden, intense increase in brightness.
- Solar Wind:
- An outflow of particles from the Sun.
- Spicule:
- A small jet of gas at the edge of the quiet Sun. Spicules are about 600 miles (1,000 km) in diameter and 6,200 miles (10,000 km) high. They usually last for about 15 minutes.
- Sunspot:
- A region on the surface of the Sun where the magnetic field is very strong. Sunspots appear as dark spots on the surface of the Sun, but they are still very hot. Sunspots have temperatures of around 6,300 Fahrenheit (3,500 Celcius), while the surrounding surface of the Sun has a temperature of about 10,000 Fahrenheit (5,500 Celcius). Since sunspots are much cooler than the surrounding solar surface, they appear dark. Sunspots come in a variety of sizes, ranging from hundreds to tens of thousands of miles across (many times larger than the Earth). Scientists measure the total size (area) of all of the sunspots seen on the Sun every day to get a measure of how active the Sun is. Sunspots are not permanent. They appear and disappear on the surface of the Sun.
- Transition Zone:
- The thin region between the chromosphere and the corona.
- Umbra:
- The darker, middle portion of a sunspot. The magnetic field in the umbra is very strong and points almost straight up.
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