The sun is such an integral part of our everyday life that we often take it for granted. For hams it has an additional meaning as well. Without the sun, and the sun spots it creates, long distance communications would be impossible. This is true for 20 meters up to the "Magic Band", 6 meters.

The sun provides the light that allows us to see, the warmth our planet needs, the source of our life. For hams it provides the needed level of atmospheric ionization to allow the bands to open. As we look deeper into the effects the sun has on us we also find that solar flares can cause Aurora which allow the VHF operator to work distances of a 1000 miles or more with a simple station.

Most aurora occurs near the North Pole. Here is North America we sometimes see Aurora in the more northern latitudes of the US and into Canada. Aurora is fairly common in places like Northern Canada and Alaska but it is only the really great auroras that reach down into New England, the Mid-Atlantic States and similar latitudes.

Let's look closer at our sun so that we can better understand how it impacts our daily lives but also how it effects radio communications.

· With the sun being deep in the vacuum of space, what keeps it burning?

· How is the burning contained within the sun?

· How long has the sun been burning?

· What causes the famous and sometimes disruptive solar flare?

· When will the sun run out of energy?

· Is our sun a typical star?

The sun is a common star and quite similar to other stars in the night sky. What makes our sun seem so different is it relative closeness to Earth. A mere 93,000,000 miles average distance. Now that is a huge distance, and one that would take a radio signal, traveling at the speed of light, about 8 minutes to reach it. Other stars we see in the night sky are 1000 times (or more) further away from us. When we talk of other similar stars we talk in terms of multiple light years away from Earth. A light year is a simple term. It means the distance a light wave (or radio signal) would travel in one year. The math is simple, 186,282 miles per second, times 60 seconds per minute, times 60 minutes per hour times 8760 hours per year. Not a small number by any means! And that is just one light year. Some stars are millions of light years away.

Scientists classify our sun as a G2 star based on its actual temperature. It is just a plain old average star, one of billions and billions of stars that are in orbit throughout our galaxy. Our galaxy is not the only one out there either.

The sun been burning for over 4.5 billion years and is expected to continue burning for another several billion years. It is a massive collection of hot gas made up of mostly hydrogen and helium. Because its mass is so great its gravitational field is millions of time greater then Earths. That is sufficient to hold all of hydrogen and helium within the sun. It also has sufficient gravity to keep the other planets (including Earth) in orbit around it. Quite an amazing feat.

The burning process of our sun does is not a typical burn like that of burning paper. It is instead a colossal nuclear reactor. Like a hydrogen bulb (if you will) continually burning at millions of degrees Fahrenheit.

What Makes The Composition Of The Sun?

The sun is entirely gaseous having no solid surface like here on Earth. It does have a very well defined structure. The major surface features are shown in the top of the drawing below:

· Inner Core

· Radiative Zone

· Convective Zone

Above the surface of the sun is its atmosphere, which consists of three parts as shown in the bottom portion of the drawing above:

· Photosphere

· Chromosphere

· Corona - extremely hot outermost layer extending several million miles outward

The most significant regions of our sun can be explained by understanding the nuclear reactions that generate its immense energy, the magnetic fields that are created as its gases move around the star, and its immense gravity.

Our sun is comprised of 3 primary regions:

The inner core region:

The radiative region:

The convective region:

Before we get to talking about sun spots, let’s first look at the basic makeup of the sun. From there we will get into sun spots and how they can impact radio communications.

The Inner Core Region:

The core region is at the very center of the sun and extends out to about 1/4 of the sun's radius. In this core region extremely strong gravity is continuously pulling all of the mass toward the center of the sun. This then results in very intense inward pressure. The pressure is plenty strong enough to squeeze individual hydrogen atoms hard enough to create nuclear fusion. The nuclear fusion that takes place results in the combining of 2 hydrogen atoms that are squeezed so tightly together that both helium-4 and energy are created. This is not a simple process but instead is a complex multiple step process. For those interested in the process, here it is:

1. Two protons combine to form deuterium (hydrogen atom with one neutron), a positron (basically an electron with a positive charge) and a neutrino. These are the things that have been talked about recently that pass through Earth as though it was not there. Scientists are working to measure neutrinos.

