Sun

Astronomy Unit two- The SUN

While many astronomers refer to our sun as a typical or ordinary star, it is brighter, larger, and more massive than the majority of stars. Suns diameter is 1,400,000 km. Four times the disance to the moon Circumference= 4million km Sun's mass= 1000 times that of jupiter and 300,000 times the mass of the earth

Sun's mass compared to the earth is like comparing 3 nfl linebackers to a paperclip

99.9% of the atoms in the sun are either hydrogen or helium If you could take out all the calcium in the sun, you could craets an earth sized planet with it. You could do the same with the sun's copper, silicon, chlorine, fluorine, potassiem and many other elements. Gold ranks 77 in the order of elements in the sun, but you could take all the gold and plate the earh to a thickness of 100m

Energy output of the sun = 4x10 to the 26th power watts If one second worth of the suns energy could be captured converted to electricity, and sold at 5 cents per kilowatt hour it would bring in $6x10 to the 18th power

why study the sun? 1. Becuase nearly all the energy ever used was derived from the sun, and it is imporant to know how long it will last. 2. it is the closest star to us and we can infer that the processes happening in our sun are also happening in other stars

Internal structure of the sun

astronomers have been able to calculat4e the conditions inside the sun through mathematical formulas pressure temperarue mass, luminosity are all calculated and predicted as to how they change with distances rom the center of the Sun. To solve the equations, some info was needed chemical composition; mechanism by which energy is carried out of the sun; rate of production of energy at each distance from the suns center.

Internal Structure

Center of the sun= 15.6 million kelvin (same as celsius, starts at -273 C= 0K Gas at center of sun compressed to density of 150 time the density of water. All of Sun's energy is produced in the first 25% of the radius from the center. This is due to the requirements for the nuclear reaction that takes place. By the 1/4th mark from the center, the temp has fallen to 8million k (nearly half as hot as the center) At beyond the 25% radius, virtually no energy is produced. the rest of the sun is involved in transfer of the energy produced from the center to 25% radius.

At the sun's surface, Hydrogen makes up 71% of each kilo of gas. At the center of the sun, hydrogen only makes up 34% This occurs because the sun is about halfway through it's hydrogen fuel supply

Sun's Energy Geological evidence shows that the sun has beeen heating the earth for at least 3.5 billion years probably the sun has been shining for as long or onger than the earth has been around there have been many attempts at explaining how the sun produces energy.

Until the mid 19th century, not muc thought was given to how the sun produces its energy, as knowledge of physics and chemistry was limited.

Willian Herschel (leading astronomer of his time) suggested that sunspots were holes in the sun's fiery cloudsm through which he could see a cool surface "lush with green vegetation"

The idea that the sun is burning has been around since ancient times. Combustion, a chemical reaction, can produce a great deal of energy. We now know that if it were hydrogen burning in oxygen, the Sun could have remained burning for only 2000 years. Lord Kelvin, in 1862, suggested that the brightness of the Sun was from meteoric impacts. Objects falling into the sun accelerate and their energy is converted to heat and light.

We now know that it would take about 1/10th of the mass of the earth striking the sun each year to produce that amount of heat and light. If the much mass were striking the sun every year, it would now be seen via telescopes, and that increase in mass of the sun would hace a greater gravitational effect on the entire solar system, changing orbits.

Gravitational Contraction 19th century idea as to the source of the sun's power was that it was slowly falling in on itsself due to its own gravity. This is the souce of the luminosity of both jupiter and neptune.

Problem: sun couldn't do that for long enough. If the sun began as a widely dispersed cloud of gas and the shrank to its present size, the total energy released would only be enough for 20 million years.

This amoung of time (20 mil yrs) for the sun to have shrank to its present size is called the Kelvin-Helmholtz time

When this theory was proposed, 20 million years was believed to be enough time to account for the history of the solar system.

We now know that the Sun has been shining for about 200 times that length of time.

Beginning of the 20th century- realization that cast amounts of energy could be released in uclear reactions

according to einstein's formula E=mc2 fission of even a small amount of matter could yield large amounts of energy.

