Our Sun
This is a brief look at our star, the Sun, its creation, its structure, function, and some of the internal and surface characteristics of our star, as well as recent developments in solar observations, and a few of my own personal experiments as they related to the Sun.
Content
Our Sun
By Rex A. Crouch
© 2005
16 April 20 05
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Abstract This is a brief look at our Sun, its creation, its structure, function, and some of the internal and surface characteristics of our star as well as recent developments in solar observations, and a few of my own personal experiments as they related to the Sun.
Introduction. Just less than 5 billion years ago, in a spiraling arm of our Milky Way galaxy, a cloud of gas, and dust began to compressing under its own weight. The particles within the cloud's core became so densely packed that they frequently collided, and fused together. The fusion process released tremendous amounts of heat, and light which could then compete with the force of gravity within the cloud. The two forces eventually found an equilibrium point, and a star was born. This star in question is our Sun. All stars in our galaxy and other galaxies come in various sizes and colors. All stars are relatively unique. Our sun is a medium sized star known as a yellow dwarf, or a G Class star on the Hertzsprung-Russel Diagram. Our Sun, located just 149,598,000 km from Earth has a radius of 696,000 km, a mass of 1.9891 X 1030 kg , and a surface temperature of about 5800 Kelvin. Our Sun is composed of (by mass), 74% hydrogen, 25% helium, and 1% all other elements. Because hydrogen has very little mass, the composition of the Sun by number of atoms would be 92% hydrogen, 7.8% helium, and 0.1% all other elements. The cloud from which our Sun formed did not use all of its gases and dust to make the Sun. The leftover gases and dust were used to form the planets of our solar system (Harvard Science Department, 2002). Our Sun has been fusing hydrogen into helium and providing Earth with radiant energy for about 4.5 billion years, and we expected it to continue doing so for another
4.5 billion years. Of course one day our Sun will expend it hydrogen to the point that it can no longer fight the force of gravity of its developing iron core. Gravity will then begin to compress the Sun under its own weight; yet again but the fusion process is changing as the Sun matures. The compression causes the new helium particles inside of the core to collide hard enough that they can stick together and fuse. The core then begins to fuse helium into carbon to create enough energy to maintain its balance with the force of gravity it is quickly growing iron core. Creating carbon gives off more energy than did the making of helium. The energy being pumped out of the core radiates through the outer layers of the sun. The introduction of too much energy into the sun’s envelope heats up the envelope particles to the point that the envelope expands. The Sun's envelope will expand and engulf all of the inner solar system out to the radius of Mars. In the process the Sun will drop in temperature; this change in temperature will be marked by a change in color as the star becomes a red giant. Our sun will continue to live like this for maybe another billion years before pulsating and exploding into a planetary nebula probably leaving a white dwarf at the center. That is the life and death of our Sun in a nutshell. Sun’s Structure. The structure of the Sun is like looking at a fascinating piece of machinery except is has no tangible moving parts. In the below image developed by the SOHO Project Team, we begin with the
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Sun’s Core where nuclear fusion that produces the heat and light we experience here on Earth occurs. Next we find the Radiation Zone followed by the Convection Zone. The Photosphere, which is what we typically see in one of the lower layers of the Sun’s atmosphere is the next layer. We next find the Chromosphere which is a reddish orange layer thousands of kilometers thick. Lastly we find the Corona which is the upper most layer of atmosphere on the Sun; this layer extends millions of kilometers thick. Other aspects depicted in the below image are a prominence, and flare which will be discussed in more detail later.
referred to as direct (University of Tennessee Astrophysics Department, 2005). Fusion Process. As mentioned in the introduction, the Sun is composed of predominantly hydrogen, then helium, and a small percent of all other elements. The fusion process, as mentioned, occurs at the Sun’s core where the temperature is believed to be about 15 million °C and the pressure of gravity can alter the nuclear bonds of atoms. Because of the extreme heat and gravity on the Sun the fusion process is more complex than the process here on Earth in that the fusion process is a step-by-step process called a proton-proton chain. In this fusion process two atoms of hydrogen are combined to create what is called helium-4 and energy. This occurs in several steps: The pressure at the Sun’s core forces two hydrogen protons to combine to form a deuterium. Deuterium is one hydrogen atom with one neutron, one positron, and a single neutrino. Heat is beginning in this step. A proton and a deuterium atom combine to form a helium-3 atom. A helium-3 is the combination of two protons with one neutron, and a single photon of gamma ray. Lastly, two of these helium-3 atoms join under pressure to form a helium-4. This consists of two protons, two neutrons, and two protons. This three step process accounts for about 85 percent of the sun's energy. The remaining 15 percent comes from the following reactions: A helium-3 and a helium-4 combine to form a beryllium-7 which is not the most stable form of beryllium. This consists of four protons and three neutrons, and a gamma ray. A beryllium-7, because of its positive nature, captures an electron to become lithium-7. Lithium-7 consists of three protons and four neutrons, and one neutrino.
SOHO Project
Sun’s Rotation. ―The Sun is not actually a solid body.‖ Subsequently its rotational period is not well defined. To imagine a sphere of water suspended and spinning about on an axis system; water would tend to spin faster in some placed than in others. The modern measurements the Sun rotates once about every 25 days near its equator, 28 days at 40 degrees latitude, and 36 days near the poles. The rotation is the same as that of the planets which is sometimes
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The lithium-7 then combines with a proton to form two helium-4 atoms. The helium-4 atoms have less mass than the two hydrogen atoms that started the fusion process. Subsequently the difference in mass was converted to energy as Einstein elucidated in his theory of relativity, (E=mc2). The energy is emitted in various frequency lengths to include gamma, extreme ultraviolet, ultraviolet light, X-rays, visible light, infrared, microwaves and radio waves. If you were conducting the equations in your head with empirical formulas you may have noticed that some neutrinos and protons were not accounted for at the end of the equation. These unaccounted for particles that fell out of the equations are emitted from the Sun and create the solar winds which will also be addressed with more scrutiny. Before continuing I want to mention that the word ―burns‖ although inaccurate when talking about stars is nonetheless a commonly used word to refer to the fusion process in the Sun or a star. In addition to the last three steps, the Sun also burns other elements at various temperatures at other layers within the Sun as depicted in the below graph:
Heat – radiation Light – radiation Bandwidths Sun’s Magnetic Activities. Magnetism is the key to understand the Sun. Magnetic fields are the cause of all features we see on and above the Sun. The direction of moving charged particles is changed by magnetic forces. This forces increased orbital speeds of some electrons and slows others; this also induces electrons to jump to higher orbits within atoms. These changes in electron speeds changes the light emitted in terms of frequency. These changes in frequency allow us to remotely measure the Sun's magnetic field by observing the difference in the energy of the light emitted as these electrons jump from orbit to orbit. Both strength and direction of magnetic forces are measured on the Sun however we still do not fully understand the Sun’s magnetic forces (NASA Solar Physics Department, 2005). Initially a Dutch physicist named Pieter Zeeman observed in 1896 that a spectral line splits when the atoms are subject to very intensive magnetic fields. The more intense these magnetic field the more intense the spits in the spectral lines. Between Zeeman and the works of George Hale, it was shown that sunspots occur where magnetic fields concentrate. The importance of the magnetic field of the Sun was becoming clearer. Astronomers began taking pictures of the Sun at two wavelengths, one just greater than the other and between the two pictures they could construct what is called a magnetogram in which the magnetic fields of the solar atmosphere are displayed. In these manetograms the dark blue colors
Temperature ~2 x 108 °K ~5 x 108 °K
~10 x 108 °K
He burning occurs C burning occurs myriad reactions 12 C + 12C —> 24Mg + occur 3 4He —> 12C + 20 4 Ne —> 4He + 16O He + 12C —> 16O + 20 4 12 C + 12C —> 23Na + Ne + He —> 1 24 4 16 20 Mg + He + O —> Ne H 12 C + 12C —> 20Ne + 2 20Ne —> 16O + + 4 24 4 20 Mg + He + Ne —> He 24 24 Mg + 4He —> Mg + 28 Si + 44 Ca + 4He —> 48Ti +
NASA table
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represented area polarized north while the yellow colors represented magnetic lines polarized south. The sunspots did not seem to relate however the magnetic lines did. By the 1960s the astronomer Babcock presented the magnetic-dynamo model. In this model the magnetic fields wrap around the Sun, kink, and eventually unwrap. The study of Helioseismology, addressed further in this paper, added further explanations to the phenomena of magnetism in the Sun. Ultimately, astronomers learned that the magnetic field of the Sun expanded deeper into space than anyone of them initially thought. Of the Sun’s magnetic characteristics that affects us most is the Interplanetary Magnetic Field. The interplanetary magnetic field is a part of the Sun's magnetic field that is carried into solar system by the solar winds. The interplanetary magnetic field lines are sometimes referred to as "frozen in" to the solar wind plasma. As the Sun does rotate, the interplanetary magnetic field, much like the solar winds, travels outward in a spiral. The interplanetary magnetic fields originate in regions on the Sun where the magnetic fields appear to extend indefinitely into space; these regions are sometimes referred to as ―open‖ magnetic fields (Southwestern Research Institute, 2005). The below image from Southwestern Research Institute assist in depicting this spiral pattern of the interplanetary magnetic field.
