Our Sun the Star
The sun is the center of our solar system and is a 4.5 billion years old star. The sun is a main sequence star and is approximately 870,000 miles in diameter. While the sun is just another star, it is by far the largest object in our solar system. "The sun has almost a thousand times more mass than all the planets, moons, asteroids, comets, and meteoroids put together".1 However, compared to other stars, the sun is the size and weight of an average star and about halfway through its life cycle. A stars color depends on its surface temperature, ranging from the hottest stars that are white or blue, to green, yellow, orange, and red is the coolest. The sun is a yellow dwarf star.
Eight billion years after the Big Bang the sun was born. After stars are born they begin a process of nuclear fusion. The stars start fusing atoms together in the order from lightest to heaviest. When the star runs out of one type of atom it will move to the next heaviest one. Stars, including the sun, first fuse hydrogen to helium, helium to carbon and oxygen, and then carbon and oxygen to a variety of elements. When the heaviest element runs out the star will die. However, the sun halts in the carbon – oxygen phase and scientist predict that it will be another 5 billion years before the sun dies out. When it does expand to become what is called a red giant and engulf most of our solar system2.
Scientific Activity 1: Don't be a Galileo
Internet Connection: The Sun
As part of the introduction to the sun, students can watch a short cartoon about the sun and take a mini quiz for reinforcement.
Mathematical Connection: How much is a million? How much is a billion?
Students are dealing with large numbers such as millions and billions. To improve number sense,
How Much is a Million?
by David M. Schwartz and illustrated by Steven Kellogg is a good way to introduce large number concepts to students.
In order to understand how the sun works, it is important to know that the internal structure of the sun is made up of three layers. Starting at the center and moving outward, the sun's inner most layer is called the thermonuclear energy core. The radius of the core is 30 % of the solar radius, i.e., it is about 130,000 miles thick. The center of the core has a temperature of27 million degrees Fahrenheit. The core, however, contains most of the mass of the Sun, about 94% of the mass. The energy generating core is a part of the next layer, the radiative zone of the sun. Together they cover 70% percent of the solar radius, i.e. about487,000 miles. Energy is transported by radiation in this layer (hence the name). The outward most layer is called the convective zone because energy transport in this region occurs by convection, which this through upward rising streams of hot material. It covers the outer 30% of the Sun, i.e., the remaining 130,000 miles. The temperature inside the Sun decreases steadily outwards through these layers, from 27 million degrees Fahrenheit at the center to a mere 9,900 degrees Fahrenheit at the surface 3, 4.
Scientific Activity 2: Layers of the Sun
Internet Connection: Internal and External Structure
This site displays an interactive diagram of the sun's internal and external structure and can be used to provide a visual demonstration of the sun.
Mathematical Connection: Fahrenheit, Celsius, and Kelvin
While for this unit, temperature is converted into Fahrenheit, as students read independently about this topic they will find that temperature is documented as Celsius and Kelvin. In order for students to understand they need to know how to make these conversions. Students can use the following conversions to determine the temperature in Fahrenheit.
Celsius to Fahrenheit – Multiply Celsius by 1.8 then add 32
Fahrenheit to Celsius – Subtract 32 from Fahrenheit then divide by 1.8
Celsius to Kelvin – Celsius plus 273
Fahrenheit to Kelvin – Convert to Celsius then add 273
Kelvin to Celsius – Kelvin minus 273
Kelvin to Fahrenheit – Convert Fahrenheit to Celsius and then minus 273
How the Sun Works
The sun is essential to life on our planet because of the light and heat that it provides. For centuries scientists hypothesized about how the sun actually created heat. Heat is a form of energy that travels from low to high temperatures. It was not until Albert Einstein's famous theory,
E = mc2
that astronomers were able to discover how the sun really works. Scientists determined that in the core of all stars, where there are extremely high temperatures, thermonuclear fusion can take place. The sun is comprised of mostly hydrogen and helium. Within the core energy is released through thermonuclear fusion where hydrogen is converted into helium. The energy travels from the internal part of the sun through two energy transport mechanisms known as radiative diffusion and convection. In the inner 70% of the sun (core and radiative zone), photons are carrying energy from one region to another. In the outer 30% of the sun (the convections zone), heat is transported through convection by which causes the circulation of fluids. Here, hot gases rise to the surface and cool gases retreat back to the interior. While it takes about 170,000 years for energy from the sun's center to reach the surface, it takes only eight minutes for that energy to travel from the sun to the Earth.
