The Suns Visible Edge Is An Illusion

Tte entire Sun is just a giant incandescent, gaseous ball that seems to extend forever, tte gas is compressed at its center, becoming progressively more tenuous further out. And being entirely gaseous, the Sun has no solid surface and no permanent visible features. tte specification of a surface that divides the inside of the Sun from the outside is therefore largely a matter of choice, depending on the wavelength that provides the required perspective. At the wavelengths we see with our eye,...

Geomagnetic Storms

Although the gusty solar wind never reaches the Earth's surface, it can cause dramatic changes in the Earth's magnetic field. George Graham (1674-1751), a London watchmaker, first noted the magnetic variation in 1722 as a pronounced swing and rapid fluctuation in the direction that compass needles point. Graham and the Swedish astronomer and physicist Anders Celsius (1701-1744) independently noticed in 1741 that irregular deflections of the compass needle occur when intense auroras are present,...

Author Index

Abbott, Charles Greeley(1872-1973) 213 Adhemar, Joseph Alphonse (1797-1862) 227 Alfven, Hannes (1908-1995) 118 Alighieri, Dante (1265-1321) 234 Anderson, Carl D. (1905-1991) 30, 233 ngstr m, Anders Jonas (1814-1874) 238 Appleton, Edward (1892-1965) 206 Aristotle (384-322 BC) 82, 174 Arrhenius, Svante August (1859-1927) 200, 235, 248 Babcock, Horace W. (1912-2003) 103, 234 Bahcall, John N. (1934-2005) 46, 53, 234 Bailey, Francis (1774-1844) 109, 234, 239 Balmer, Johann (1825-1898) 12, 239...

Energizing the

IMPRESSION OF THE RISING SUN This portrayal of sunrise by the French artist Claude Monet (1840-1926) gave the Impressionist Movement its name. (Courtesy of the Mus e Marmottan, Paris.) tte Sun is extremely massive, containing 99.9 percent of the total mass of the Solar System, tte gravitational pull of the Sun's large mass controls the movements of everything in its vicinity, ttat is the reason the planets belong to the Solar System their motion is dominated by the Sun. Our home star is also...

Info

FIG. 9.10 Varying solar heating ofthe upper atmosphere During the Sun's 11-year activity cycle, the upper-atmosphere temperatures fluctuate by factors of two, and neutral (un-ionized atom) and electron densities by factors of ten. The bold lines (rightside) register maximum values and the less bold (left side) the minimum values. Enhanced magnetic activity on the Sun produces increased ultraviolet and X-ray radiation that heats the Earth's upper atmosphere and causes it to expand, resulting in...

Space Weather

Ttere is danger blowing in the Sun's wind, which contains powerful gusts and squalls, ttey are the cosmic equivalent of terrestrial blizzards or hurricanes. Down here on the ground, we are shielded from this space weather by the Earth's atmosphere and mag netic fields, keeping us from bodily harm. But out in deep space there is no place to hide, and both humans and satellites are vulnerable. tte storms in space can even kill an unprotected astronaut repairing a space station or walking on the...

Magnetic Fields In The Visible Photosphere

Tte sunlight we see coming from the bright disk of the Sun originates in the photosphere, a word derived from the Greek photos for light and sphere for its spherical shape, tte photosphere is a thin tenuous layer, only a few hundred kilometers thick, with a temperature of 5,780 kelvin and a pressure of one ten-thousandth (0.0001) of the pressure of the Earth's atmosphere at sea level. You are looking at the photosphere when you watch the Sun rise in the morning, and continue on its dailyjourney...

Coronal Mass Ejections

Tte most spectacular solar eruptions are gigantic magnetic bubbles, called coronal mass ejections, which expand outward from the Sun (Fig.7.16). A typical coronal mass ejection carries about 10 billion tons, or 10 million million kilograms, of coronal material as it lifts off into space, removing about a tenth of the total coronal mass, tte outward-moving coronal mass ejections stretch the magnetic field until it snaps, leaving behind only bright rays rooted in the Sun. ttey can expand to...

The Eternal Solar Wind

Just half a century ago, most people visualized our planet as a solitary sphere traveling in a cold, dark vacuum around the Sun. But we now know that the wide-open spaces in our Solar System are not empty, ttey are filled with tiny pieces of the Sun, in an ever-flowing solar wind. tte notion that something is always being expelled from the Sun first arose from observations of comet tails. Comets appear unexpectedly almost anywhere in the sky, moving in every possible direction, but with tails...

N

Nanoflares Ubiquitous low-level flares that might heat the corona, also called microflares. ey may be detected at extreme ultraviolet, radio, ultraviolet and X-ray wavelengths. A billion of them would be required to release the same amount of energy as a normal flare. See microflares. NanoTesIa A unit of magnetic field strength, abbreviated nT. It is equal to 10 9 Tesla, to 10 5 Gauss, and to 1 gamma. See Gauss, and Tesla. NASA Acronym for the National Aeronautics and Space Administration,...

Earths Magnetic Cocoon

Report Terrestrial Magnetism

William Gilbert (1544-1603), physician to Queen Elizabeth I (1533-1603) of England, used a spherical magnet, called a terrella, or little Earth, to show why compass needles point north and south. Whenever a compass was placed on the sphere, the needle pointed to its north or south magnetic poles. As suggested by Gilbert in 1600, in his treatise, De magnete magnus magnes ipse est globus terrestris, translated About magnetism the terrestrial globe is itself a great magnet, the Earth has a huge...