Southwestern Research
Along the Sun's magnetic equator, the opposite open field lines run parallel to each other and are separated by a thin sheet of current called the "interplanetary current sheet". Because of an offset between the Sun’s rotational and magnetic fields, the current is tilted as depicted by the image below.
The IMF is a weak field, varying in strength near the Earth from 1 to 37 nT, with an average value of ~6 nT. This interplanetary current sheet and interplanetary magnetic field extend outward dissipating over distance. The end of the effects of the interplanetary magnetic field is found past Pluto where the outgoing solar wind and the incoming plasma from interstellar space meet, this is called the
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Heliopause, or the boundary of our solar system. The Sun’s magnetic activities lead us into the surface features on the Sun caused by magnetic activities. Features on the Sun’s Surface The below image from reveals plumes, flares, plagues, and strongly depicts the lines of magnetic flux that twist, and turn the flaming gases over the surface of the Sun (SOHO, 2001).
Galileo Project
SOHO
Sunspots and Plagues. Sunspots have been monitored extensively for a long period of time allowing us to determine cyclic behaviors. Galileo first began monitoring the sun with the use of a telescope in 1610. He made an observation each day for 35 days at about the same time of day documenting sunspots. This affords us our first view of the motion of sunspots across the surface of the Sun. The following image was drawn by Galileo (Galileo Project, 1995. Galileo’s improper solar observations later led to blindness.
These sunspots are actually disturbances in the magnetic fields in which magnetic lines protrude out of the Sun inducing sunspots. These sunspots are areas on the solar surface that appear dark because they are cooler than the surrounding photosphere. They are about 4500 K which is about 1500 K lower than the temperature of the rest of the photosphere. The darkness is only relative. Should you view just the sunspot against the darkness of space it would glow brightly. The darkest region in the center of the sunspot is called the umbra and the region around the umbra is named the penumbra. These sunspots tend to fluctuate in intensity over a period of 11.1 years. This 11.1 year cycle is known as Solar Maximum and Solar Minimum. The activity of the Sun increases drastically at Solar Maximum exhibiting more sunspot and other surface phenomena during any other time. The below images depict the vast differences between Maximum and Minimum.
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groups; and k is a variable scaling factor (typically <1) accounting for observing conditions and equipment from binoculars to space telescopes. Scientists combine data from lots of observatories -- each with its own k factor -- to arrive at a daily value. The second system is called the "International Sunspot Number," which is provided by the Sunspot Index Data Center in Belgium. The Boulder and the International numbers are calculated from the same basic formula except they use data different observatories; regardless, if you were to divide the International Sunspot Number or the Boulder Sunspot Number by 15, you will reach about the same number visible through a standard telescope. Sunspots tend to end in two fashions; they either fade away as the magnetic line retract back into the Sun or the magnetic lines breakdown resulting in an explosion called a solar flare. Plagues. Plague is French for "beach‖. Plagues are bright cloud-like features found around sunspots that represent areas of higher temperature and gas density within the Chromosphere of the Sun. Plagues are visible when photographed through filters passing the spectral light of calcium or hydrogen. These plagues are an extended emission feature of an active region that exists from the emergence of the initial magnetic flux inducing the sun spot until the widely scattered remnant magnetic fields merge with the background. These bright features are found near almost all active sunspot groups, and occur on a larger scale, and are brighter than facula.
The below image depicts a quickly growing sun spot in the lower left portion of the image while the four small dots in the upper right are the remnants of a previously massive sunspot
Space Weather Image
In this image we see two sunspot numbers. There are specific techniques used to calculate these sun spot numbers. Of the two sun spot numbering systems in use today, the foremost is the "Boulder Sunspot Number," which is computed by the NOAA Space Environment Center using a formula created by Mr. Rudolph Wolf in 1848. In his equation, R=k (10g+s), where R is the sunspot number; g is the number of sunspot groups on the solar disk; s is the total number of individual spots in all the sited
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The below image depicts a sunspot adjacent to a plage. In the image the plages is the represented as the whiter area near the top. It is fascinating to see that the plague disturbs the field lines otherwise uniformly surrounding the sunspot.
create, depending on their intensity; violent solar winds that effect power grids here on Earth, spacecrafts, and even the Earth’s magnetic shield and atmosphere. These solar flares are divided into four classes in which X-Class is the most sever and B-Class is essentially benign (Phillips, 2005) Type Measurement is Intensity (I) in Watts/ m2
X M
Class Flare Class Flare
I 10 10 10
5 6
4
I 10 I 10
6
4 5
C Class Flare
Big Bear Solar Observatory
B Class Flare
I 10
Solar Prominences. Solar Prominences are features found on, at, or near the surface of the Sun. The term prominence, strictly by definition refers to protrusions, projection, protuberance, or surface abnormalities. In the realms of astronomy some consider prominences to be solar surface events caused by magnetic activities in the Sun while others tend to refer to all surface activities as prominences. For the purpose this paper, I will refer to all protrusions, projections, and protuberances as prominences. These prominences are predominately caused by magnetism in one or more ways. Magnetic activities will be responsible for most of the remaining items discussed here. Of solar prominences I will address: Solar Flares Filaments Hyder Flares Polar Plumes
Solar Flares are sometime mistaken for Hyder Flares which will be addressed under Filaments. Filaments. Filaments consist of relatively cool, and dense gas suspended over the Sun’s surface in magnetic loops. These filaments collapse when their magnetic fields become unstable or otherwise collapse. The following two images show the before and after collapse of a solar filament viewed from the perpendicular:
Solar Flares. Solar Flares are massive eruptions of gases near the Sun’s surface sending energy into space through the entire electromagnetic spectrum. These flares can
Space Weather
A solar filament when viewed from a profile appears to be a large standing flame—they
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can appear to be very dramatic as they hover over the surface as depicted in the image below taken using ultraviolet cameras.
originating from bright points near the limb extend 30 to 60 arcseconds above the limb. The ramification or significance of these Polar Plumes has not been fully addressed as of current date. The following two images taken by SOHO were at the 1032 Å wavelength (white light).
