sundance

Midsummer 2009

The Sun is the closest star to Earth. The Sun is a huge mass of hot, glowing gas. The strong gravitational pull of the Sun holds Earth and the other planets in the solar system in orbit. The Sun's light and heat influence all of the objects in the solar system and allow life to exist on Earth. The Sun is about 4.6 billion years old and will keep shining for about another 7 billion years.

the most recent complete 11-year sunspot cycle

As Earth turns, the Sun rises over the eastern horizon in the morning, passes across the sky during the day, and sets in the west in the evening. This movement of the Sun across the sky marks the passage of time during the day. The Sun's movement can produce spectacular sunrises and sunsets under the right atmospheric conditions. At night, reflected sunlight makes the Moon and planets bright in the night sky.

The Sun provides Earth with vast amounts of energy every day. The oceans and seas store this energy and help keep the temperature of Earth at a level that allows a wide variety of life to exist. Plants use the Sun's energy to make food, and plants provide food for other organisms. The Sun's energy also creates wind in Earth's atmosphere. This wind can be harnessed and used to produce power.

While it lights our day and provides energy for life, sunlight can also be harmful to people. Human skin is sensitive to ultraviolet light emitted from the Sun. Earth's atmosphere blocks much of the harmful light, but sunlight is still strong enough to burn skin under some conditions. Sunburn is one of the most important risk factors in the development of skin cancers, which can be fatal. Sunlight is also very harmful to human eyes. A person should never look directly at the Sun, even with sunglasses or during an eclipse. The Sun influences Earth with more than just light. Particles flowing from the Sun can disrupt Earth's magnetic field and disrupt electronic communications.

The Sun is large and massive compared to the other objects in the solar system. The Sun's radius is 432,169 miles, 109 times as large as Earth's radius. If the Sun were hollow, a million Earths could fit inside it. The Sun has a mass of 1.989 X 1027 metric tons. Written out, it would be the digits 1989 followed by 24 zeroes. The Sun is 333,000 times as massive as Earth. Despite its large mass, the Sun has a lower density, or mass per unit volume, than Earth. The Sun's average density is only 1.188 oz/cu in, which is a quarter of the average density of Earth. The Sun produces an enormous amount of light. It generates 3.83 ¥ 1026 watts of power in the form of light. In comparison, an incandescent lamp emits 60 to 100 watts of power. The temperature of the outer, visible part of the Sun is 9900 degrees Fahrenheit.

From Earth the Sun looks small because it is far away. Its average distance from Earth is 93 million miles. Light from the Sun takes about eight minutes to reach Earth. This light is still strong enough when it reaches Earth, to damage human eyes when viewed directly. The Sun is much closer to Earth than any other star. he Sun's nearest stellar neighbour Proxima Centauri (part of the triple star Alpha Centauri), is 4.3 light-years from our solar system, meaning light from Proxima Centauri takes 4.3 years to reach the Sun. The Sun is so much closer to Earth than all other stars are that the intense light of the Sun keeps us from seeing any other stars during the day.

Earth would not have any life on it without the Sun’s energy, which reaches Earth in the form of heat and light. This energy warms our days and illuminates our world. Green plants absorb sunlight and convert it to food, which these plants then use to live and grow. In this process, the plants give off the oxygen that animals breathe. Animals eat these plants for nourishment. All plant and animal life relies on the Sun's presence. The Sun also provides - directly or indirectly - much of the energy on Earth that people use for fuel. Devices called solar cells turn sunlight into electricity. Sunlight can heat a gas or liquid, which can then be circulated to heat the building. The energy stored in fossil fuels originally came from the Sun. Ancient plants used sunlight as fuel to grow. Animals consumed these plants. The plants and animals stored the energy of sunlight in the organic material that composed them.

When the ancient plants and animals died and decayed, this organic material was buried and gradually turned into the petroleum, coal, and natural gas people use today. The Sun’s energy produces the winds and the movements of water that people harness to produce electricity. The Sun heats Earth’s oceans and land, which in turn heat the air and make it circulate in the atmosphere as wind. The Sun fuels Earth’s water cycle, evaporating water from the oceans, seas, and lakes. This water returns to the ground in the form of precipitation, flowing back to the oceans through the ground and in rivers. The energy of water’s motion in rivers can be harnessed with dams.

The Sun’s gravitational pull holds the solar system together. The planets, asteroids, comets, and dust that make up our solar system are strongly attracted to the Sun’s huge mass. This gravitational attraction keeps these bodies in orbit around the Sun. The Sun also influences the solar system with its diffuse outer atmosphere, which expands outward in all directions. This expanding atmosphere fills the solar system with a constant flow of tiny, fast, electrically charged particles. This flow is called the solar wind. The region through which the solar wind blows is called the heliosphere. The heliosphere extends outward from the Sun to about 150 times the distance between Earth and the Sun. Interstellar winds may give the heliosphere an egg shape. The solar wind spreads out as it leaves the Sun. The heliopause is the point where the solar wind is so diffuse that it stops having an effect on its surroundings.

Within the heliosphere, the Sun provides most of the heat and light that are present, and the particles in the solar wind interact with the planets and satellites in the solar system. The solar wind causes auroras - displays of coloured light in the atmosphere of Earth’s polar regions. The solar wind also carries remnants of the Sun’s magnetic field, which affect the magnetic fields of the planets and larger satellites. The solar wind pushes the planets¹ magnetic fields away from the Sun, turning them into elongated, windsock shapes.

The Milky Way Galaxy contains about 100 billion stars. All of these stars, and the gas and dust between them, are rotating about a galactic centre. Stars that are farther away from the centre move at slower speeds and take longer to go around it. The Sun is located in the outer part of the galaxy, at a distance of 1.6 ¥ 1017 miles from the centre. The Sun, which is moving around the centre at a velocity of 140 miles per second takes 250 million years to complete one trip around the centre of the galaxy. The Sun has circled the galaxy more than 18 times during its 4.6-billion-year lifetime.

