Sun Causes Space Weather

Ever-Changing Sun Causes Space Weather

Inside the fiery core of the Sun, immense pressures and high temperatures cause the plasma to release incredible amounts of energy, mostly in the form of high energy gamma rays. This reaction is called nuclear fusion.

The incredible energy produced in the Sun's core which began as gamma rays is slowly transformed into sunlight as it moves toward the Sun's surface. The outer layer of the Sun, called the corona, emits a stream of plasma called the solar wind that buffets the entire solar system. (Illustration of the Sun's layers courtesy of the Space Physics Division/NASA.)

Sunspots: Cool, Dark and Magnetic

Appearing in groups that last from several hours to several months,

sunspots are darker, cooler regions of the Sun's photosphere (visible surface), containing intense magnetic fields. Sunspots appear dark because they are cooler than the plasma surrounding them. (Photo at left courtesy of the Space Environment Center/NOAA.) An increase in the number of sunspots signals an increase in the Sun's magnetic activity which reaches a peak about every 11 years. The increase and decrease in the number of sunspots, called the sunspot cycle, has been measured reliably for the last 300 years.

Low sunspot activity might mean lower temperatures. During one seventy-five year period,

"Skating/Frozen River" was painted by Hendrick Avercamp (1585 - ca. 1663) and portrays the cold winter conditions in western Europe at the time.

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. The next solar maximum is due in about 2001.

Solar Flares: The Most Explosive Solar Events

Like pools of gasoline suddenly ignited, solar flares explode as bright flashes above or near cooler sunspot regions in the photosphere. Some flares extend upward more than 60,000 miles into the corona. (Photo courtesy of National Optical Astronomy Observatories.)

Though flares last from only a few minutes to a few hours, they are among the most powerful events in the solar system.

We still do not really understand why and how magnetic energy is released so suddenly and explosively in flares.

The Corona: The Sun's Crown

The Sun's corona is most familiar as the luminous white halo that surrounds the shadowed Sun during a total eclipse. The corona is a realm of superheated plasma, with tapered streamers reaching millions of miles into interplanetary space. The plasma in the corona has a temperature of several million degrees

Centigrade. (Photograph of an eclipse courtesy of Steve Albers.)

The solar wind originates in areas of the corona called coronal holes. In this X-ray photogragh, coronal holes appear black. The bright areas are called active regions. (Photo courtesy of the Lockheed Palo Alto Research Labs and the National Astronomical Observatory in Japan.)

There's More to the Sun than Meets the Eye

Every object in the universe emitting radiation has its own spectrum. Each is unique, like fingerprints.

The Sun's outer layers emit characteristic waves that travel through space at the speed of light (186,000 miles per second). Our Sun's electromagnetic spectrum represents this array of electromagnetic radiation from long-wavelength radio emissions to short-wavelength gamma rays. The most familiar electromagnetic wave is ordinary light, which is itself composed of different electromagnetic wavelengths corresponding to different colors.

Scientists use many parts of the electromagnetic spectrum to study the Sun's layers. In this composite photograph, visible light comes from the photosphere (left image) while X-rays come from the corona (right image). (Photo courtesy of the Lockheed Palo Alto Research Labs and the National Astronomical Observatory in Japan.)