SOHO Project
Hyder Flares. Hyder flares, named for Charles Hyder, occur when magnetic field lines protrude through the Sun’s surface under the filament and breakdown the magnetic lines creating the filament. These can be observed, much like most flares, in the Hydrogen-Alpha wavelength of 656.3 nm. These explosions typically occur away from the spotted regions. As these are rare, they are typically mistaken for solar flares and there are few images available. Polar Plumes. According to Harvard University, Polar Plumes are collimated flow tubes, specifically ―magnetically unipolar, linear, high density structures‖, that may carry the majority of the mass and energy of the solar winds that emanate from high-latitude regions of the Sun’s Corona. These Plumes occur in regions of simple magnetic topology in contrast to the rest of the Sun. Plumes were original observed using white light but are also visible using extreme ultraviolet. Observation of Polar Plumes using the SUMER instrumentation on SOHO have indicated through use of spectroheliograms with 1.5 arcsecond steps extending to about 8 arcminutes that these Polar Plumes, narrow jets or macrospicules
SOHO Project
The following image was taken at 195 Å wavelength (extreme ultraviolet) clearly depicting the plumes near the polar regions as tiny jets:
SOHO Project
Coronal Mass Ejections. According NASA Solar Physics Department, Coronal mass ejections are very large clouds of gas and plasma threaded by magnetic field lines to the surface of the Sun and subsequently ejected from the Sun over the course of a
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few hours. These Coronal Mass Ejections disrupt normal solar winds and cause solar winds of their own. These ejections release billions of ton’s of material into our planetary space at speed in excess of 500 km/s. According the University of Washington, there may be more than 10 billion tons of electrified and charged gases erupting from the Sun during each Coronal Mass Ejection. The below image from SOHO depicts an intense Corona Mass Ejection from the Sun’s southern pole region.
The mass ejections are often directly associated with the sunspots, which always lie in the Sun’s equatorial belt or at mid-latitudes. Other mass ejections occur near the Sun’s poles, far away from any sunspots. These events are most frequent at the peak of sunspot activity, but they can continue for a while as the count of sunspots begins to decline.‖ The SOHO Project has compiled data as depicted below that shows an increase in Corona Mass Ejections during Solar Maximum and in terms of an increase we also see that speed of the ejections is nearly 300 km/s faster during Maximum then Minimum however, the variations in width are essentially unchanged between Maximum and Minimum.
SOHO
These Corona Mass Ejections are not random but rather a method that the Sun uses to clean-up unwanted magnetic fields left by Sunspots and other abnormalities (Australian Institute of Geoscientists, 2005). The Sun is in fact housekeeping and sweeping out the dust to paraphrase the Geoscience web site. ―What emerges is a systematic pattern in the outbursts. It changes during the sunspot cycle, as the numbers of dark sunspots seen each day on the Sun’s bright surface first increases and then diminishes again.
Solar Winds. The solar wind streams off of the Sun radially in all directions at speeds of near 400 km/s. The source of the solar wind is the Sun's super hot corona. The temperature of the corona is so high that the Sun's gravity can no longer retain it. Although the solar wind is always directed away from the Sun it is not uniform. The speed changes and the wind carries with it magnetic clouds and there are interacting
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regions where high speed winds catches up with slow speed winds, and of course there are composition variations of all of these factors. The speed of the solar winds vary greatly from as high 800 km/s to as low as 300 km/s. The solar winds from the poles has been measured to a limited extent in which the Ulysses Mission launched from Discovery went as far as Jupiter, and used the gravity of the planet to double back and pass over the south pole of the Sun 1994, and the north pole in 1995. The orbital pattern places the spacecraft over the solar poles once every 6 years. The Ulysses Mission found that there is an abundance of He3 in the solar winds, and deuterium in the outer convection zone during polar studies of the Sun. Not unknown to us but nonetheless confirmed the Ulysses Mission was that solar flares and class III radio burst are related to solar winds and solar maximum. Study of Features Internal to the Sun Helioseismology. At the Wilcox Solar Observatory at Stanford University the subject of Helioseismology is the developing subject for them. This is the science of studying wave oscillation within the sun. As the sun is not a solid object there is no one source of seismic waves. In lieu of a titanic plate as found on Earth it is termed the source of agitation causing solar waves and in most cases the source of agitation is the convective region. As this is one region it is treated as a continuum. The oscillations have amplitudes of no more than about 0.1 meters per second. The goal at the Wilcox Observatory is to measure shifts of a spectrum line to an accuracy of parts per million of its width (Hoeksema, 2005). The types of waves the helioseismologist are looking for fall into three types – Acoustic Waves, Gravity Waves, and Surface Gravity Waves.
Acoustic Waves. Generating p-mode oscillations. The p-mode oscillations or pressure mode oscillations are forms of acoustic waves – Consider the fact that the Sun is ringing but not like a church bell being struck once but rather a bell be struck by millions of little particles over a continuous span. There is not one loud ring but a constant trill of rings. In terms of oscillations, we are not discussing flat two dimensional oscillations, nor even three dimensional oscillations like the ripples seen on-top of water but rather three dimensional spherical oscillations known as p-mode (pressure mode) shaped oscillations. The p modes can be described in terms of spherical harmonics. The spherical harmonics are characterized by three whole numbers: The order, given by n in physics is the number of nodes in the radial direction. The harmonic degree is known as l and indicates the number of node lines on the surface. This correlates directly to the total number of planes slicing through the Sun. The third number, m, tells how many of the surface nodal lines cross the equator and also gives the phase. The term m has boundaries of -l to +l as the direction of the waves are important in many cases. The term m, describes the number of planes slicing through the Sun longitudinally. The oscillations are nearly radial. The frequencies depend on the travel time of an acoustic wave across the star. The below image depicts p mode oscillations in the l direction.
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Stanford Image
The next image depicts p-mode oscillations in the l and m direction. The p mode with this spatial pattern causes motion of the surface that alternate in sign (in or out of the surface) in adjacent regions. The difference between m=+/-18 is the phase (in or out) of the pattern. Note that we have essentially broken the Sun up into Earth equivalent of latitude and longitude.
Stanford Image
Gravity Waves. Generating gmode oscillations. According to Newton, for every action there is an equal and opposite reaction. For the p-mode oscillations, the reaction is the g-mode oscillations. These are the gravity mode oscillations or the thought of as the restoring force or gravitational force perturbation. Gravity mode arises because gravity tends to smooth out material inhomogeneities along equipotential level-surfaces of the Sun. As the p-mode oscillations are non-uniform, they are a form of agitation as such is the gmode oscillations, subsequently these oscillations are referred to as perturbations. Surface Gravity Waves. Generating f mode oscillations. Everything wants to vibrate at a frequency that specific to its shape and composition. For stars, this oscillation is the fundamental oscillation, the
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f-mode oscillation. The nature frequency of vibration. The f-mode (fundamental) is a stable mode which exists only for non-radial oscillations. The frequency is proportional to the mean density of the star. The f-mode can also be derived with Newton’s uniform density of stars formula.
2
2l l 1 M 2l 1 R 3
Each oscillation mode is but one sampling of the Sun’s interior which acts like a resonant cavity. Of the p and f modes there are about 107 modes which does not include n harmonics. The study of p, g, and f mode oscillations is serving to make the Sun transparent allowing deeper study of sun which brings us to projects that SOHO has been developing in which the internal rotation of the Sun is now being map. Observations by the SOHO Satellite. In direct correlation with Helioseismology is the internal mapping of the Sun’s rotation by the SOHO project as Dr. Fleck of the SOHO project elucidated with me. While we have known for extensive period of time how the out surface of the Sun rotated is has not been until recent technology allowed us to make the Sun transparent and look at the inner rotations. One of the most significant observations has been the rotation of the convection zone. In the below SOHO image we see the stability of the convection zone as a uniform rotation but varies drastically as it spans out from 0 to 90 degrees.
