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Lets Study the Sun!

Studying the Sun is a fascinating topic for people of all ages, a provides a foundation for understanding many earth science topics. Some good pictures of our glorius Sun can be found at the website http://seds.lpl.arizona.edu/nineplanets/nineplanets/sol.html.

Table of Contents

  1. Observe the Sun (project)

  2. Sing a Solar Song (project)

  3. Basic Facts about the Sun

  4. Structure of the Sun

  5. Sun Gods

  6. Sun Info Websites

Observe the Sun

You can easily and safely observe the Sun by projecting it through a tiny hole onto a white sheet of paper. This simple device is called a "pinhole camera". You'll need:

With the pin, punch a hole in the center of one of your pieces of paper. Go outside, hold the paper up and aim the hole at the Sun. (Don't look at the Sun either through the hole or in any other way! ) Now, find the image of the Sun which comes through the hole. Move your other piece of paper back and forth until the image rests on the paper and is in focus (i.e. has a nice, crisp edge). What you are seeing is not just a dot of light coming through the hole, but an actual image of the Sun.

Experiment by making your holes larger or smaller. What happens to the image? What happens when you punch 2 holes in the piece of paper? Try bending your paper so the images from the 2 holes lie on top of each other. What do you think would happen if you punched a thousand holes in your paper, and you could bend your paper so all the images lined up on top of each other?

In fact, optical telescopes can be thought of as a collection of millions of "pinhole" images all focused together in one place!

If you want, you can make your pinhole camera fancier by adding devices to hold up your piece of paper, or a screen to project your Sun image onto, or you can even adapt your pinhole camera into a "real" camera by adding film.

Sing a Solar Song

The following funny song, author unknown, was apparently written in the 1950s to promote nuclear power. A recording of this can be found on the album "Why Does The Sun Shine?, Live!!", New York City 10/14/94, by the band They Might Be Giants:

Lyrics:
The sun is a mass of incandescent gas,
A gigantic nuclear furnace
Where hydrogen is built into helium
At a temperature of millions of degrees.

Yo ho, it's hot - the sun is not
A place where we could live;
But here on Earth there'd be no life
Without the light it gives.

We need its light, we need its heat,
We need its energy;
Without the sun, without a doubt
There'd be no you and me.

To hear the melody, listen to a recording, available on this NMSEA webpage compliments of the Unofficial They Might Be Giants website (www.tmbg.org).

Basic Facts about the Sun

What kind of heavenly body is the Sun?

The sun is a star, that is, a luminous ball of concentrated gas in space. The sun is our nearest star, and in particular, is the star that our planet Earth orbits around, along with the other eight planets in our solar system.

What is the Sun Made of?

All matter is made up of atoms, and atoms are made up of smaller particles, called protons (which have positive charge), neutrons (which have neutral charge), and electrons (which are negatively charged). Electrons orbit around the center, or nucleus, of atoms, just like the moon orbits the earth. The nucleus is made up of neutrons and protons.  

The element hydrogen, the first element of the periodic table, is made up of a nucleus consisting of one proton and one neutron, and this nucleus has one electron orbiting around it.

The element helium, the second element of the periodic table, has two protons  and two neutrons in its nucleus, and two electrons orbiting around it.

The Sun is presently made up of about 75% hydrogen and 25% helium (by mass; by atoms, its about 92.1% hydrogen and only 7.8% helium). As the Sun ages, more and more hydrogen gets converted to helium.

When was it made?

The Sun condensed out of interstellar gases (mostly hydrogen) about 4.5 billion years ago.

Distance of the Sun from Earth

The Sun is about 93 million miles from Earth. Although sunlight travels at 186, 282 miles per second (about 671 million miles per hour!) it still take about 8.2 minutes for sunlight to reach us. Another way to look at this is as follows. 

Suppose you were drive a car from the Earth to the Sun at 70 miles per hour. Then, it would take you 93,000,000 / 70 = 1,328,571 hours. How many years is this? Well 1,328,571 hours divided by 24 hours per day, and then by 365 days per year, yields 151 years!   

Mass of the Sun

The Sun has a mass of about 2 x 1030 kilograms, and so would weigh about 4 x 1030  pounds at the Earth's surface (of course, there would be no Earth's surface if the Sun came here! but anyways...).  Thats 4, followed by thirty zeros, or 4 million million million million million million pounds. It contains more than 99.8% of the mass of the solar system, so Earth is just a tiny speck (Jupiter contains most of the rest - so Earth is just a tiny tiny speck!)

Size of the Sun

If would take about 109 Earth's, lined up end to end, to equal the diameter of the Sun. Therefore, if you draw a picture of the Sun on the blackboard, with a diameter of about 1 meter, then the Earth would be circle with a diameter of a little less than 1 centimeter.

What will happen to the Sun eventually?

Eventually, the Sun will use up all the hydrogen in its core, and then will start to use up hydrogen outside the core. When this happens, the Sun will grow to 100 times its present size, and become 500 times more luminous (the Earth will become a molten ball at this point). At the point, the Sun will quickly use up its remaining energy, and finally explode, probably ejecting about one third of its mass out into space. A "planetary nebulae" will probably then remain (a slightly luminous cloud of gas), surrounding a tiny and very dense "white dwarf" star. The white dwarf will gradually cool down, leaving behind a "black dwarf". 