The Sun is extremely important to Earth and to our solar system, but on the scale of the galaxy and the universe, the Sun is just an average star. It is one of hundreds of billions of stars in our galaxy, the Milky Way, which is just one of more than 100 billion galaxies in the observable universe. A star is a ball of hot, glowing gas that is hot enough and dense enough to trigger nuclear reactions, which fuel the star. The Sun is a perfectly ordinary star that behaves exactly the way expected of a star its size. The main difference between the Sun and other stars is that the Sun is much closer to Earth.

Most stars have masses similar to that of the Sun. The majority of stars’ masses are between 0.3 to 3.0 times the mass of the Sun. Theoretical calculations indicate that in order to trigger nuclear reactions and to create its own energy - that is, to become a star - a body must have a mass greater than 7 percent of the mass of the Sun. Astronomical bodies that are less massive than this become planets or objects called brown dwarfs. The largest accurately determined stellar mass is of a star called V382 Cygni and is 27 times that of the Sun.

The range of brightness among stars is much larger than the range of mass. Astronomers measure the brightness of a star by measuring its magnitude and luminosity. Magnitude allows astronomers to rank how bright, comparatively, different stars appear to humans. Because of the way our eyes detect light, a lamp ten times more luminous than a second lamp will appear less than ten times brighter to human eyes. This discrepancy affects the magnitude scale, as does the tradition of giving brighter stars lower magnitudes. The lower a star¹s magnitude, the brighter it is. Stars with negative magnitudes are the brightest of all.

Magnitude is given in terms of absolute and apparent values. Absolute magnitude is a measurement of how bright a star would appear if viewed from a set distance away. By convention, this distance is 10 parsecs, or 32.6 light-years. Apparent magnitude measures how bright a star appears from Earth. The Sun¹s absolute magnitude is 4.8. The brightest known stars have absolute magnitudes of about -9 (lower magnitudes mean brighter stars), and the dimmest known stars have absolute magnitudes of about 20. The apparent magnitude of the Sun is -26.72. The apparent magnitude of the brightest star in Earth¹s night sky, Sirius, is -1.46. The dimmest stars that can be seen from Earth with unaided eyes have apparent magnitudes of about 6.

Astronomers also measure a star’s brightness in terms of its luminosity. A star's absolute luminosity or intrinsic brightness is the total amount of energy radiated by the star per second. Luminosity is often expressed in units of watts. The Sun's absolute luminosity is 3.86 ¥ 1026 watts. The absolute luminosity of stars ranges from one thousandth of the luminosity of the Sun to 10 million times that of the Sun.

Another way of measuring brightness is to measure the amount of light that reaches an observer. This measurement is called apparent brightness or apparent luminosity. Apparent luminosity depends on the absolute luminosity of a star and the distance from the star to the observer. Apparent luminosity becomes smaller as distance from the star to the observer becomes larger. From Earth, the apparent luminosity of the Sun is 10 billion times greater than the apparent luminosity of the next brightest star, Sirius, because the Sun is so much closer to Earth.

The radius of the Sun is about average among stars. The radii of most stars fall between 0.2 and 15 times the Sun¹s radius, although some giant stars are hundreds of times larger than the Sun. Larger stars usually have larger absolute luminosities. We receive much more energy from the Sun than from other stars, because the Sun is so nearby. The Sun's proximity also allows scientists to study its face in detail. A modest telescope can resolve solar structures that are 400 miles across - about the distance from Boston, Massachusetts, to Washington, DC That level of detail is comparable to seeing the features on a coin from half a mile away. Other stars are so distant that the details on their surfaces remain unresolved with even the largest telescopes.

 

 

The Sun is a second-generation star, its material coming from former stars. Some stars are nearly as old as the expanding universe assumed to originate in the Big Bang about 15 billion years ago. Our Sun, in contrast, is only 4.6 billion years old. First generation stars were composed of hydrogen and helium. Second generation stars, like the Sun, have hydrogen as their main ingredient but also contain heavier elements like carbon, nitrogen, and oxygen formed inside first-generation stars that lived and died before the Sun was born. When these massive, short-lived stars used up their internal fuel, they exploded and ejected the heavier elements into interstellar space. The Sun formed from this material.

Measuring the speed of sound waves in the Sun helps determine the temperature and composition of the Sun. The speed of sound depends on the temperature and composition of the material through which the sound passes. Helioseismologists employ this relationship to establish how the Sun’ temperature, density, and composition vary with distance from the centre. Oscillations in the photosphere are also used to study the movement of the interior of the Sun. About ten million separate sounds, each traveling in a different, defined section of the solar interior, combine to produce the oscillations in the photosphere. By separating the different vibrations and tracing them back to their origins it is possible to look into the heart of the Sun.

The Sun produces an amazing amount of light and heat. In just one second the Sun emits more energy than humans have used in the last ten thousand years. A bushfire the size of the Sun would consume the mass of the Sun in a few thousand years. The Sun uses nuclear fusion reactions which release energy and tiny elementary particles, permitting the Sun to shine relatively steadily for 4.6 billion years.

All matter inside the Sun is gravitationally attracted to all the other matter in the Sun, and this attraction tends to pull the Sun’s mass together. This inward pull creates high pressures and temperatures inside the Sun. The centre is so violent and hot that collisions between atoms break the hydrogen atoms apart into their subatomic ingredients. A hydrogen atom is made up of a nucleus that contains a positively charged proton, and a negatively charged electron that orbits the nucleus. In the Sun, collisions separate the electron from the nucleus, freeing each to move about the solar interior. The positively charged nuclei, or protons, are called ions. A gas in which particles are ionized, or have electric charges, is called plasma. The energy that the Sun produces in its core must travel to the Sun’s surface to make the Sun glow. The mechanisms that transport radiation from the centre to the surface of the Sun define the structure and behaviour of the layers inside the Sun.

Like Earth, the Sun rotates, or spins, around an imaginary line that runs through its centre. This line is called the Sun's axis, and the top and bottom of this line mark the Sun's north and south poles, in the same way that Earth's axis marks the North Pole and South Pole on Earth.

Earth, the Sun, and the other planets in the solar system all lie on one plane, and the Sun's north pole and Earth¹s North Pole are oriented in roughly the same direction relative to the plane. The Sun's equator, like Earth's, is an imaginary line halfway between the north and south poles that runs east and west.