Another means of looking at the rotations shows that there are correlations between frequency ranges and time (in terms of days) within the Sun.
Recent Developments. There have been a multitude of recent developments in solar observation. Helioseismology Holography. As mentioned there is the growing and developing science of Helioseismology. Synoptic Imaging of Active Regions on the far side of the Sun using Helioseismology Holography to monitor condensations of magnetic flux allowing astronomers to monitor sunspots on the far side of the Sun and providing more accurate space weather.
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Corona In-Flows. Still under study are newly discovered Corona In-Flows in which matter traveling between 20 km/s and 100 km/s is falling back into the Sun through the Corona. These In-Flow rates correlated with the occurrence of non-polar coronal holes and other indicators of nonaxisymmetric open flux per SOHO Project members. Personal Experiments. For the purpose of developing my research skills I have opted to conduct several of my own experiments. As stated, the purpose is to develop my own research skills, and practice analyzing and documenting my findings. I don’t anticipate finding anything new but the application will be a learning experience for me nonetheless. Measure lambda and voltage monitored over a 200 meter antenna of 9.5 oriented parallel to the ground, and East West in direction. Measurements were conducted at various times of the day and night to discern any difference as the angle of the sun varied throughout the day. This experiment failed miserably as there was no way of discerning exactly where these long wave frequencies were originating or even isolating one frequency range to monitor. This experiment should be conducted again, except care should be taken to ensure that the antenna is shielded from stray RF, and a band-pass filter should be employed to examining one particular segment of low frequency at a time. Measure diameter of sun using a high frequency receiver. In measuring the diameter of the Sun using a 10 GHZ to 12 GHZ receiver on a parabolic dish I learned nothing new about the diameter of the Sun, but the experiment itself was interesting. I measured the distance across the dish and then I aligned the parabolic receiver to the Sun’s path. Connecting the receiver to a
recording device and a monitor I was able to visually discern when a change in intensity began. A time measurement from this point, and I terminated the time measurement when the signal intensity dropped. The Sun traversed the 72 cm dish in 4 hours and 24 minutes. Bisecting the dish into two right angle triangles this turned the experiment into a trigonometry exercise with a visual confirmation on an LCD screen. The Sun is in fact 1,380,000 km. Photovoltaic cell measurements. Measure intensity of various frequencies by using photovoltaic cells receptive to specific frequencies. The photovoltaic cells produce a voltage representative to the amount of light received in that bandwidth. The 525 Nanometer (nm) wavelength corresponds to the green light produced by our Sun. 626 nm is red light produced, and received by us here on Earth. I also conducted measurements at two infrared wavelengths being 816 nm, and 940 nm, both obviously out of our visual spectrum. The data table also shows air mass which is a based on 1.00 representing the mass of air directly overhead as the baseline. Measuring the angle of the Sun to your position can give you the mass of air the Sunlight must travel through to reach your measurement location. I also sought to compare voltage outputs of photocells to protons per centimeter cubed I collected the following data on 27 March 2005 during clear skies, and stable high barometric pressure: 37° rising Sun 525 nm 626 nm 816 nm 940 nm .425 V .452 V .519 V .508 V
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48° rising
Sun 525 nm 626 nm 816 nm 940 nm
.564 V .604 V .617 V .618 V .337 V .304 V .332 V .335 V .220 V .237 V .275 V .274 V light frequency
43° setting
Sun 525 nm 626 nm 816 nm 940 nm
33° setting
Sun 525 nm 626 nm 816 nm 940 nm
Conclusion of measurements:
The lower the Sun angle which corresponds to thicker air mass, the lower the output intensity of all bandwidths. This was obvious without an experiment, but was fascinating to see first hand to what degree the impact of sun angle has radiation received by a position here on Earth. The intensity of shorter wavelengths was higher than those in the visible light spectrum. This is something that I previously did not know and sparked some additional research on my part. Monitoring protons per cubic centimeter through SOHO as I conducted these measurements on the four light frequencies, I found no correlations to voltage outputs of the four frequencies examined and proton output by the Sun. Summary. In summary, I provided an overview of the subject matter that comprises our Sun. From the Sun’s birth out of stellar gas and search for an equilibrium in gravity and burn to become a star to the eventual death of the life-force in
our solar system. The basic structure and inner workings were dissected to gain an insight to how our star creates energy— looking at the fusion process from the chemical level we saw that the Sun converts hydrogen into helium and how this accounted for 85% of the Sun’s energy while the remainder came from burns of other various elements derived from the fusions process. The Sun’s Magnetic activities were then addressed covering the Sun’s basic magnetic features to the Interplanetary Magnetic Field that carries the solar winds. A glimpse at the features on the Sun’s surface was provided in which we looked at sunspots and various solar prominences. Corona Mass Ejections, Solar Winds, and touched upon the internal fusion machine as we delved deeper to touch on the inner workings through Helioseismology to find the internal rotations of our star. In contacting researchers from various solar research facilities I found them to be very helpful and insightful as I queried their recent developments. Recent developments were fascinating and I for one am waiting anxiously to see the results of the new studies. Lastly I touched on some of my own personal experimentation conducted for personal development. I found that a 6000 word paper on the Sun was truly a difficult subject in that the limitation of words was at a threshold in which we are just above layman talk, but skimming the advance scientific dialog. This paper turned-out to be a document in transition in which I learned a great deal about our Sun, and developed an appreciation for how much more this is to know.
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References Albert Van Heldon ―Galileo Project,‖ 1995, http://galileo.rice.edu (February 10, 2005) Amara Graps, ―Helioseismology,‖ 2005, http://soi.stanford.edu/results/heliowhat.html (February 14, 2005) Australian Institute of Geoscientists ―Predicting Solar Outburst,‖ 2005, http://www.aig.asn.au/solar_outbursts.htm (March 25, 2005) Bernhard Fleck, PhD. ―Dr. SOHO,‖ 22 February 2005, personal email (22 February 2005) Craig C. Freudenrich, Ph.D. ―How Stuff Works,‖ How the Sun Works, 2005, http://science.howstuffworks.com/sun1.htm (February 9, 2005) (Einstein’s) general theory of relativity Harvard Science Department, ―The Sun,‖ April 11, 2002, http://hea-www.harvard.edu/scied/SUN/sunpage.html (February 22, 2005) NASA ―Jet Propulsion Laboratory,‖ 2005, http://genesismission.jpl.nasa.gov/science/mod3_SunlightSolarHeat/FusionChemistry (February 22, 2005) NASA ―NASA Solar Physics,‖ 2005, http://science.msfc.nasa.gov/ssl/pad/solar/cmes.htm (March 25, 2005) (Newton’s) second law SOHO ―The Solar and Heliospheric Observatory,‖ 2005, http://sohowww.nascom.nasa.gov (February 9, 2005) Southwestern Research Institute ―Interplanetary Magnetic Field,‖ 2005,
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http://pluto.space.swri.edu/IMAGE/glossary/IMF.html (February 23, 2005) Tony Phillips, PhD. ―Space Weather,‖ 2005, http://www.spaceweather.com (February 9, 2005) Todd Hoeksema, PhD. ―Solar Research Paper,‖ personal email (14 February 2005) University of Tennessee ―Sunspots,‖ 2005, http://csep10.phys.utk.edu/astr162/lect/sun/sunspots.html (February 8, 2005) University of Washington ―Analyzing a Coronal Mass Ejection from the Sun,‖ 2005, http://www.astro.washington.edu/larson/Astro101/CoursePak/lab03_solar_cme.pdf (March 23, 2005)
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By Rex A. Crouch
© 2005
16 April 20 05
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Abstract This is a brief look at our Sun, its creation, its structure, function, and some of the internal and surface characteristics of our star as well as recent developments in solar observations, and a few of my own personal experiments as they related to the Sun.