1 kg of fissionable material yields about 1 million times as much as 1 kg of combustible material.

While fission seemed like possible explanation for the sun's energy, the amount of fissionable material in the sun is relatively low.

Uranium makes up only about one in every 10 to the 12th power atoms. Fission of Uranium could only power the sun for about two months.

The process involved in powering the sun had to deal with the elements that are abundant in the sun.

1920- A.S. Eddington proposed that the process fueling the sun was the fusion of hydrogen into helium. It took 20 ears to work out all the details.

Sun's lifetime- fusion is more efficient than fission and far more efficient than conbustion. Fusion of 1kg of hydrogen into helium is about 10 times as much as fission of 1kg of fissionable material and more than 10 million times that of combusting 1kg of fuel. Sun consumes 6x10 to the 11th power of hydrogen per second.

Basic formula for Sun's energy production

Nucleus+nuclueus 2-> nucleus3+energy Key part is ENERGY that results from the reaction It is also key to realize that the mass of nucleus 3 is less than the added masses of nucleus 1 and 2. Law of conservation of mass is still in play as the excess mass is converted to energy.

In the case of fusion reactions in the core of the sun, the energy produced primarily is in the form of electromagnetic radiation The light we see coming from the sun means that the suns mass must be slowly but steadily, decreasing with time.

Solar Structure

The sun has a surface of sorts that we call the photosphere

THis is the part of the sun that emits the radiation we see. The radius is about 700,000 km, but the thickness is only about 500km less than .1% of radius Temps here=5800 kelvin

Just above the photosphere is the chromosphere, the sun's lower atmosphere

It is about 1500km thick Temps here are at 4500 kelvin

Next layer baove the chromosphere is the transition zone. This zone exists from 1500 km to 10,000 km above the photosphere Temps here are about 8000 kelvin (hotter than lower level)

Above 10000 km and stretching far beyond is the thin hot upper atmosphere; the solar corona. Temps here reach 3,000,000 kelvin.

At greater distances, the corona turns to solar wind, which flows away from the sun and permeates the entire solar system.

Extending from the photosphere inward, down some 200,000 km is an area of the sun called the convection zone.

Temps here=2,000,000 kelvin Material here is in constant convective motion.

Below the convection zone is the radiation zone In this zone the energy is transported by radiation from the core to the convection zone Temps here= 7,000,000 kelvin

Below the radiation zone is the sun's core here is where the nuclear fusion is taking place. Here temps are at 15,000,000 kelvin Highest density.

SUNSPOTS AND SOLAR MAGNETISM The dar roundish markings in the photosphere are called sunspots Often they are large enough to be seen without a telescope(reports in ancient chinese writings) They range in size from 2500 km across (lasting less than an hour) to as large as 50,000 km across (four times the diameter of earth) large ones can last for months darkest part of a sunspot is the umbra area around the umbra is the penumbra

large spots can occur if smaller ones combine. spots tend to occur in sunspot groups area around a group is called an active region, as solar flares and other events occur there galileo observed sunspots with his telescope by aiming the telescope in reverse to porject the image onto a screen. He noticed the the sun must rotate as the sunspots moved around the sun.

unlike the earth the sun doesn't have a single rotation period. ( the earth takes 24 hours to make a rotation) Sun's rotation depends on latitude near the equator of the sun, the rotation is about 25days. as you go towards the poles of the sun, the times gets longer. at the poles, the rotation is about 36 days. this phenomenon is called differential rotation and has important consequences for the sun's magnetic field.

> Solar Flares
 * Abrupt releases of solar magnetic energy
 * take place in active regions where prominence is supported against gravity by magnetic field lines
 * when magnetic field structure changes abruptly, large numbers of of ions and electrons are produced
 * some of these ions and electrons collide with the coronal gas, heating it to temps as high as 40,000,000 Kelvin!!!!!!
 * for several minutes, the heated gas emits mostly x-rays and ultraviolet radiation.
 * When X rays and UV radiation reach the earth (8 min. later) they ionize atmospheric gases, disrupting long range radio communication.