 In this project description, we begin by listing a few suggestions for Sun study. We then provide you with a fairly comprehensive description of the concepts, statistics, and examples you will need.

Structure of  the Sun

The Sun's Core: power plant of the Sun

The Sun's core is about 15 million degrees Kelvin (about 27 million degrees Fahrenheit), and 12 times denser than lead (150 times denser than water).

The pressure at the core is about 250 billion times that on Earth!

All the energy radiated by the Sun is  produced in the core by "fusion", a nuclear reaction wherby hydrogen nuclei are fused together to form helium. When this occurs, some of the matter making up the hydrogen is actually converted to energy. The amount of energy can be calculated from the amount of matter converted by Einstein's famous equation

  E = m c2 ,

where E stands for energy, m for mass, and c is the speed of light. Fusion occurs only in a volume of about only 1% of the Sun's total volume (which defines the core). The Sun is fairly weak compared to many stars - its classified only as a G2 or "yellow drawf" star (stars are classified with the letters O, B, A, F, G, K, M - O stars are the hottest, M stars the coldest, the numbers following the letters are just further subdivisions). Even so, the amount of energy given off by the Sun is still enormous by human standards  - equivalent to about one thousand, one megaton thermonuclear bombs going off every second! In watts, the unit of measurement we use for light bulbs, the Sun puts out about 386 billion billion million watts. Amazingly, even with this enormous output, the Sun has used up only roughly half its energy over its 4.5 billion year lifetime, so it would still take several billion more years for the Sun to burn all its energy up at its current rate of usage. Some scientists now think that the Sun may burn out sooner than another 4.5 billion years, but don't worry, its still not likely to happen for hundreds of millions of years!

Convection Zone

This is the region from the Sun's core out to the Photosphere (see the next paragraph) wherein convention currents and radiation transfer over short distances carries energy generated in the core out to the photosphere, much like the currents in a pot of hot water convect energy from the pot's bottom to the surface.

Photosphere

The surface of the Sun, defined to be point at which energy can first escapes the Sun (basically, its the part we see when we look at the Sun), is called the "photosphere", and is actually consists of a gas which is only about 1 millionth the density of water (about one thousanth the density of air).

The temperature of the photosphere is about 6000 degrees Kelvin (or about 10,305 degrees Fahrenheit). The Photophere is to a good approximation what physicist's called a "blackbody radiator", that is, it radiates light with a spectrum nearly identical to that which a dark colored object (say, a solid rock, for example) would radiate if it also had a temperature of 6000 degrees Kelvin (see the section on blackbody radiation in the .

Gravity on the Sun's surface is about 27 times that on the Earth's surface. Thus, a person on the Sun's surface would weigh about as much as an elephant!

Chromosphere 

A small region just outside the protosphere which is not much hotter than the photosphere (but yes, it is hotter even though its further out!). The chromosphere has a redish glow.

The Corona

The corona is a layer of gases around the photosphere that extends millions of miles out into space. These gases are trapped and controlled by complex magnetic field loops, which also give rise to spectacular solar flares. Interesting, the temperature of the corona is generally much higher than that of the chromosphere and photosphere, reaching temperatures of about a million degrees Kelvin (about two million degrees Fahrenheit).  This is thought to be an effect of the Sun's magnetic field. 

Sunspots

Sunspots are cool spots on the Sun's surface, and hence appear darker, which are cooler because convection of heat from the interior has been inhibited by a high magnetic field concentration that has developed there. They can be a large as 35,000 miles in diameter, and their number varies periodically on about an 11 year cycle, a period called "the solar cycle".

Solar Wind

A stream of particles and gases, mostly protons and electrons, that stream from the Sun's corona at around 350 kilometers per second. 

Solar Flares 

Solar flares are intense bursts from the Sun's surface of charged particles and electromagnetic radiation, including X-rays, gamma-rays, visible light, and radio waves. They can occur very quickly (in the space of minutes), usually last less than 12 hours,  and typically release about 1/10 as much energy as the Sun releases on average in one second This is powerful enough to disrupt satellites and other systems on Earth. The first solar flare was seen observed in 1851.

Prominences 

Prominences are gigantic loops (several times larger than the Earth's diameter) of cold material trapped in magnetic loops in the Corona, that can sometimes live for months at a time. They were first discovered during solar eclipses.

Sun Gods

Almost every ancient culture worshiped the Sun in one way or another. 

Ra was the Egyption God of the Sun.

Helios was the young Greek God of the Sun, son of Hyperion and Theia. Each morning at dawn he rises from the ocean in the east, riding in his chariot, pulled by the four horses Pyrois, Eos, Aethon, and Phlegon, and descends at night into the west. He sees and knows all, and was called upon by witnesses. Helium is named after helios because it was first discovered as a new element that existed in the Sun

Sol was the Roman's name for Helios, where we get the term "solar".

Sun Info Websites

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