Artist concept of space weather showing an active Sun with flares and a CME in the upper right, the Earth in the lower right with types of technology affected by space weather to the lower left; satellites, airplanes, the ISS and ground-based electrical lines.

Studying the Sun-Earth connection.

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Terms and Acronyms

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Science Terms/Definitions
Diagram of the layers of the Sun. The IRIS mission will focus on the outer layers › View larger
IRIS will study the Chromosphere and Transition Region of the sun. Credit: National Solar Observatory
The relatively thin region – five to ten thousand miles tall -- of the solar atmosphere located above the sun's surface. The temperature in the chromosphere rises from 6000 K to about 20,000 K, making it hotter than the photosphere but not as hot as the higher atmosphere, the corona. This base layer of the sun's atmosphere requires more energy to heat than the million degree corona itself and provides all the material to the corona and heliosphere. This region is notoriously tricky to study because one can't easily track the way light moves through it.
The sun's dynamic upper atmosphere. It is filled with plasma, whose movements are governed by the tangle of magnetic fields surrounding the sun. While the sun's surface is 6000K, the corona can reach up to millions of degrees, sparking questions from researchers on what mechanisms heat the atmosphere so dramatically. Solar flares and coronal mass ejections originate in the corona.
Coronal Mass Ejection (CME)
Not to be confused with the intense burst of light that is a solar flare, a CME is a cloud of magnetized solar material that erupts from the sun's atmosphere, the corona, into interplanetary space. CMEs do often occur at the same time as a flare, and scientists currently study how the two phenomena are connected. At their largest, CMEs can contain 10 billion tons of matter, and they can move at speeds of up to 4 million miles an hour. Just after blowing into space, a CME cloud can grow as wide as 30 million miles across, 35 times the diameter of the sun.
Artist's rendition of our Heliosphere traveling through interstellar space. › View larger
Artist's concept of our Heliosphere as it travels through our the Milky Way galaxy. Credit: NASA/Goddard/Walt Feimer
The heliosphere is a bubble that surrounds our entire solar system as it travels through space. It is created by the outflow of particles from the sun called the solar wind, which streams far past the outermost planets, six to nine billion miles away from the sun. Solar particles speed outward from the sun, pushing back the material in the rest of space, known as the interstellar medium.
Interface Region Imaging Spectrograph
The photosphere is the surface layer of the sun that we can see in the visible light range.
The material in the sun and its atmosphere -- as well as the material in the aurora and fluorescent lights -- are all plasmas. Plasma is a state of matter much like solid, liquid and gas. Plasmas are so incredibly hot, that the electrons leave their atoms, making it essentially a gas of charged particles. While uncommon on Earth, 99% of the matter we can see in the universe is made of plasma. The electrical charge strongly affects how the particles move, since the particles are simultaneously governed by, and constantly creating, magnetic fields. For example, in close-up images of solar activity you can see the plasma very clearly following the magnetic field lines. Conversely, as plasma moves, it drags its own magnetic fields along for the ride.
Radiative 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.
The Sun unleashed a powerful flare on Nov 4, 2003 as seen by the Extreme ultraviolet Imager in the 195A emission line aboard the SOHO spacecraft. › View larger
The Sun unleashed a powerful flare on Nov. 4, 2003. The Extreme ultraviolet Imager in the 195 angstrom emission line aboard the SOHO spacecraft captured the event. Credit: SOHO, ESA & NASA
Solar Flares
A great burst of light and energetic particles or radiation due to the release of magnetic energy on the sun. Flares are by far the biggest explosions in the solar system, with energy releases comparable to billions of hydrogen bombs. The energetic particles from the flare travels nearly at the speed of light, and so reaches Earth in less than 20 minutes. The energy is generally absorbed by Earth's atmosphere, which protects humans on Earth, however, the energy can cause radio blackouts on Earth for minutes or, in the worst cases, hours at a time. The radiation from a flare would also be harmful to astronauts outside of Earth's atmosphere. Some, but by no means all, flares have an associated CME.
Solar Wind
The solar wind is the constant stream of solar coronal material that flows off the sun. The solar wind is much less dense than the wind on Earth -- indeed it can be 1000 times less dense than a man-made vacuum on Earth -- but it is much faster, typically moving at speeds of one to two million miles per hour. Indeed, the solar wind is constantly on the move: there is no place within the heliosphere where the solar wind's velocity is zero.
Transition Region
The region of the sun's atmosphere between the chromosphere and the corona. Its exact height and position is not well defined since it represents an intensely variable area where many characteristics of the chromosphere transition to those of the region above. Such transitions include the physical laws that describe movement of the material in each region. For example, in the lower chromosphere the material moves as a typical gas or fluid; above, in the corona, one must take into consideration the magnetic forces that dominate the motion. Like the chromosphere, little understood physical processes in the transition region help heat the plasma of the sun's atmosphere to millions of degrees.