Introduction. Just less than 5 billion years ago, in a spiraling arm of our Milky Way galaxy, a cloud of gas, and dust began to compressing under its own weight. The particles within the cloud's core became so densely packed that they frequently collided, and fused together. The fusion process released tremendous amounts of heat, and light which could then compete with the force of gravity within the cloud. The two forces eventually found an equilibrium point, and a star was born. This star in question is our Sun. All stars in our galaxy and other galaxies come in various sizes and colors. All stars are relatively unique. Our sun is a medium sized star known as a yellow dwarf, or a G Class star on the Hertzsprung-Russel Diagram. Our Sun, located just 149,598,000 km from Earth has a radius of 696,000 km, a mass of 1.9891 X 1030 kg , and a surface temperature of about 5800 Kelvin. Our Sun is composed of (by mass), 74% hydrogen, 25% helium, and 1% all other elements. Because hydrogen has very little mass, the composition of the Sun by number of atoms would be 92% hydrogen, 7.8% helium, and 0.1% all other elements. The cloud from which our Sun formed did not use all of its gases and dust to make the Sun. The leftover gases and dust were used to form the planets of our solar system (Harvard Science Department, 2002). Our Sun has been fusing hydrogen into helium and providing Earth with radiant energy for about 4.5 billion years, and we expected it to continue doing so for another
4.5 billion years. Of course one day our Sun will expend it hydrogen to the point that it can no longer fight the force of gravity of its developing iron core. Gravity will then begin to compress the Sun under its own weight; yet again but the fusion process is changing as the Sun matures. The compression causes the new helium particles inside of the core to collide hard enough that they can stick together and fuse. The core then begins to fuse helium into carbon to create enough energy to maintain its balance with the force of gravity it is quickly growing iron core. Creating carbon gives off more energy than did the making of helium. The energy being pumped out of the core radiates through the outer layers of the sun. The introduction of too much energy into the sun’s envelope heats up the envelope particles to the point that the envelope expands. The Sun's envelope will expand and engulf all of the inner solar system out to the radius of Mars. In the process the Sun will drop in temperature; this change in temperature will be marked by a change in color as the star becomes a red giant. Our sun will continue to live like this for maybe another billion years before pulsating and exploding into a planetary nebula probably leaving a white dwarf at the center. That is the life and death of our Sun in a nutshell. Sun’s Structure. The structure of the Sun is like looking at a fascinating piece of machinery except is has no tangible moving parts. In the below image developed by the SOHO Project Team, we begin with the
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Sun’s Core where nuclear fusion that produces the heat and light we experience here on Earth occurs. Next we find the Radiation Zone followed by the Convection Zone. The Photosphere, which is what we typically see in one of the lower layers of the Sun’s atmosphere is the next layer. We next find the Chromosphere which is a reddish orange layer thousands of kilometers thick. Lastly we find the Corona which is the upper most layer of atmosphere on the Sun; this layer extends millions of kilometers thick. Other aspects depicted in the below image are a prominence, and flare which will be discussed in more detail later.
referred to as direct (University of Tennessee Astrophysics Department, 2005). Fusion Process. As mentioned in the introduction, the Sun is composed of predominantly hydrogen, then helium, and a small percent of all other elements. The fusion process, as mentioned, occurs at the Sun’s core where the temperature is believed to be about 15 million °C and the pressure of gravity can alter the nuclear bonds of atoms. Because of the extreme heat and gravity on the Sun the fusion process is more complex than the process here on Earth in that the fusion process is a step-by-step process called a proton-proton chain. In this fusion process two atoms of hydrogen are combined to create what is called helium-4 and energy. This occurs in several steps: The pressure at the Sun’s core forces two hydrogen protons to combine to form a deuterium. Deuterium is one hydrogen atom with one neutron, one positron, and a single neutrino. Heat is beginning in this step. A proton and a deuterium atom combine to form a helium-3 atom. A helium-3 is the combination of two protons with one neutron, and a single photon of gamma ray. Lastly, two of these helium-3 atoms join under pressure to form a helium-4. This consists of two protons, two neutrons, and two protons. This three step process accounts for about 85 percent of the sun's energy. The remaining 15 percent comes from the following reactions: A helium-3 and a helium-4 combine to form a beryllium-7 which is not the most stable form of beryllium. This consists of four protons and three neutrons, and a gamma ray. A beryllium-7, because of its positive nature, captures an electron to become lithium-7. Lithium-7 consists of three protons and four neutrons, and one neutrino.
SOHO Project
Sun’s Rotation. ―The Sun is not actually a solid body.‖ Subsequently its rotational period is not well defined. To imagine a sphere of water suspended and spinning about on an axis system; water would tend to spin faster in some placed than in others. The modern measurements the Sun rotates once about every 25 days near its equator, 28 days at 40 degrees latitude, and 36 days near the poles. The rotation is the same as that of the planets which is sometimes
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The lithium-7 then combines with a proton to form two helium-4 atoms. The helium-4 atoms have less mass than the two hydrogen atoms that started the fusion process. Subsequently the difference in mass was converted to energy as Einstein elucidated in his theory of relativity, (E=mc2). The energy is emitted in various frequency lengths to include gamma, extreme ultraviolet, ultraviolet light, X-rays, visible light, infrared, microwaves and radio waves. If you were conducting the equations in your head with empirical formulas you may have noticed that some neutrinos and protons were not accounted for at the end of the equation. These unaccounted for particles that fell out of the equations are emitted from the Sun and create the solar winds which will also be addressed with more scrutiny. Before continuing I want to mention that the word ―burns‖ although inaccurate when talking about stars is nonetheless a commonly used word to refer to the fusion process in the Sun or a star. In addition to the last three steps, the Sun also burns other elements at various temperatures at other layers within the Sun as depicted in the below graph:
Heat – radiation Light – radiation Bandwidths Sun’s Magnetic Activities. Magnetism is the key to understand the Sun. Magnetic fields are the cause of all features we see on and above the Sun. The direction of moving charged particles is changed by magnetic forces. This forces increased orbital speeds of some electrons and slows others; this also induces electrons to jump to higher orbits within atoms. These changes in electron speeds changes the light emitted in terms of frequency. These changes in frequency allow us to remotely measure the Sun's magnetic field by observing the difference in the energy of the light emitted as these electrons jump from orbit to orbit. Both strength and direction of magnetic forces are measured on the Sun however we still do not fully understand the Sun’s magnetic forces (NASA Solar Physics Department, 2005). Initially a Dutch physicist named Pieter Zeeman observed in 1896 that a spectral line splits when the atoms are subject to very intensive magnetic fields. The more intense these magnetic field the more intense the spits in the spectral lines. Between Zeeman and the works of George Hale, it was shown that sunspots occur where magnetic fields concentrate. The importance of the magnetic field of the Sun was becoming clearer. Astronomers began taking pictures of the Sun at two wavelengths, one just greater than the other and between the two pictures they could construct what is called a magnetogram in which the magnetic fields of the solar atmosphere are displayed. In these manetograms the dark blue colors
Temperature ~2 x 108 °K ~5 x 108 °K
~10 x 108 °K
He burning occurs C burning occurs myriad reactions 12 C + 12C —> 24Mg + occur 3 4He —> 12C + 20 4 Ne —> 4He + 16O He + 12C —> 16O + 20 4 12 C + 12C —> 23Na + Ne + He —> 1 24 4 16 20 Mg + He + O —> Ne H 12 C + 12C —> 20Ne + 2 20Ne —> 16O + + 4 24 4 20 Mg + He + Ne —> He 24 24 Mg + 4He —> Mg + 28 Si + 44 Ca + 4He —> 48Ti +
NASA table
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represented area polarized north while the yellow colors represented magnetic lines polarized south. The sunspots did not seem to relate however the magnetic lines did. By the 1960s the astronomer Babcock presented the magnetic-dynamo model. In this model the magnetic fields wrap around the Sun, kink, and eventually unwrap. The study of Helioseismology, addressed further in this paper, added further explanations to the phenomena of magnetism in the Sun. Ultimately, astronomers learned that the magnetic field of the Sun expanded deeper into space than anyone of them initially thought. Of the Sun’s magnetic characteristics that affects us most is the Interplanetary Magnetic Field. The interplanetary magnetic field is a part of the Sun's magnetic field that is carried into solar system by the solar winds. The interplanetary magnetic field lines are sometimes referred to as "frozen in" to the solar wind plasma. As the Sun does rotate, the interplanetary magnetic field, much like the solar winds, travels outward in a spiral. The interplanetary magnetic fields originate in regions on the Sun where the magnetic fields appear to extend indefinitely into space; these regions are sometimes referred to as ―open‖ magnetic fields (Southwestern Research Institute, 2005). The below image from Southwestern Research Institute assist in depicting this spiral pattern of the interplanetary magnetic field.