Focus

Taking the Temperature of the Corona tte Sun's enormous gravity would hold a relatively cool gas close to the photosphere, just as the Earth's gravity binds its atmosphere into a thin shell. But this is inconsistent with the larger extent of the corona seen during a total solar eclipse. A temperature of a million degrees is required to keep the corona extended the motion of the heated gas supports it against the Sun's gravitational pull. At cooler temperatures, the atoms would have to be much...

Neutrinos From The

Solar neutrinos are produced in profusion by thermonuclear reactions in the Sun's core, removing substantial amounts of energy that is never seen again. When hydrogen is burned into helium, thereby making the Sun shine, four protons are united, but two of them have to be turned into neutrons to make a helium nucleus. Each conversion of a proton into a neutron coincides with the birth of a neutrino so two neutrinos are created each time a helium nucleus is made. To make the Sun's energy at its...

Coronal Heating

More than half a century ago, astronomers knew that the corona is a very hot, rarefied gas. So they knew what the corona is, but not why it exists, tte problem, which has not yet been completely solved, is to explain why the corona is so hot. tte visible solar disk, the photosphere, is closer to the Sun's center than the million-degree corona, but the photosphere is several hundred times cooler, and this comes as a big surprise, tte essential paradox is that energy should not flow from the...

The Ice Is Coming

During the past two million years, huge ice sheets have advanced across the Northern Hemisphere and retreated again more than twenty times, tte great, extended ice sheets last roughly 100,000 years, keeping the climate cold and the sea level low. tte warm periods that punctuate the cold spells have been exceptional, each lasting roughly 10,000 years, tteir scientific name, the interglacials, reflects their unusual nature. tte most recent advance, called the Wisconsin, started about 120,000...

Ingredients Of The

Celestial objects are composed, like the Earth and we ourselves, of individual particles of matter called atoms. But the atoms consist largely of seemingly empty space, just as the room you maybe sitting in appears mostly empty. A tiny, heavy, positively charged nucleus lies at the heart of an atom, surrounded by a cloud of relatively minute, negatively charged electrons that occupy most of an atom's space and govern its chemical behavior. In the early 20th century, the New Zealand-born British...

Quotation References

An incantation from Ptolemaic Egypt (373-30 BC). Quoted by Carl Sagan in Cosmos. Random House, New York 1980, p.217. 2. Friedrich Nietzsche (1844-1900) Wus Spoke Zarathustra - Of Immaculate Perception. Translated by R. J. Hollingdale. Penguin Books, Harmondsworth 1961,p. 146. 3. Francis William Bourdillon (1852-1921) Among the Flowers (1878). In ne Oxford Dictionary of Quotations, Fourth Edition (Angela Partington, ed.). Oxford University Press, New York 1992, p. 138. Also in John Bartlett's...

Convection And Granulation

Radiation streaming out from the Sun's energy-generating core is stopped at the bottom of the convective zone, which occupies the outer 28.7 percent of the solar radius. In this region, the relatively cool, opaque solar gas absorbs great quantities of radiation without re-emitting it. ttis causes the material to become hotter than it would otherwise be, and the Sun must find another way to release the pent-up energy. tte heated material expands, becomes less dense than the gas in overlying...

Northern And Southern Lights

Tte northern and southern lights are one of the most magnificent and earliest-known manifestations of the myriad links between the Sun and the Earth, ttey illuminate the Arctic and Antarctic skies, where curtains of multi-colored light dance and shimmer across the night sky far above the highest clouds, like giant dragons or snakes (Figs. 8.7, 8.8). Perhaps because they can be colored red like the rising morning Sun, they are often called the aurora after the Roman goddess of the rosy-fingered...

The Solar Chromosphere And Its Magnetism

Just above the photosphere lies a thin gaseous layer called the chromosphere, from chromos, the Greek word for color and sphere for its spherical shape, tte chromosphere is so faint that it was first observed during a total eclipse of the Sun. It became visible a few seconds before and after the eclipse, creating a narrow pink, rose or ruby-colored band at the limb of the Sun. tte solar limb is the apparent edge of the photosphere disk as viewed from the Earth during a total solar eclipse the...

The Elusive Neutrino

Neutrinos, or little neutral ones, are very close to being nothing at all. ttey are tiny, invisible packets of energy with no electric charge and almost no mass, traveling at nearly the velocity of light, ttese subatomic particles are so insubstantial, and interact so weakly with matter, that they streak through almost everything in their path, like ghosts that move right through walls. Unlike light or any other form of radiation, the neutrinos can move nearly unimpeded through any amount of...

Storing Invisible Particles Within Earths Magnetosphere

Charged particles flowing from the Sun can enter the Earth's magnetic domain and become trapped within it. ttey can be stored along the stretched dipolar field lines, earthward of the tail magnetic connection site, in a region called the plasma sheet. It acts as a holding tank of electrons and ions, suddenly releasing them when stimulated by the ever-changing Sun. Nearer the Earth particles are stored in the radiation belts, regions of an unexpectedly high flux of high-energy electrons and...