Like Earth, the Sun rotates from west to east when viewed from above the north pole, but unlike Earth, different parts of the Sun rotate at different rates. In the photosphere, the areas near the north and south poles of the Sun rotate more slowly than the areas nearer the solar equator. A spot at the Sun’s equator takes 25 days to rotate completely, while a spot 15° from the poles takes 34 days to make a complete rotation. Sound waves moving in the direction opposite to the rotation of the Sun appear to move more slowly than those moving with the rotation of the Sun allowing helioseismologists to pinpoint the origins of fluctuations on the Sun’s surface and compare sound waves that have taken different paths to the surface. Armed with this sensitive indicator, it has been possible to show that the differential rotation of the photosphere persists throughout the convective zone but disappear in the underlying radiative zone, where the rotation speed becomes uniform from pole to pole. At the boundary between the convective and radiative zones, the different rotation speeds cause the material in the zones to rub together. The forces generated by the two zones moving against each other are thought to create the Sun’s magnetic field.

The separation of hydrogen nuclei from their electrons makes nuclear fusion possible at the Sun's core, producing the Sun's light and heat. With their electrons gone, the proton in each hydrogen nuclei can be packed much more tightly than complete atoms. At great depths inside the Sun, the pressure of the overlying material is enormous, the protons are squeezed tightly together, and the material is very hot and densely concentrated. At the Sun's centre, the temperature is 28 million degrees Fahrenheit and the density is more than 13 times that of solid lead; hot and dense enough to make the nuclei fuse together.

The nuclear fusion reaction that powers the Sun involves four protons that fuse together to make one nucleus of helium. Two of the original protons become electrically neutral particles about the same size as protons known as ‘neutrons’, resulting in is a helium nucleus containing two protons and two neutrons. The helium nucleus is 0.7 percent less massive than the four protons that combine to make it and so the missing mass of the fusion reaction is turned into the energy, which powers the Sun. The relationship between energy and the missing matter was explained in 1905 by Albert Einstein. The mass loss, m, during the transformation of four protons into one helium nucleus, supplies an energy, E, according to the relation E = mc2, where c is the speed of light. The speed of light is a constant number equal to 1 ¥ 109 feet per second. The result is that every second, fusion reactions convert about 700 million metric tons of hydrogen into helium within the Sun¹s energy-generating core. In doing so, about 5 million metric tons of matter become energy, leaving the Sun as radiation. The part of this radiation that constitutes visible light is what makes the Sun shine.

The rate of nuclear reactions in the Sun is relatively low, because protons repel each other and must overcome this repulsion in order to fuse together. Only a tiny fraction of the protons inside the Sun are moving fast enough to overpower this repulsive electrical force. When the nuclei that are moving fast enough to get very close together, the strong nuclear force, which is very powerful over very short distances, takes over and pulls the nuclei together and holds them. In this way, nuclear reactions proceed at a relatively slow pace inside the Sun. If the pace were much quicker, the Sun would explode like a giant hydrogen bomb.

The conversion of two protons into two neutrons in the proton-proton chain produces two tiny, elusive, fast-moving neutral particles called neutrinos. Nuclear reactions in the Sun's central furnace create prodigious quantities of neutrinos. Every second the Sun releases 2 ¥ 1038 neutrinos, and every second an estimated 70 billion of these solar neutrinos pass through every square centimeter of Earth that is facing the Sun. Neutrinos move at the velocity of light, have no electrical charge, and have so little mass that scientists are not sure they have any at all. The ghostlike neutrinos therefore travel almost unimpeded through the Sun, Earth, and nearly any amount of matter. Scientists can snag small numbers of neutrinos in massive underground detectors called neutrino telescopes. These telescopes are placed so deep underground that only neutrinos can reach them. Scientists using these telescopes have detected solar neutrinos, confirming that the Sun is indeed powered by nuclear fusion. Unfortunately the number of neutrinos detected by these telescopes is only one-third to one-half of the total number of neutrinos predicted theoretically. This discrepancy between the number of detected neutrinos and the number predicted is the Solar Neutrino Problem. There are two possible explanations: scientists might not understand exactly how the Sun produces its energy, or they have an incomplete knowledge of neutrinos.

Studies of the interior of the Sun substantiate the current models of how the Sun produces its energy, so the problem is assumed to be the understanding of neutrinos. The Sun produces at least three types of neutrinos: an electron neutrino and two other proven types of neutrinos are called muon neutrinos and tau neutrinos. Most neutrino telescopes, especially those devoted to solar research, can only detect electron neutrinos. In the 1990s studies of muon neutrinos, produced by reactions between cosmic rays and Earth’s atmosphere, showed that muon neutrinos might change into tau neutrinos suggesting that electron neutrinos from the Sun may also change into another type of neutrino. This would explain why the electron neutrino detectors miss many of the Sun’s neutrinos.

Nuclear fusion releases energy deep down inside the Sun’s high-temperature core, which extends from the centre to about one-quarter of the radius of the Sun. The layers above the core produce no energy. All the Sun’s energy, so the is produced by the core, which makes up 1.6 percent of the Sun's volume. Energy moves out from the core through two spherical shells surrounding the core. The inner shell is the radiative zone, and the outer shell is the convective zone, radiation and convection being the two ways energy travels from one place to another. Radiation involves the movement of energy, but not the movement of material. The radiative energy spreads out in all directions and can move between objects that are not connected. Radiation can be absorbed by another substance. With convection, matter moves energy and it occurs when a liquid or gas makes contact with an object at a different temperature.

Energy moves from the core of the Sun to the next innermost layer, the radiative zone, through radiation. The radiative zone spans from the outer edge of the core, which is 108,000 miles from the Sun’s centre, to 308,000 miles from the Sun’s centre. The radiation diffuses outward in a haphazard, zigzag pattern. Particles in the radiative zone repeatedly absorb, radiate, and deflect photons of energy. Matter in the radiative zone stays in the same place while the energy moves through it. Because of this continued ricocheting in the radiative zone it takes about 170,000 years for a photon of energy to work its way outward from the Sun’s core to the bottom of the convective zone.

The Sun's interior cools with increasing distance from the centre, as the heat and radiation of the core spread outward into an ever-larger volume. At the base of the convective zone, the temperature is about four million degrees Fahrenheit. At the boundary of the cooler convective zone, the radiative energy has lost too much intensity and the material is too cool and dense to allow the energy to pass through.