Southwestern Research
Along the Sun's magnetic equator, the opposite open field lines run parallel to each other and are separated by a thin sheet of current called the "interplanetary current sheet". Because of an offset between the Sun’s rotational and magnetic fields, the current is tilted as depicted by the image below.
The IMF is a weak field, varying in strength near the Earth from 1 to 37 nT, with an average value of ~6 nT. This interplanetary current sheet and interplanetary magnetic field extend outward dissipating over distance. The end of the effects of the interplanetary magnetic field is found past Pluto where the outgoing solar wind and the incoming plasma from interstellar space meet, this is called the
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Heliopause, or the boundary of our solar system. The Sun’s magnetic activities lead us into the surface features on the Sun caused by magnetic activities. Features on the Sun’s Surface The below image from reveals plumes, flares, plagues, and strongly depicts the lines of magnetic flux that twist, and turn the flaming gases over the surface of the Sun (SOHO, 2001).
Galileo Project
SOHO
Sunspots and Plagues. Sunspots have been monitored extensively for a long period of time allowing us to determine cyclic behaviors. Galileo first began monitoring the sun with the use of a telescope in 1610. He made an observation each day for 35 days at about the same time of day documenting sunspots. This affords us our first view of the motion of sunspots across the surface of the Sun. The following image was drawn by Galileo (Galileo Project, 1995. Galileo’s improper solar observations later led to blindness.
These sunspots are actually disturbances in the magnetic fields in which magnetic lines protrude out of the Sun inducing sunspots. These sunspots are areas on the solar surface that appear dark because they are cooler than the surrounding photosphere. They are about 4500 K which is about 1500 K lower than the temperature of the rest of the photosphere. The darkness is only relative. Should you view just the sunspot against the darkness of space it would glow brightly. The darkest region in the center of the sunspot is called the umbra and the region around the umbra is named the penumbra. These sunspots tend to fluctuate in intensity over a period of 11.1 years. This 11.1 year cycle is known as Solar Maximum and Solar Minimum. The activity of the Sun increases drastically at Solar Maximum exhibiting more sunspot and other surface phenomena during any other time. The below images depict the vast differences between Maximum and Minimum.
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groups; and k is a variable scaling factor (typically <1) accounting for observing conditions and equipment from binoculars to space telescopes. Scientists combine data from lots of observatories -- each with its own k factor -- to arrive at a daily value. The second system is called the "International Sunspot Number," which is provided by the Sunspot Index Data Center in Belgium. The Boulder and the International numbers are calculated from the same basic formula except they use data different observatories; regardless, if you were to divide the International Sunspot Number or the Boulder Sunspot Number by 15, you will reach about the same number visible through a standard telescope. Sunspots tend to end in two fashions; they either fade away as the magnetic line retract back into the Sun or the magnetic lines breakdown resulting in an explosion called a solar flare. Plagues. Plague is French for "beach‖. Plagues are bright cloud-like features found around sunspots that represent areas of higher temperature and gas density within the Chromosphere of the Sun. Plagues are visible when photographed through filters passing the spectral light of calcium or hydrogen. These plagues are an extended emission feature of an active region that exists from the emergence of the initial magnetic flux inducing the sun spot until the widely scattered remnant magnetic fields merge with the background. These bright features are found near almost all active sunspot groups, and occur on a larger scale, and are brighter than facula.
The below image depicts a quickly growing sun spot in the lower left portion of the image while the four small dots in the upper right are the remnants of a previously massive sunspot
Space Weather Image
In this image we see two sunspot numbers. There are specific techniques used to calculate these sun spot numbers. Of the two sun spot numbering systems in use today, the foremost is the "Boulder Sunspot Number," which is computed by the NOAA Space Environment Center using a formula created by Mr. Rudolph Wolf in 1848. In his equation, R=k (10g+s), where R is the sunspot number; g is the number of sunspot groups on the solar disk; s is the total number of individual spots in all the sited
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The below image depicts a sunspot adjacent to a plage. In the image the plages is the represented as the whiter area near the top. It is fascinating to see that the plague disturbs the field lines otherwise uniformly surrounding the sunspot.
create, depending on their intensity; violent solar winds that effect power grids here on Earth, spacecrafts, and even the Earth’s magnetic shield and atmosphere. These solar flares are divided into four classes in which X-Class is the most sever and B-Class is essentially benign (Phillips, 2005) Type Measurement is Intensity (I) in Watts/ m2
X M
Class Flare Class Flare
I 10 10 10
5 6
4
I 10 I 10
6
4 5
C Class Flare
Big Bear Solar Observatory
B Class Flare
I 10
Solar Prominences. Solar Prominences are features found on, at, or near the surface of the Sun. The term prominence, strictly by definition refers to protrusions, projection, protuberance, or surface abnormalities. In the realms of astronomy some consider prominences to be solar surface events caused by magnetic activities in the Sun while others tend to refer to all surface activities as prominences. For the purpose this paper, I will refer to all protrusions, projections, and protuberances as prominences. These prominences are predominately caused by magnetism in one or more ways. Magnetic activities will be responsible for most of the remaining items discussed here. Of solar prominences I will address: Solar Flares Filaments Hyder Flares Polar Plumes
Solar Flares are sometime mistaken for Hyder Flares which will be addressed under Filaments. Filaments. Filaments consist of relatively cool, and dense gas suspended over the Sun’s surface in magnetic loops. These filaments collapse when their magnetic fields become unstable or otherwise collapse. The following two images show the before and after collapse of a solar filament viewed from the perpendicular:
Solar Flares. Solar Flares are massive eruptions of gases near the Sun’s surface sending energy into space through the entire electromagnetic spectrum. These flares can
Space Weather
A solar filament when viewed from a profile appears to be a large standing flame—they
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can appear to be very dramatic as they hover over the surface as depicted in the image below taken using ultraviolet cameras.
originating from bright points near the limb extend 30 to 60 arcseconds above the limb. The ramification or significance of these Polar Plumes has not been fully addressed as of current date. The following two images taken by SOHO were at the 1032 Å wavelength (white light).