The sun's exterior has three layers. While there is no solid surface to the sun, the visible part of the sun is called the photosphere radiates at 9,900 degrees Fahrenheit. This inner most layer is where energy escapes from the sun. The photosphere is hot, but cool spots known as sunspots are found on this layer. Sunspots are magnetically active parts of the sun where the temperature is cooler causing it to look darker than the rest of the photosphere. While these spots look small, each sunspot is generally the size of the Earth. Sunspots can occur alone, but they generally appear in groups. The number of sunspots on the sun is somewhat predictable, they follow approximately an eleven year cycle ranging from many to few spots. Sunspots also continuously appear at the same latitudes on the sun and gradually move closer to the equator.
Internet Connection: Sunspots
At this site students can read about sunspots, as well as view pictures and a short film clip. This site also provides information about the history of sunspot, the solar cycle, and the connection to the Earth's climate.
Mathematical Connection: Measuring a Timeline
Relative to Sunspots
1610: Sunspots were discovered by Italian astronomer Galileo Galilei by using his invention, the telescope.
1833: E.H. Burrit discovered that different amount of sunspots were appearing at different times.
1843: Heinrich Schwabe discovers the frequency of appearance of sunspots and that they appear in cycles.
1852: Rudolph Wolf discovers that the sunspot cycle is 11 years long.
1908: George Ellery Hale determined that sunspots are associated with the sun's magnetic field.
The chromosphere radiates at 18,000 degrees Fahrenheit and is the middle section of the external sun. This small layer around the sun can be seen most clearly during a solar eclipse. The temperature in the chromosphere increases as one goes farther away from the sun, which is opposite of what happens in the photosphere. The chromosphere emits spikes of rising gas known as solar flares and prominences, and is the source of ultraviolet light. One manifestation of this activity is a prominence. Prominences are arching columns of gas released from the sun's surface that can last anywhere from a few hours to a few months. Complex sunspot groups can also be the cause of solar flares. Solar flares spread across the atmosphere in a rippling pattern that can affect life on Earth. These solar flares were discovered in 1859 by two scientists, Richard C. Carrington and Richard Hodgson5.
Internet Connection: Solar Flare
Both sites provide videos and pictures where students can view solar flares.
The corona which is much hotter than the surface of the sun, radiating at 3.6 million degrees Fahrenheit, is the white outer most section of the atmosphere. While the corona is hotter than the photosphere and chromosphere, it is lower in density causing it glow less brightly and actually "feel" cooler. The corona is the source of X- rays, solar wind, and coronal mass ejections. An outflow of gas through coronal holes in the corona cause solar winds. These winds are actually parts of the sun's mass being ejected into space. While this depletes the mass on the sun, the percentage actually being ejected is minuscule. The sun will lose only 0.01% of its mass through solar winds and coronal mass ejections in its lifetime. Coronal mass ejections can occur almost anytime, but are most intense during high sunspot activity. These ejections are a billion tons of high temperature gases being emitted towards the Earth. Because we cannot look directly at the sun, it was difficult to observe and study the corona. Generally, the corona can only be seen clearly during an eclipse, at other times the light from the photosphere hide it. However, in 1930 a French astronomer by the name of Bernard Lyot created an invention called the coronagraph that allowed astronomers to study the corona. Scientist no longer have to wait until a solar eclipse to get a look at the hottest part of the sun3, 6.
Internet Connection: Coronal Mass Ejections
Both sites provide videos and pictures where students can view coronal mass ejections.
Solar flares, solar winds, and coronal mass ejections can all affect our life on Earth. Before the invention of the telegraph, approximately one hundred and fifty years ago these solar particle events were not of great significance because we did not have the technology we rely on today. These events can affect the function of the artificial satellites that are in orbit around the Earth. There are five types of satellites: communication satellites which we use for television and telephone transmission, navigation satellites used mainly for military purposes but also for GPS locators, weather satellites which study the atmosphere, military satellites used to observe the earth, and scientific satellites to study the solar system. While our society has become reliant on these satellites, particles from the sun can possibly destroy them. For example, in October of 2003, solar flares destroyed a satellite from Japan that was being used for communication purposes7.
Solar events can also adversely affect astronauts. Radiation emitted by the sun can be hazardous to human health. Magnetic energy can disrupt radio waves and cause difficulties for traveling spacecrafts. Power grid outages are also known to occur because of the sun's forces. A strong magnetic storm caused approximately 17 % of Quebec to be out of power for nine hours in March of 19898, 9.
Internet Connection: Solar Energy Disrupts Life
Students can read about how solar events have effected or life on Earth.