The layers of material at the bottom of the convective zone heat up with blocked radiation and become less dense than surrounding material. This heated material then moves up through the convective zone, carrying energy toward the Sun’s atmosphere. When the material reaches the atmosphere - a layer that is much less dense than the convective zone - the energy can radiate into space. The material at the top of the convective zone becomes cooler and denser when it releases its energy and falls back to the bottom to pick up more energy. The time a particle takes to pass through the convective zone, from the innermost to the outermost edge, is about ten days.

The behaviour of the outer, visible layer of the Sun provides a glimpse of the structure of the Sun’s interior. The visible part of the Sun is the photosphere, which heaves in and out with a rhythmic motion. The material in the photosphere can reach a height of 30 miles and speeds of 1,600 feet per second. The time for each oscillation to go from its highest point to its lowest and back again is its period. Each oscillation has a period of about five minutes.

The oscillations in the photosphere are actually caused by sound waves from the convective zone. Sound waves travel by compressing matter in their path. Because they rely on matter, sound waves cannot travel through a vacuum, or an area in which no matter is present. Air carries most of the sound on Earth. The hot plasma of the Sun carries sound waves within the Sun. Hot gas churns in the convective zone, producing a noise like a pot of boiling water, but much, much louder. When these sounds strike the photosphere and rebound back down, they disturb the gases there, causing them to rise and fall. The sound waves are trapped inside the Sun and cannot travel through the vacuum of space. Even if they could reach Earth, the Sun’s sounds are too low-pitched for the human ear to hear. A period of five minutes corresponds to 0.003 vibrations per second. The lowest sounds that even a sensitive human ear can hear have a frequency of about 25 vibrations per second.

Scientists can ‘listen’ to the Sun's vibrating notes indirectly by watching the rhythmic motions of the photosphere. Sensitive instruments detect the Sun’s oscillations by recording periodic changes in the wavelength of the Sun’s light. Motion at the solar photosphere changes the wavelength of the light that emitted. When oscillations on the Sun's photosphere move its material away from Earth, the Sun's light shifts to longer wavelengths. This shift occurs because each successive wave has farther to travel than the one before it did in order to reach Earth, so the distance between waves becomes longer. Photospheric oscillations that move material toward Earth make the wavelengths shorter. These changes in wavelength due to motion are called the Doppler Effect.

Data from the Solar and Heliospheric Observatory (SOHO)[1] spacecraft show clearly that powerful starquakes ripple around the sun in the wake of mighty solar flares that explode above its surface. The observations give solar physicists new insight into a long-running solar mystery, and may even provide a way of studying other stars. The outermost quarter of the sun’s interior is a layer of hot gas that is constantly churning. Turbulence in this region causes ripples that criss-cross the solar surface, making it heave up and down in a patchwork pattern of peaks and troughs. SOHO has proved to be an exceptional spacecraft for studying this phenomenon. Discovering how the ripples move around the sun has provided valuable information about the sun’s interior conditions. A class of vibrations, or oscillations, called the five-minute oscillations with a frequency of around three millihertz have proven particularly useful.

According to conventional thinking, the five-minute oscillations can be thought of as the sound you would get from a bell sitting in the middle of the desert and constantly being touched by random sand grains, blown on the wind. But what Christoffer Karoff and Hans Kjeldsen from the University of Aarhus saw in the data was very different. ‘The signal we saw was like someone occasionally walking up to the bell and striking it. This told us there was something missing from our understanding of how the sun works,’ Karoff says.

So they began looking for the culprit and discovered an unexpected correlation with solar flares. It seemed that when the number of solar flares went up, so did the strength of the five-minute oscillations. ‘The strength of the correlation was so strong that there can be no doubt about it,’ says Karoff. A similar phenomenon is known on Earth in the aftermath of large earthquakes. For example, after the 2004 Sumatra-Andaman earthquake, the whole Earth rang with seismic waves like a vibrating bell for several weeks. The correlation is not the end of the story. Now the researchers have to work to understand the mechanism by which the flares cause the oscillations. ‘We are not completely sure how the solar flares excite the global oscillations,’ says Karoff.

In a broader context, the correlation suggests that, by looking for similar oscillations within other stars, astronomers can monitor them for flares. Already Karoff has used high-technology instruments at major ground-based telescopes to look at other sun-like stars. In several cases he detected the tell-tale signs of oscillations that might originate from flares. ‘Now we need to monitor these stars for hundreds of days,’ he says. That will require dedicated spacecraft, such as the Convection, Rotation, and Planetary Transits (COROT) space telescope from the Centre National d’Etudes Spatiales mission at the European Space Agency. The hard work, it seems, is just starting.

 

The material in the Sun farther out from the center than the photosphere makes up the Sun's atmosphere. The atmosphere extends far beyond the disk we see in the sky. Very diffuse solar gases extend all the way to Earth and beyond. The solar atmosphere consists of, from the innermost part outward, the photosphere, the chromosphere, the corona, and the expanding outer layers of the corona that astronomers call the solar wind. The photosphere is the visible part of the Sun. We look right through the chromosphere, the corona, and the solar wind, just as we see through Earth’s atmosphere at night.

The chromosphere and corona are visible during total solar eclipses, when the Moon lines up between the Sun and Earth, completely blocking the main disk of the Sun from view. The thin chromosphere becomes visible a few seconds before or after a solar eclipse, creating a narrow pink, rose, or ruby-colored band at the edge of the Sun.

For up to eight minutes during an eclipse, the corona is visible to the unaided eye as a faint, shimmering halo of pearl-white light spreading out from the lunar silhouette. Although the light of the chromosphere and corona is not bright enough to be dangerous, and can be viewed safely without filters during the total phase of an eclipse, the partial phases of a solar eclipse are very hazardous to human eyes and can only be viewed indirectly or through special filters. Scientists can study all layers of the Sun’s atmosphere at any time using special instruments.

