Schematic view of the inner structure of the Sun Click on image for full size (108K GIF) Image courtesy NASA.

Our Sun is the central character in the drama of space weather. Let's take a closer look at the nearest star.

Parts of the Sun

Since the Sun is a giant, seething ball of hot plasma, the boundaries between its regions are necessarily nebulous. The photosphere, the visible "surface" of the Sun, defines the outermost boundary of the "inside" of the Sun. The three main regions of the solar interior are the core (where the nuclear fusion that produces the Sun's energy takes place), the radiative zone, and the uppermost convective zone. The solar atmosphere, extending upward from the photosphere, includes the chromosphere and the extensive corona. The Sun's atmosphere, in the form of the solar wind and the Interplanetary Magnetic Field (IMF), extends outward into interplanetary space. In a sense, the Sun's atmosphere actually fills the heliosphere, the vast "bubble" in space extending well beyond Pluto where the influence of particles from the Sun dominates the influence of the matter that makes up interstellar space.

Solar Features and Phenomena

The Sun is a dynamic star, and its surface and atmosphere are constantly changing. Regions of intertwined magnetic fields arise in the solar interior, bubble up to the photosphere, and give rise to active regions, sunspots, and coronal holes at the Sun's visible surface. Fountains of electrified plasma shoot forth from the photosphere and dance along the lines of magnetic force fields, giving rise to prominences, helmet streamers, spicules, and similar phenomena. Tremendous explosions on the Sun, solar flares and Coronal Mass Ejections (CME), hurl radiation and energized subatomic particles outward into the Solar System.

The Solar Wind

The solar wind is an extension of the Sun's atmosphere into interplanetary space. This supersonic flow of plasma, primarily individual protons and electrons, continuously carries matter and energy outward from the Sun. The IMF, embedded within the solar wind, forms a spiral as it carries the Sun's magnetic force field outward through the Solar System. Interactions between the solar wind and the magnetospheres, atmospheres, and in some cases the surfaces of planets influence the evolution of planets and their atmospheres. The "strength" and nature of the solar wind varies over time, with time scales of the fluctuations lasting hours or days for intense storms to years for variation across the 22-year solar cycle to billions of years for changes throughout a star's lifetime.

The Changing Sun

Though we take the constancy of our Sun for granted, Sol is a dynamic entity. The shifting granulation of the photosphere betrays the roiling convection from below, while prominences and streamers leap through the solar atmosphere along magnetic force fields. Vast explosions, flares and CMEs, alter the Sun's radiation and solar wind over time scales from minutes to hours to days. The 11-year sunspot cycle beats out a longer term and more rhythmic tune of solar variance as the level of solar activity rises and recedes. Studies of Sun-like stars of various ages have helped us learn about our Sun's wild youth and the changes in activity to expect throughout a star's lifetime.

Schematic view of the inner structure of the Sun Click on image for full size (108K GIF) Image courtesy NASA.

Our Sun is the central character in the drama of space weather. Let's take a closer look at the nearest star.

Parts of the Sun

Since the Sun is a giant, seething ball of hot plasma, the boundaries between its regions are necessarily nebulous. The photosphere, the visible "surface" of the Sun, defines the outermost boundary of the "inside" of the Sun. The three main regions of the solar interior are the core (where the nuclear fusion that produces the Sun's energy takes place), the radiative zone, and the uppermost convective zone. The solar atmosphere, extending upward from the photosphere, includes the chromosphere and the extensive corona. The Sun's atmosphere, in the form of the solar wind and the Interplanetary Magnetic Field (IMF), extends outward into interplanetary space. In a sense, the Sun's atmosphere actually fills the heliosphere, the vast "bubble" in space extending well beyond Pluto where the influence of particles from the Sun dominates the influence of the matter that makes up interstellar space.

Solar Features and Phenomenon

The Sun is a dynamic star, and its surface and atmosphere are constantly changing. Regions of intertwined magnetic fields arise in the solar interior, bubble up to the photosphere, and give rise to active regions, sunspots, and coronal holes at the Sun's visible surface. Fountains of electrified plasma shoot forth from the photosphere and dance along the lines of magnetic force fields, giving rise to prominences, helmet streamers, spicules, and similar phenomena. Tremendous explosions on the Sun, solar flares and Coronal Mass Ejections (CME), hurl radiation and energized subatomic particles outward into the Solar System.

The Solar Wind

The solar wind is an extension of the Sun's atmosphere into interplanetary space. This supersonic flow of plasma, primarily individual protons and electrons, continuously carries matter and energy outward from the Sun. The IMF, embedded within the solar wind, forms a spiral as it carries the Sun's magnetic force field outward through the Solar System. Interactions between the solar wind and the magnetospheres, atmospheres, and in some cases the surfaces of planets influence the evolution of planets and their atmospheres. The "strength" and nature of the solar wind varies over time, with time scales of the fluctuations lasting hours or days for intense storms to years for variation across the 22-year solar cycle to billions of years for changes throughout a star's lifetime.

The Changing Sun

Though we take the constancy of our Sun for granted, Sol is a dynamic entity. The shifting granulation of the photosphere betrays the roiling convection from below, while prominences and streamers leap through the solar atmosphere along magnetic force fields. Vast explosions, flares and CMEs, alter the Sun's radiation and solar wind over time scales from minutes to hours to days. The 11-year sunspot cycle beats out a longer term and more rhythmic tune of solar variance as the level of solar activity rises and recedes. Studies of Sun-like stars of various ages have helped us learn about our Sun's wild youth and the changes in activity to expect throughout a star's lifetime.

Schematic view of the inner structure of the Sun Click on image for full size (108K GIF) Image courtesy NASA.

Scientists have named the parts of the Sun. The "surface" of the Sun is called the photosphere. The three areas inside the Sun are called the core, the radiation zone, and the convection zone. You can see these parts on the picture to the left.

The Sun has an atmosphere just like Earth. The Sun's atmosphere is the part that goes out from the "surface" into space. The Sun's atmosphere is much bigger then the Earth's though - it goes all the way out past Pluto!

Solar Features

The Sun is a changing star. It has spots on it that change. They are called sunspots. The Sun also shoots forth material sometimes. Some of these explosions look like loops and some look like streamers shooting out into space.

The Solar Wind

There is also a solar wind that comes from the Sun. It carries with it a magnetic force from the Sun. This force has an effect on planets and moons through the Solar System.