2. A proton and a deuterium atom combine to form helium-3 (two protons with one neutron) and a gamma ray, which is one form of X-ray

3. Two helium-3 atoms then combine and form helium-4 (two protons and two neutrons) and 2 protons.

These multi-step reactions make up about 85 percent of the sun's total available energy. The rest, around 15 percent, has the following source:

1. Helium-3 and helium-4 combine to form beryllium-7 (four protons and three neutrons) plus a gamma ray.

2. Beryllium-7 captures an electron to become lithium-7 (three protons and four neutrons) and a neutrino.

3. Lithium-7 combines with a proton to form two helium-4 atoms.

Since a helium-4 atom has less mass than two hydrogen atoms that started the process, the difference in mass gets converted into energy. Einstein's theory of relativity (E=mc2) explains this process. Energy emitted is in numerous forms of light including UV, X-ray, visible and infrared light, microwaves and radio waves. This is the source of where the microwave experimenter’s measurement of sun noise comes from. The sun also sends out highly energized particles known as neutrinos and protons. These make up what is known as solar wind. All of this energy reaches Earth and warms the planet, forces changes in our weather and even supplies the much needed energy of life. Earth's atmosphere protects us from most of these emissions.

Look at Figure 2. This image was taken by a set of special telescopes aboard the satellite SOHO that is designed to view various wavelengths of light emitted by the sun. It shows a composite image from a Michelson Doppler Imager and depicts rivers of plasma below the surface of the sun. The surface itself was imaged using an extreme UV telescope optimized at 304 Angstroms. These two images were then superimposed over an image from a Large Angle Spectroscopic Coronograph image. This device blocks out the image of the sun itself so only the corona is visible. An amazing image!

The Radiative Region:

The radiative region includes about half of the sun's radius starting at the core. In this region energy from the core is transported toward the surface by photons. Every photon emitted then travels about 1 micron (1 millionth of a meter). It then gets absorbed by a gas molecule. Following photon absorption, that same gas molecule becomes heated and then re-emits another photon exactly like the one it absorbed. This process of absorption and re-emission repeats itself over and over. Due to the extremely high mass involved, this repetitive process requires approximately 1025 absorptions and re-emissions prior to a single photon reaching the suns surface. It can take 100,000 years for energy to be released at the suns surface. Certainly a very slow process.

The Convective Region:

The convective region is the outermost third of the suns radius. This region is primarily composed of convection currents that carry energy to the surface. Convection currents are plumes of hot gas right next to falling areas of much cooler gas. Convection currents carry energy bearing photons toward the surface very quickly. Much faster than the radiative region transfers energy.

The Sun's Atmosphere is comprised of 3 parts:

· Photosphere

· Chromosphere

· Corona

Some Facts About The Sun

Average temperature = 5,800 degrees Kelvin (surface), 15.5 million degrees Kelvin (core) Kelvin and Centigrade are nearly the same for our purposes her.

Rotational period: 25 days (center) to 35 days (poles) This thing is BIG!

Orbital speed: 138 miles/second

Orbital period: 200 million years

The Photosphere:

The photosphere is the bottom most region of the sun's atmosphere. It is also what can be seen from Earth. It is approximately 200 miles deepwith an average temperature of 5,800 degrees Kelvin. Further from the core, the photosphere temperature cools and subsequently not as much light energy is emitted. Because of this cooling the very outer edge looks dark. This darkening is known as limb darkening and is viewed as a clear crisp edge of the surface.

Chromosphere:

The chromosphere is above the photosphere and about 1,200 miles deep. The temperature varies from 4,500 to around 10,000 degrees Kelvin. Though scientists are not certain, they theorize that the chromosphere is heated by a convection process starting in the photosphere region. Gases moving around in the photosphere, seem to produce shock waves which cause heating of surrounding gas that send millions of gas plumes shooting through the chromosphere. These plumes are known as spicules. A spicule may rise to 3,000 miles last only minutes. They may follow along magnetic field lines made by the movement of gases.

Corona:

The corona is the outermost layer of the sun and is several million miles deep. Normally this can not be seen from Earth except during a solar eclipse. Earth based X-ray images can also view the Corona. Surprisingly, Corona temperatures average 2 million degrees. Since this is the outermost layer logic would say it should be cooler, but it is not. Scientists seem to think it is due to the sun's magnetism. The corona region has both bright areas (hot) and dark (cooler) areas known as coronal holes. The much cooler coronal holes are thought to be locations where solar wind is released.