The photosphere is the lowest, densest level of the solar atmosphere. The visible light that reaches Earth from the Sun originates in the photosphere. That light comes from a thin, bright shell about 200 miles thick, a thickness of less than 0.05 percent of the Sun¹s radius. The photosphere has a temperature of 9950°F. It is a diffuse, tenuous gas with a pressure that is only a small fraction, 0.0001, of the amount of pressure in Earth’s atmosphere at sea level. The photosphere is opaque, because it contains negative hydrogen ions. Hydrogen ions block, absorb, and emit light, all of which prevent light from passing directly through a cloud of hydrogen ions.

Some images of the Sun suggest that its white-hot disk is perfectly round and smooth, without a blemish. This uniform appearance is misleading. Under close inspection, the photosphere breaks into a million tiny bright points, called granules, with a strongly textured and varying pattern. The hot granules are about 900 miles across, and they are grouped into much larger supergranules about 20,000 miles in diameter.

Granules are places within the photosphere where hot, bright material reaches the surface. The granules are in constant turmoil and change. Hot gas rises up, liberating its energy. After the gas cools, it sinks downward along the dark lanes between the granules. Each bright cell lasts only a few minutes before it is replaced by another. This honeycomb of rising and falling gas marks the top of the convective zone.

Large, dark spots, called sunspots, are often visible in the photosphere. The biggest sunspots exceed Earth in size and are easily visible with a telescope. Sunspots rotate with the Sun and change in size and shape. They come and go, with lifetimes lasting from hours to months. The number of sunspots increases, then decreases, over an 11-year cycle. The position of sunspots changes as the number changes. Sunspots are concentrated in two belts, one north and one south of the solar equator. When the number of sunspots is at a minimum, the belts are near the equator. When the number of sunspots is at its maximum, the belts are at higher latitudes, nearer the poles.

Sunspots are places in the Sun’s photosphere that contain magnetic fields thousands of times stronger than Earth's magnetic field. Sunspots appear dark, because they are much cooler than their bright surroundings. The concentrated magnetism in sunspots keeps them cold. The strong magnetic field of a sunspot acts as a valve, choking off the heat, light, and energy flowing outward from the solar interior. This valve-like action keeps sunspots at a temperature of 5850°F or just over half the temperature of the surrounding photospheric gas.

While sunspots are darker than their surroundings, they still radiate light. A sunspot is about ten times brighter than the full Moon. Scientists were perplexed for decades over what holds sunspots together, believing that the outward pressure of the strong, localized magnetic fields concentrated in sunspots should make the sunspots expand and disperse. By examining motions beneath sunspots, helioseismologists have shown that flows of gas converge below sunspots. The converging flows force the surface magnetic fields together and concentrate them to form sunspots.

Sunlight appears yellowish, but it is actually a combination of a rainbow of colors. Dark absorption lines in the spectra of the Sun and other stars fingerprint the ingredients of these stars as each chemical element produces a unique set of lines, and the presence of these lines shows that a particular element is present in the stellar photosphere. Darker absorption lines indicate greater absorption and therefore larger amounts of the element. Absorption lines in the Sun’s spectrum show that hydrogen is by far the most abundant element in the Sun. Other prominent absorption lines are produced by helium, sodium, calcium, and iron. Altogether, 92.1 percent of the atoms in the Sun are hydrogen atoms, 7.8 percent are helium atoms, and the other, heavier elements - sodium, calcium, iron, and other elements - make up only 0.1 percent of the atoms in the Sun.

The chromosphere is a thin layer about 1 200 to 1 900 miles thick, just above the visible photosphere. The chromosphere’s temperature rises from 9950°F near the photosphere to about 17,500°F near the corona. At these temperatures hydrogen emits a distinctive deep red color. The chromosphere is often studied by filtering out all sunlight except the light that has the wavelength produced by hydrogen. Calcium atoms with one electron missing also produce distinctive radiation in the chromosphere. These calcium ions emit ultraviolet light which is also useful for examining details in the chromosphere.

Hydrogen and calcium emissions reveal huge regions of cool, dense gas suspended above the photosphere by powerful magnetic fields. The cool gas looks dark against the brightness of the Sun beneath it. At the edge of the disk of the Sun, where the chromosphere extends beyond the lower layers of the Sun, the gas of the chromosphere creates bright loops or ‘prominences’ against the dark sky. Against the surface of the Sun, however, these prominences look dark. Prominences are often called filaments when they appear against the background of the hot Sun. Sunspots extend from the photosphere into the chromosphere, creating even darker spots on the chromosphere. Hot gas from the photosphere penetrates the chromosphere around the sunspots, creating bright regions or ‘plages’.

The corona is the very hot layer of the solar atmosphere above the chromosphere. It extends to Earth and beyond as the solar wind. The Sun’s temperature rises to 4 million degrees F at the bottom of the corona, and remains almost that hot as it reaches Earth. The high temperature of the corona presents one of the most puzzling problems of solar physics. The chromosphere and photosphere are closer to the Sun’s core than the corona, but the corona is several hundred times hotter. As heat cannot normally move from a cooler area to a warmer area, this suggests the high temperature of the corona is due to the Sun’s magnetic fields instead of radiation from the Sun’s core.

Comparisons of the corona and the Sun's magnetic fields have shown that the corona is hottest where the magnetic fields are strongest. The entire corona is stitched together by thin, bright, magnetized loops of material that constrain the hot, dense gas of the corona and shine brightly at X-ray wavelengths. These loops are in a continuous state of change - they can rise from inside the Sun, sink back down into it, or expand into space. They often come together, sometimes merging with each other and sometimes destroying each other. The magnetic loops store magnetic energy. When they interact, the magnetic loops release their stored energy into the corona, providing the energy that keeps the corona so hot. The corona’s magnetic field also has gaps in it, called coronal holes. Coronal holes appear through the telescope as large dark areas that are cooler and contain less material than the rest of the corona.

Spectral lines come from atoms emitting and absorbing light when their electrons gain or lose energy. The corona is so hot that atoms in the corona are stripped of some of their electrons. These atoms then have different numbers and arrangements of electrons from atoms in the rest of the atmosphere and thus produce different spectral lines. The corona emits most of its radiation at very short ultraviolet and X-ray wavelengths. The underlying photosphere emits very little radiation in these parts of the spectrum, so an image of the Sun in short ultraviolet and X-ray wavelengths produces an accurate picture of the corona. Much of the ultraviolet and X-ray radiation that hits Earth’s atmosphere is absorbed by atoms and molecules in the atmosphere, so study of the corona is done from spacecrafts.

