Energetic Solar Activity

Without warning, the relatively calm solar atmosphere can be torn asunder by sudden, catastrophic outbursts of incredible energy, ttese transient brightenings, called solar flares, flood the Solar System with intense radiation from X-rays and extreme-ultraviolet radiation to radio waves, tte powerful flares are easily observed at these invisible wavelengths, where they can briefly dominate the Sun's output and sometimes outshine all other astronomical sources (Fig. 7.1).

FIG. 7.1 Extreme ultraviolet flare An explosion on the Sun sends material out 150 thousand kilometers from the visible edge of the Sun. The emitting gas shines in the extreme ultraviolet emission from hydrogen atoms atl2.16 nanometers, called the Lyman alpha transition. This image shows that the radiation is emitted from numerous long, thin magnetic filaments. It was taken from the Transition Region And Coronal Explorer, abbreviated TRACE. (Courtesy of the TRACE consortium and NASA; TRACE is a mission of the Stanford-Lockheed Institute for Space Research, ajoint program of the Lockheed-Martin Solar and Astrophysics Laboratory, or LMSAL for short, and Stanford's Solar Observatories Group.)

FIG. 7.1 Extreme ultraviolet flare An explosion on the Sun sends material out 150 thousand kilometers from the visible edge of the Sun. The emitting gas shines in the extreme ultraviolet emission from hydrogen atoms atl2.16 nanometers, called the Lyman alpha transition. This image shows that the radiation is emitted from numerous long, thin magnetic filaments. It was taken from the Transition Region And Coronal Explorer, abbreviated TRACE. (Courtesy of the TRACE consortium and NASA; TRACE is a mission of the Stanford-Lockheed Institute for Space Research, ajoint program of the Lockheed-Martin Solar and Astrophysics Laboratory, or LMSAL for short, and Stanford's Solar Observatories Group.)

Solar flares are sudden, rapid outbursts of awesome power and violence, on a scale unknown on Earth, the biggest explosions in the Solar System. In minutes, the disturbance spreads along concentrated magnetic fields, releasing energy equivalent to millions of 100-megaton hydrogen bombs exploding at the same time, and raising the temperature of Earth-sized regions to tens of millions of degrees. Solar flares are therefore hotter than the corona. Sometimes they temporarily go out of control and lose equilibrium, becoming hotter than the center of the Sun for a short period of time.

In another type of energetic solar activity, relatively cool, elongated prominences suddenly and unpredictably open up and expel their contents, defying the Sun's enormous gravity (Fig. 7.2). tte erupting prominences are associated with coronal mass ejections; giant magnetic bubbles that expand as they propagate outward from the Sun to rapidly rival it in size (Fig. 7.3). ttese violent eruptions throw billions of tons of material into interplanetary space, tteir associated shocks accelerate and propel vast quantities ofhigh-speed particles ahead of them.

tte rates of occurrence of solar flares, erupting prominences and coronal mass ejections all vary with the 11-year cycle of magnetic activity, becoming more frequent at sunspot maximum. Truly outstanding flares are infrequent, occurring only a few times a year even at times of maximum solar activity; like rare vintages, they are denoted by their date. Flares of lesser magnitude occur much more frequently; several tens of such events may be observed on a busy day near the peak of the 11-year solar cycle of magnetic activity. Up to five coronal mass ejections can occur daily at the peak of the cycle.

FIG. 7.2 Erupting prominence A gigantic erupting prominence is seen escaping from the Sun in the lower left part of this image, taken at a wavelength of 30.4 nanometers, emitted by singly ionized helium, denoted He II, at a temperature of about 60,000 kelvin. The image also portrays the Sun's upper chromosphere and lower transition region at this temperature, with bright blinkers and even brighter active regions. The Earth inset gives the approximate scale of the image, where the diameter of the Earth is 12,700 kilometers. The image was taken on 1 July 2002 with the Extreme-ultraviolet Imaging Telescope, abbreviated EIT, aboard the SOlar and Heliospheric Observatory, or SOHO for short. (Courtesy of the SOHO EIT consortium. SOHO is a project of international collaboration between ESA and NASA.)

All kinds of solar activity therefore seem to be related to the sudden release of stored magnetic energy, but the exact relation between them is unclear. Large coronal mass ejections can occur together with an eruptive prominence, with a solar flare, or without either one of them. And although the frequency of solar eruptions increases with the number of sunspots, their strength does not necessarily increase, tte most intense solar flares and coronal mass ejections are spread throughout the solar cycle.

Even though we are 150 million kilometers away, we still notice the disrupting effects of solar eruptions. Intense radiation from powerful solar flares can travel to the Earth in just 499 seconds, or about 8 minutes, altering our atmosphere, disrupting long-distance radio communications, and affecting satellite orbits. Very energetic

Was this article helpful?

0 0
Telescopes Mastery

Telescopes Mastery

Through this ebook, you are going to learn what you will need to know all about the telescopes that can provide a fun and rewarding hobby for you and your family!

Get My Free Ebook


Post a comment