SOHO Project
Hyder Flares. Hyder flares, named for Charles Hyder, occur when magnetic field lines protrude through the Sun’s surface under the filament and breakdown the magnetic lines creating the filament. These can be observed, much like most flares, in the Hydrogen-Alpha wavelength of 656.3 nm. These explosions typically occur away from the spotted regions. As these are rare, they are typically mistaken for solar flares and there are few images available. Polar Plumes. According to Harvard University, Polar Plumes are collimated flow tubes, specifically ―magnetically unipolar, linear, high density structures‖, that may carry the majority of the mass and energy of the solar winds that emanate from high-latitude regions of the Sun’s Corona. These Plumes occur in regions of simple magnetic topology in contrast to the rest of the Sun. Plumes were original observed using white light but are also visible using extreme ultraviolet. Observation of Polar Plumes using the SUMER instrumentation on SOHO have indicated through use of spectroheliograms with 1.5 arcsecond steps extending to about 8 arcminutes that these Polar Plumes, narrow jets or macrospicules
SOHO Project
The following image was taken at 195 Å wavelength (extreme ultraviolet) clearly depicting the plumes near the polar regions as tiny jets:
SOHO Project
Coronal Mass Ejections. According NASA Solar Physics Department, Coronal mass ejections are very large clouds of gas and plasma threaded by magnetic field lines to the surface of the Sun and subsequently ejected from the Sun over the course of a
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few hours. These Coronal Mass Ejections disrupt normal solar winds and cause solar winds of their own. These ejections release billions of ton’s of material into our planetary space at speed in excess of 500 km/s. According the University of Washington, there may be more than 10 billion tons of electrified and charged gases erupting from the Sun during each Coronal Mass Ejection. The below image from SOHO depicts an intense Corona Mass Ejection from the Sun’s southern pole region.
The mass ejections are often directly associated with the sunspots, which always lie in the Sun’s equatorial belt or at mid-latitudes. Other mass ejections occur near the Sun’s poles, far away from any sunspots. These events are most frequent at the peak of sunspot activity, but they can continue for a while as the count of sunspots begins to decline.‖ The SOHO Project has compiled data as depicted below that shows an increase in Corona Mass Ejections during Solar Maximum and in terms of an increase we also see that speed of the ejections is nearly 300 km/s faster during Maximum then Minimum however, the variations in width are essentially unchanged between Maximum and Minimum.
SOHO
These Corona Mass Ejections are not random but rather a method that the Sun uses to clean-up unwanted magnetic fields left by Sunspots and other abnormalities (Australian Institute of Geoscientists, 2005). The Sun is in fact housekeeping and sweeping out the dust to paraphrase the Geoscience web site. ―What emerges is a systematic pattern in the outbursts. It changes during the sunspot cycle, as the numbers of dark sunspots seen each day on the Sun’s bright surface first increases and then diminishes again.
Solar Winds. The solar wind streams off of the Sun radially in all directions at speeds of near 400 km/s. The source of the solar wind is the Sun's super hot corona. The temperature of the corona is so high that the Sun's gravity can no longer retain it. Although the solar wind is always directed away from the Sun it is not uniform. The speed changes and the wind carries with it magnetic clouds and there are interacting
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regions where high speed winds catches up with slow speed winds, and of course there are composition variations of all of these factors. The speed of the solar winds vary greatly from as high 800 km/s to as low as 300 km/s. The solar winds from the poles has been measured to a limited extent in which the Ulysses Mission launched from Discovery went as far as Jupiter, and used the gravity of the planet to double back and pass over the south pole of the Sun 1994, and the north pole in 1995. The orbital pattern places the spacecraft over the solar poles once every 6 years. The Ulysses Mission found that there is an abundance of He3 in the solar winds, and deuterium in the outer convection zone during polar studies of the Sun. Not unknown to us but nonetheless confirmed the Ulysses Mission was that solar flares and class III radio burst are related to solar winds and solar maximum. Study of Features Internal to the Sun Helioseismology. At the Wilcox Solar Observatory at Stanford University the subject of Helioseismology is the developing subject for them. This is the science of studying wave oscillation within the sun. As the sun is not a solid object there is no one source of seismic waves. In lieu of a titanic plate as found on Earth it is termed the source of agitation causing solar waves and in most cases the source of agitation is the convective region. As this is one region it is treated as a continuum. The oscillations have amplitudes of no more than about 0.1 meters per second. The goal at the Wilcox Observatory is to measure shifts of a spectrum line to an accuracy of parts per million of its width (Hoeksema, 2005). The types of waves the helioseismologist are looking for fall into three types – Acoustic Waves, Gravity Waves, and Surface Gravity Waves.
Acoustic Waves. Generating p-mode oscillations. The p-mode oscillations or pressure mode oscillations are forms of acoustic waves – Consider the fact that the Sun is ringing but not like a church bell being struck once but rather a bell be struck by millions of little particles over a continuous span. There is not one loud ring but a constant trill of rings. In terms of oscillations, we are not discussing flat two dimensional oscillations, nor even three dimensional oscillations like the ripples seen on-top of water but rather three dimensional spherical oscillations known as p-mode (pressure mode) shaped oscillations. The p modes can be described in terms of spherical harmonics. The spherical harmonics are characterized by three whole numbers: The order, given by n in physics is the number of nodes in the radial direction. The harmonic degree is known as l and indicates the number of node lines on the surface. This correlates directly to the total number of planes slicing through the Sun. The third number, m, tells how many of the surface nodal lines cross the equator and also gives the phase. The term m has boundaries of -l to +l as the direction of the waves are important in many cases. The term m, describes the number of planes slicing through the Sun longitudinally. The oscillations are nearly radial. The frequencies depend on the travel time of an acoustic wave across the star. The below image depicts p mode oscillations in the l direction.
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Stanford Image
The next image depicts p-mode oscillations in the l and m direction. The p mode with this spatial pattern causes motion of the surface that alternate in sign (in or out of the surface) in adjacent regions. The difference between m=+/-18 is the phase (in or out) of the pattern. Note that we have essentially broken the Sun up into Earth equivalent of latitude and longitude.
Stanford Image
Gravity Waves. Generating gmode oscillations. According to Newton, for every action there is an equal and opposite reaction. For the p-mode oscillations, the reaction is the g-mode oscillations. These are the gravity mode oscillations or the thought of as the restoring force or gravitational force perturbation. Gravity mode arises because gravity tends to smooth out material inhomogeneities along equipotential level-surfaces of the Sun. As the p-mode oscillations are non-uniform, they are a form of agitation as such is the gmode oscillations, subsequently these oscillations are referred to as perturbations. Surface Gravity Waves. Generating f mode oscillations. Everything wants to vibrate at a frequency that specific to its shape and composition. For stars, this oscillation is the fundamental oscillation, the
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f-mode oscillation. The nature frequency of vibration. The f-mode (fundamental) is a stable mode which exists only for non-radial oscillations. The frequency is proportional to the mean density of the star. The f-mode can also be derived with Newton’s uniform density of stars formula.
2
2l l 1 M 2l 1 R 3
Each oscillation mode is but one sampling of the Sun’s interior which acts like a resonant cavity. Of the p and f modes there are about 107 modes which does not include n harmonics. The study of p, g, and f mode oscillations is serving to make the Sun transparent allowing deeper study of sun which brings us to projects that SOHO has been developing in which the internal rotation of the Sun is now being map. Observations by the SOHO Satellite. In direct correlation with Helioseismology is the internal mapping of the Sun’s rotation by the SOHO project as Dr. Fleck of the SOHO project elucidated with me. While we have known for extensive period of time how the out surface of the Sun rotated is has not been until recent technology allowed us to make the Sun transparent and look at the inner rotations. One of the most significant observations has been the rotation of the convection zone. In the below SOHO image we see the stability of the convection zone as a uniform rotation but varies drastically as it spans out from 0 to 90 degrees.