Studies of the corona reveal dramatic, violent events called solar flares and coronal mass ejections (CMEs). Solar flares release energy from magnetic loops in the corona, heating the gases of the corona and sending particles and radiation out into the solar system. A coronal mass ejection occurs when an explosion in the corona pushes millions or billions of metric tons of material out into space. The frequency of occurrence of both solar flares and CMEs follows the pattern of the 11-year sunspot cycle. As the number of sunspots increases, so do solar flares and CMEs. Both kinds of solar explosions seem to result from the sudden release of energy stored in coronal magnetic fields.

The Sun’s ever-changing magnetism produces unrest on an awesome scale. The sudden, brief, intense outbursts of solar flares can rip through the Sun’s atmosphere with tremendous violence. They release energy equivalent to that of billions of hydrogen bombs in a just few minutes, increasing the temperature of Earth-sized regions of the corona by ten times and flooding the solar system with intense radiation. During a solar flare, the tops of magnetized coronal loops release energy. In less than a second, electrons and positive ions within these loops accelerate to nearly the speed of light. The explosion hurls the electrons and ions out into space and down into the Sun. The particles strike the dense chromosphere below and produce high-energy X-rays and gamma rays.

Solar flares are probably triggered when oppositely directed magnetic fields come together in the corona, releasing their stored magnetic energy in a manner similar to that of a tightly twisted rubber band that suddenly snaps. After releasing their pent-up energy, the magnetic fields reconnect and relax to a stable configuration.

Coronal mass ejections are giant magnetic bubbles that expand to nearly the size of the Sun itself as they leave the low corona. The CMEs move outward at speeds from 100 to 600 miles per second. They carry up to 10 billion metric tons of coronal material into the space of the solar system. They accelerate and propel ahead of them vast quantities of high-speed particles. CMEs sometimes occur when part of the coronal magnetic field becomes sheared and twisted, often disrupting a loop of material in the chromosphere. This prominence or filament shoots through the chromosphere into the corona, carrying material with it.

Earth is affected by the radiation and particles that solar flares and coronal mass ejections release. Intense radiation from a solar flare reaches Earth's atmosphere in just eight minutes. The X-ray radiation of these solar flares strips electrons from atoms and molecules in Earth's atmosphere, changing the electrical properties of the atmosphere. This change can disrupt radio communications and make the atmosphere expand farther into space than usual. Friction can develop between the expanded atmosphere and satellites that orbit near Earth, slowing down the satellites.

Frequent solar flares can also increase levels of ultraviolet radiation in the atmosphere, which in turn changes oxygen into ozone with three oxygen atoms instead of the usual two. This added ozone actually helps block harmful radiation from the Sun. Particles that solar flares and CMEs release take a day or more to reach Earth. Blasts of these particles can compress Earth’s magnetic field. Disruptions in the Earth’s magnetic field can cause it to compress before relaxing back to its normal intensity. The increased intensity of the magnetic field can interfere with signals passing through the atmosphere and cause power surges on electricity grids. CMEs also trigger intense auroras near the Earth’s poles when energetic particles enter the atmosphere.

Solar flares and CMEs have such a large potential for affecting Earth that space weather is continuously monitored from Earth and from space. Solar flares and CMEs are tied to the cycle of solar activity. The most recent maximum of solar activity occurred in 2001, and the next should occur in 2012.

The outermost part of the Sun is a stream of particles that flows from the Sun into the solar system. This ‘solar wind’ is the corona expanding into space and extends all the way to the heliopause, far past the orbit of Pluto. The corona is so hot that it cannot stand still. It is expanding outward in all directions, filling the solar system with a ceaseless flow of electrons, ions, and magnetic fields. The solar wind has two components. The fast part of the wind pours out of the regions near the poles of the Sun at speeds around 470 miles per second. The slower component gusts unevenly from the Sun's equatorial regions at speeds between 190 and 250 miles per second.

It is believed that the fastest part of the solar wind leaves the Sun through cool spots in the corona known as coronal holes. The magnetic field of the Sun is relatively weak around coronal holes and thus allows particles in the solar wind to escape. Heavier particles move more quickly than lighter particles in the same stream within coronal holes. The intermittent gusts from nearer the equator come from solar flares and coronal mass ejections. Both components of the solar wind gain speed as they spread out and leave the Sun. The fast component reaches its top speed close to the Sun, but the slow solar wind continues gaining speed much farther out.

The Sun rotates as it emits the solar wind, so the solar wind spirals around the solar system. The solar wind carrying the Sun’s magnetic field sets up a spiral magnetic field throughout the solar system. The solar wind and its magnetic field affect the magnetic fields of the planets, the direction of the tails of comets, and the flight paths of spacecraft.

The Sun is so important to life on Earth that humans have always paid special attention to it. The movement of the Sun across the sky helps mark time. The change throughout the year in the Sun's daily path helps mark the seasons. The shape traced out by the Sun over the course of a year is called an analemma.

Many cultures attach special significance to solar events, such as eclipses. The brightness of the Sun made studying it closely difficult for humans for many years. Looking at the Sun directly is dangerous, and even thick clouds do little to protect human eyes from the damage that direct sunlight causes. Astronomers could not make true scientific studies of the Sun until they developed techniques to observe the Sun indirectly.

The study of the Sun has both pushed and been pushed by revolutionary scientific discoveries. Early indirect observations of the Sun, using a telescope, allowed scientific study of the Sun to begin, showing that the Sun is a dynamic, changing body. The development of spectroscopy and the discovery of elementary particles and nuclear fusion allowed scientists to begin to understand the composition of the Sun and the processes that fuel it. The development of artificial satellites and other spacecraft finally allowed scientists to study the Sun from space, allowing a full view of all of the Sun's radiation and a continuous study of the Sun.

Greek philosopher Aristotle was the first known person to use a device that allowed indirect observation of the Sun. Sometime between 384 BC and 322 BC Aristotle noticed that a hole in a screen would create an image of the Sun on the ground, if the screen were between the Sun and the ground. He made a simple version of a device called a camera obscura to take advantage of this effect. A camera obscura is still a popular way to observe solar eclipses.