Solar Sunspots, Prominences and Flares

Since the human eye is not equipped to look directly at the sun we must use telescopes and other devices to do our direct viewing.

Sunspots:

Dark, cool areas (sunspots) appear on the photosphere. Sunspots occur in pairs and are areas of extremely intense magnetic fields that are thousands of time greater than that on Earth. A sunspot forces its way to the surface and magnetic field lines exit from one sunspot of the pair and then re-enter through the other sunspot. Sunspot peaks and valleys are part of a well known 11-year solar cycle. During these cycles we experience periods of maximum and minimum sunspot activity. The cause of the 11-year cycle is not fully understood but one two theories may explain it:

· Uneven sun rotation may distort magnetic field lines deep within the sun. The distorted magnetic field lines might break through to the surface and form each sunspot pair. At some future time field lines break down decreasing activity. 11 years later the same cycle repeats itself.

· Gargantuan columns of hot gas encircle the interior of the sun at high latitudes and then slowly drift closer to the equator where they then collide with each other and form sunspots. Once reaching the equator, they break apart. This is followed by a decline in the number of sunspots. See Figure 3

Solar Prominences:

Since the sun is a very dynamic environment intermittently huge gas clouds from the chromosphere will rapidly rise aligning themselves along magnetic field lines of a pair of sunspots. (Figure 4). A single prominences can last 2-3 months and can reach an altitude of more then 30,000 miles above the surface. Once they reach an high altitude prominences can erupt for a few minutes or hours sending huge volumes of material racing through the corona. They then leave the sun’s atmosphere and race into space at 600 miles/ second. An eruption is known as a coronal mass ejection.

Solar Flares:

Sometimes very intricate sunspot groups abruptly erupt creating a violent ejection of energy. Solar flares most likely are caused by sudden changes in concentrated areas of the sun’s magnetic field. Solar flares are complex events that include the release of gas, electrons, visible and UV light plus X-rays. Of great interest to a ham is when radiation and particulate from a solar flare reach Earth's magnetic field. Here they interact with Earth's magnetic field at the poles and often produce an aurora borealis. See Figure 5.

A single solar flare can wreak havoc on radio communications. The impact of a solar flare can affect direct radio communications, satellites, navigational equipment and even a power grid. Radiation and particles that reach Earth can ionize the atmosphere and restrict radio signal flow to and from Earth orbiting satellites and Earth based stations. Highly ionized particles that enter our atmosphere can induce electric currents in power lines (much like a transformer would do) and cause power surges. If a power surge is severe enough it in turn can overload a power grid and cause blackouts by tripping automatic safety devices such as circuit breakers built into a modern power distribution system.

What Lies Ahead For The Sun?

As we mentioned at the top of this page, the sun has been burning for something on the order of 4.5 billion years. In spite of this it still has a sufficient amount of hydrogen fuel to continue for about 10 billion years more. None of us have to worry about this in our lifetime! The sun is simply operating within a balanced set of conditions between the outward pressure made by the release of energy of the nuclear fusion process and the inward pull of gravity. In a few billion years the sun’s core will run out of hydrogen to fuel continued burning. At that point it will begin in implode on itself due to its intense weight of gravity. A small amount of hydrogen fusion will take place in the upper layers. As the core continues to implode on itself the core will heat up and in turn heat the upper layers. This heating will cause these upper layers to greatly expand. With continuing expansion the size of the sun will increase and it will then become a red giant. As a red giant star it will come very close to Earth and Earth will get pulled into the core of the sun and be vaporized. Later on in the normal process of a dieing star, the core will heat sufficiently to cause the helium to fuse into carbon. Following that process, and once all helium fuel has been used up, the core will expand and cool. As the upper layers also expand they will eject material out into space. In the final step of the process the core will cool and turn into white dwarf star and then into a black dwarf. The entire process will take a several billion years. So anyone still remaining on Earth will have some warning.

Reading this may have left more questions then it answered. For additional information you will have to do some research.

So let the sun rock on………