Another means of looking at the rotations shows that there are correlations between frequency ranges and time (in terms of days) within the Sun.
Recent Developments. There have been a multitude of recent developments in solar observation. Helioseismology Holography. As mentioned there is the growing and developing science of Helioseismology. Synoptic Imaging of Active Regions on the far side of the Sun using Helioseismology Holography to monitor condensations of magnetic flux allowing astronomers to monitor sunspots on the far side of the Sun and providing more accurate space weather.
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Corona In-Flows. Still under study are newly discovered Corona In-Flows in which matter traveling between 20 km/s and 100 km/s is falling back into the Sun through the Corona. These In-Flow rates correlated with the occurrence of non-polar coronal holes and other indicators of nonaxisymmetric open flux per SOHO Project members. Personal Experiments. For the purpose of developing my research skills I have opted to conduct several of my own experiments. As stated, the purpose is to develop my own research skills, and practice analyzing and documenting my findings. I don’t anticipate finding anything new but the application will be a learning experience for me nonetheless. Measure lambda and voltage monitored over a 200 meter antenna of 9.5 oriented parallel to the ground, and East West in direction. Measurements were conducted at various times of the day and night to discern any difference as the angle of the sun varied throughout the day. This experiment failed miserably as there was no way of discerning exactly where these long wave frequencies were originating or even isolating one frequency range to monitor. This experiment should be conducted again, except care should be taken to ensure that the antenna is shielded from stray RF, and a band-pass filter should be employed to examining one particular segment of low frequency at a time. Measure diameter of sun using a high frequency receiver. In measuring the diameter of the Sun using a 10 GHZ to 12 GHZ receiver on a parabolic dish I learned nothing new about the diameter of the Sun, but the experiment itself was interesting. I measured the distance across the dish and then I aligned the parabolic receiver to the Sun’s path. Connecting the receiver to a
recording device and a monitor I was able to visually discern when a change in intensity began. A time measurement from this point, and I terminated the time measurement when the signal intensity dropped. The Sun traversed the 72 cm dish in 4 hours and 24 minutes. Bisecting the dish into two right angle triangles this turned the experiment into a trigonometry exercise with a visual confirmation on an LCD screen. The Sun is in fact 1,380,000 km. Photovoltaic cell measurements. Measure intensity of various frequencies by using photovoltaic cells receptive to specific frequencies. The photovoltaic cells produce a voltage representative to the amount of light received in that bandwidth. The 525 Nanometer (nm) wavelength corresponds to the green light produced by our Sun. 626 nm is red light produced, and received by us here on Earth. I also conducted measurements at two infrared wavelengths being 816 nm, and 940 nm, both obviously out of our visual spectrum. The data table also shows air mass which is a based on 1.00 representing the mass of air directly overhead as the baseline. Measuring the angle of the Sun to your position can give you the mass of air the Sunlight must travel through to reach your measurement location. I also sought to compare voltage outputs of photocells to protons per centimeter cubed I collected the following data on 27 March 2005 during clear skies, and stable high barometric pressure: 37° rising Sun 525 nm 626 nm 816 nm 940 nm .425 V .452 V .519 V .508 V
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48° rising
Sun 525 nm 626 nm 816 nm 940 nm
.564 V .604 V .617 V .618 V .337 V .304 V .332 V .335 V .220 V .237 V .275 V .274 V light frequency
43° setting
Sun 525 nm 626 nm 816 nm 940 nm
33° setting
Sun 525 nm 626 nm 816 nm 940 nm
Conclusion of measurements:
The lower the Sun angle which corresponds to thicker air mass, the lower the output intensity of all bandwidths. This was obvious without an experiment, but was fascinating to see first hand to what degree the impact of sun angle has radiation received by a position here on Earth. The intensity of shorter wavelengths was higher than those in the visible light spectrum. This is something that I previously did not know and sparked some additional research on my part. Monitoring protons per cubic centimeter through SOHO as I conducted these measurements on the four light frequencies, I found no correlations to voltage outputs of the four frequencies examined and proton output by the Sun. Summary. In summary, I provided an overview of the subject matter that comprises our Sun. From the Sun’s birth out of stellar gas and search for an equilibrium in gravity and burn to become a star to the eventual death of the life-force in
our solar system. The basic structure and inner workings were dissected to gain an insight to how our star creates energy— looking at the fusion process from the chemical level we saw that the Sun converts hydrogen into helium and how this accounted for 85% of the Sun’s energy while the remainder came from burns of other various elements derived from the fusions process. The Sun’s Magnetic activities were then addressed covering the Sun’s basic magnetic features to the Interplanetary Magnetic Field that carries the solar winds. A glimpse at the features on the Sun’s surface was provided in which we looked at sunspots and various solar prominences. Corona Mass Ejections, Solar Winds, and touched upon the internal fusion machine as we delved deeper to touch on the inner workings through Helioseismology to find the internal rotations of our star. In contacting researchers from various solar research facilities I found them to be very helpful and insightful as I queried their recent developments. Recent developments were fascinating and I for one am waiting anxiously to see the results of the new studies. Lastly I touched on some of my own personal experimentation conducted for personal development. I found that a 6000 word paper on the Sun was truly a difficult subject in that the limitation of words was at a threshold in which we are just above layman talk, but skimming the advance scientific dialog. This paper turned-out to be a document in transition in which I learned a great deal about our Sun, and developed an appreciation for how much more this is to know.
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References Albert Van Heldon ―Galileo Project,‖ 1995, http://galileo.rice.edu (February 10, 2005) Amara Graps, ―Helioseismology,‖ 2005, http://soi.stanford.edu/results/heliowhat.html (February 14, 2005) Australian Institute of Geoscientists ―Predicting Solar Outburst,‖ 2005, http://www.aig.asn.au/solar_outbursts.htm (March 25, 2005) Bernhard Fleck, PhD. ―Dr. SOHO,‖ 22 February 2005, personal email (22 February 2005) Craig C. Freudenrich, Ph.D. ―How Stuff Works,‖ How the Sun Works, 2005, http://science.howstuffworks.com/sun1.htm (February 9, 2005) (Einstein’s) general theory of relativity Harvard Science Department, ―The Sun,‖ April 11, 2002, http://hea-www.harvard.edu/scied/SUN/sunpage.html (February 22, 2005) NASA ―Jet Propulsion Laboratory,‖ 2005, http://genesismission.jpl.nasa.gov/science/mod3_SunlightSolarHeat/FusionChemistry (February 22, 2005) NASA ―NASA Solar Physics,‖ 2005, http://science.msfc.nasa.gov/ssl/pad/solar/cmes.htm (March 25, 2005) (Newton’s) second law SOHO ―The Solar and Heliospheric Observatory,‖ 2005, http://sohowww.nascom.nasa.gov (February 9, 2005) Southwestern Research Institute ―Interplanetary Magnetic Field,‖ 2005,
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http://pluto.space.swri.edu/IMAGE/glossary/IMF.html (February 23, 2005) Tony Phillips, PhD. ―Space Weather,‖ 2005, http://www.spaceweather.com (February 9, 2005) Todd Hoeksema, PhD. ―Solar Research Paper,‖ personal email (14 February 2005) University of Tennessee ―Sunspots,‖ 2005, http://csep10.phys.utk.edu/astr162/lect/sun/sunspots.html (February 8, 2005) University of Washington ―Analyzing a Coronal Mass Ejection from the Sun,‖ 2005, http://www.astro.washington.edu/larson/Astro101/CoursePak/lab03_solar_cme.pdf (March 23, 2005)
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