Italian scientist Galileo observed the Sun with a telescope for the first time in 1610. Looking through a telescope directly at the Sun is even more dangerous than looking at the Sun with the naked eye, so Galileo turned the telescope into a camera obscura. He pointed it at the Sun and then set up a screen behind the eyepiece. The eyepiece projected the image of the Sun onto the screen. Galileo observed sunspots with his telescope. He saw that sunspots rotate with the Sun and change in size and shape. Galileo's work showed that the Sun is a changing and active body.

The next major breakthrough in the study of the Sun was the development of ways to study sunlight. In the mid-17th century English scientist Isaac Newton used a prism - a specially cut chunk of glass - to break sunlight down into its different colors. This range of colors is called the Sun¹s spectrum, and the study of spectra is called spectroscopy.

In 1802 British scientist William Wollaston found that the solar spectrum was cut by several dark gaps. By 1815 German physicist Joseph von Fraunhofer had cataloged the wavelengths of more than 300 of these ‘absorption lines’ and assigned letters to the most prominent of them. In the mid-19th century German scientists Gustav Kirchhoff and Robert Bunsen related the absorption lines in the Sun’s spectrum to chemical elements. In 1925 English-born American astronomer Cecilia Payne (later Cecilia Payne-Gaposchkin) compared the spectrum of the Sun to that of other stars to show that virtually all bright, middle-aged stars have the same composition.

The spectrum of the Sun's corona was studied for the first time in the mid-19th century. During the solar eclipse of August 7, 1869, American astronomers Charles A. Young and William Harkness independently discovered that the corona¹s spectrum featured an especially bright line of green light. Bright lines in a spectrum are called emission lines. They are the fingerprints of elements in the substance producing the light. The corona's bright green emission line comes from highly ionized iron, indicating that the corona has very high temperatures.

Detailed studies of the Sun's photosphere and the sunspots began with Galileo's telescopic camera obscura in the 17th century. The next revolution in this area occurred in the 1840s, when German scientist Heinrich Schwabe discovered that the number and positions of sunspots vary over an 11-year period. In 1859 British astronomer Richard Carrington discovered solar flares, as discovery which helped explain that geomagnetic storms (increased intensity of Earth’s magnetic field) are related to events on the Sun. In 1908 American astronomer George Ellery Hale showed that sunspots contain magnetic fields that are thousands of times stronger than Earth’s magnetic field.

The Sun produces an enormous amount of energy. Scientists could not explain how something with the mass of the Sun could produce so much energy until they discovered nuclear fusion. The details of just how nuclear fusion changes hydrogen into helium nuclei were not known until discoveries in the field of elementary particles were made. The most familiar particles - those that make up atoms - are protons, neutrons, and electrons. Protons and neutrons are the main particles involved in nuclear fusion. Both types of particles are about the same size and mass, but protons have a positive electric charge, while neutrons are electrically neutral. New Zealand-born British physicist Ernest Rutherford discovered the proton in 1918. British physicist Sir James Chadwick discovered the neutron in 1932, and was awarded the 1935 Nobel Prize in physics for his discovery.

The first fusion reaction in a laboratory occurred in the early 1930s. In 1938 German-born American physicist Hans A. Bethe and American physicist Charles L. Critchfield demonstrated how a sequence of nuclear reactions, called the proton-proton chain, makes the Sun shine. Bethe was awarded the 1967 Nobel Prize in physics for his discoveries concerning energy production in stars.

After scientists understood how the Sun produces its energy, they began developing theories to explain how the Sun’s energy travels from the core to the Sun’s atmosphere. For the first few decades after the discovery that fusion powers the Sun, scientists deduced the Sun’s structure by comparing the theoretical output of the Sun’s core to the energy actually released at the Sun’s atmosphere.

In the 1960s American physicist Robert Leighton developed a camera that could record Doppler shifts in light at the Sun’s surface. A Doppler shift is a change in the wavelength of light caused by the movement of the object that is emitting the light. If the object is moving away from the observer, each wave will have to travel farther to reach the observer, making the distance between waves (the wavelength) longer. An object moving toward the observer will seem to emit light with a shorter wavelength. Leighton discovered that the Sun seemed to pulsate in and out, making a complete cycle about every five minutes. Leighton's discovery launched the field of helioseismology, or the study of the Sun's interior by observing the vibrations of the Sun and how sound waves move through it.

In the 1970s scientists demonstrated that the entire Sun is vibrating with organized rhythms extending to its core and developed models of the interior of the Sun based on vibrations at its surface. In 1995 six observatories around the world coordinated with each other to begin observing the oscillations of the Sun as a team. This project, a collaboration of 20 nations, is called the Global Oscillation Network Group (GONG). GONG can keep constant watch on the Sun because, at any given time, daytime is being experienced by at least one of the observatories.

Studying the Sun from space has revolutionized solar physics. Since the first observations from space began to be made, there have been great advances in the study of the Sun's surface, energy production, structure, and relationship to Earth and the solar system. Study from space began in 1957 when the Soviet satellite Sputnik 2, the second satellite to go into space, carried instruments to study the Sun.

The series of missions by the Pioneer spacecraft of the United States included several experiments to study the Sun and its relationship to Earth. The Pioneer program lasted from the late 1950s to the 1970s. The US Mariner 2 spacecraft, launched in 1962, used data obtained from its voyage to Venus to demonstrate that a low-speed solar wind is continuously emitted from the Sun, and also discovered high-speed streams in the Sun's winds.

In the 1960s and 1970s the US Orbiting Solar Observatory (OSO) series studied the Sun over an entire cycle of solar activity. One of the satellites in the OSO series was the piloted Skylab Space Station, launched in 1973. Skylab astronauts used X-ray telescopes to transform our knowledge of the Sun¹s corona. In the early 1980s the United States launched the Solar Maximum Mission spacecraft to study the Sun during its most active period. The joint Japanese, US, and British probe Yohkoh studied solar flares through the 1990s.

Two of the most productive solar spacecraft of the late 1990s and early 2000s were the Ulysses spacecraft and the Solar and Heliospheric Observatory (SOHO). Both spacecraft are joint projects of NASA and the European Space Agency (ESA).

Ulysses was launched in 1990 and SOHO was launched in 1995. Ulysses' orbit takes it over the poles of the Sun, then back to the planet Jupiter to get a gravitational boost that sends the spacecraft back to the Sun. By 2001 Ulysses had passed over the Sun’s north and south poles twice. Ulysses' mission has contributed much knowledge about the solar wind in regions above the Sun's poles. Findings from this mission conclusively demonstrated that the fast component of the solar wind pours out at high solar latitudes, including from polar coronal holes. The slow component of the solar wind is constrained to low latitudes near the solar equator. Ulysses also found that the Sun's magnetic field does not warp at the poles as much as expected.

SOHO is at a point in space where the Sun's gravitational pull balances Earth's gravitational pull, so the satellite orbits the Sun with Earth. SOHO always faces the Sun. This probe has allowed scientists to make great leaps forward in their understanding of the structure and dynamics of the solar interior, the heating mechanisms of the solar corona, and the origin and acceleration of the solar wind. SOHO has returned amazing images of the Sun, including comets hitting the Sun and features on the Sun’s surface that scientists compare to tidal waves, tornadoes, and rivers.

The Sun and planets in our solar system formed when a rotating cloud of dust and gas in space collapsed, or condensed, due to the gravitational attraction between the particles in the cloud. A nearby supernova explosion may have triggered the collapse, or a random fluctuation in the density of the cloud may have started the process. The Sun formed at the center of the spinning cloud, while the debris that condensed into planets formed a flattened disk revolving around the Sun. When the Sun reached its present size about 4.6 billion years ago, it was hot enough inside to ignite the nuclear reactions that make it glow.

The Sun cannot shine forever, because it will eventually use up its present fuel. The nuclear fusion reactions that make the Sun glow (for more information, see the section entitled The Sun¹s Energy in this article) depend on the element hydrogen, but the hydrogen in the Sun's core will eventually run out. Nuclear reactions have converted about 37 percent of the hydrogen originally in the Sun's core into helium. Astronomers estimate that the Sun¹s core will run out of hydrogen in about 7 billion years.

The Sun will grow steadily brighter as time goes on and more helium accumulates in its core. Even as the supply of hydrogen dwindles, the Sun's core must keep producing enough pressure to keep the Sun from collapsing in on itself. The only way it can do this is to increase its temperature.

The increase in temperature raises the rate at which nuclear reactions occur and makes the Sun brighter. In 3 billion years, the Sun will be hot enough to boil Earth¹s oceans away. Four billion years thereafter, the Sun will have used up all its hydrogen and will balloon into a giant star that engulfs the planet Mercury. At this point in its life, the Sun will be a red giant star. The Sun will then be 2,000 times brighter than it is now, and hot enough to melt Earth¹s rocks. At this time the outer solar system will get warmer and more habitable. The icy moons of the giant planets may warm enough to be covered by water instead of ice.

When the giant Sun uses up its fuel, it will no longer be able to support the weight of its inner layers, and they will begin to collapse toward the core, eventually producing a small, dense, cool star called a white dwarf. The Sun will then have about the same radius as Earth has, but it will be much denser and more massive than Earth. The Sun will become a white dwarf star about 8 billion years from now. After it becomes a white dwarf, it will cool slowly for billions of years, eventually becoming so cool that it will no longer emit light.

Solar maximum is the period of greatest solar activity in the solar cycle of the sun. During solar maximum, sunspots appear. Solar maximum is contrasted with solar minimum. Solar maximum is the period when the suns magnetic field lines are the most distorted due to the magnetic field on the solar equator rotating at a slightly faster pace than at the solar poles. The sun takes about 11 years to go from one solar maximum to another and 22 years to complete a full cycle (where the magnetic charge on the poles is the same). The last solar maximum was in 2001, and on March 10, 2006 NASA researchers announced that the next cycle would be the strongest since the historic maximum in 1958 in which northern lights could be seen as far south as Mexico. This projection was based on research done by Mausumi Dikpati of the National Center for Atmospheric Research (NCAR).

 

In the 1920s behavioural science was gaining ground and with it credibility, primarily through theories of mind put forward by the early psychologists Freud, Reich and Jung. It was in this climate that others discussed the nature-nurture debate. Was personality determined by nature (parentage) or nurture, the environment within which childhood and adolescence takes place?

In Germany psychologist Johan Lange reasoned that if behaviour were inherited then this would show in studies of the behaviour of one-egg identical twins. These could be expected to develop and behave in the same way because they carried the same genes. Conversely the behaviour of non-identical twins, those that developed from two separate female eggs containing different sets of genes would show no more than chance coincidence when compared.

Lange studied thirty pairs of adult twins, each separated at birth. Twelve of these pairs were of the one-egg variety and sixteen of the two-egg, with the remaining two doubtful. Of the sixteen pairs of non-identical twins, fifteen pairs showed that only one of each pair of twins had committed a crime. In ten of the twelve pairs, Lange found that the behaviour of the single-egg twins was due to heredity handed down from the parents.

Lange believed his experiment showed that behaviour relates to heredity. But study of Lange’s data actually suggests otherwise when the criminal behaviour of siblings and parents are taken into account. The full data set shows that behaviour is genetic but this was not the whole story. Something was influencing the genes after they had been released by the parents.

Non-chemical agents of genetic mutation are x-rays, gamma rays, microwaves, magnetic and electro-magnetic energy. Astrologers maintain that twelve types of personality exist associated with the twelve signs of the zodiac. If twelve types exist, then somewhere there will be twelve types of mutation and there must be some mechanism that acts on the developing foetus to produce this effect. The sun provides such a mechanism.

to be continued

May 2009

based on
Appendix I
of
The Tutankhamun Prophecies
by
Maurice Cotterell

(Headline, London, 1999, ISBN 0 7472 6050 8)

May 2009

based on
Appendix I
of
The Tutankhamun Prophecies
by
Maurice Cotterell

(Headline, London, 1999, ISBN 0 7472 6050 8)

May 2009

based on
Appendix I
of
The Tutankhamun Prophecies
by
Maurice Cotterell

(Headline, London, 1999, ISBN 0 7472 6050 8)