Life on Earth would not have been possible were not for the process of star formation that has been continuously occurring since the Universe began to expand some 13-15 billion years ago. Each star evolves in a slightly different way depending on the initial mass of the star. Stars begin their life as a vast cloud of dust and gas (mostly hydrogen gas). Gravitational forces bring these particles and gases together until the conversion of gravitational potential energy to heat causes the temperature to raise enough to allow hydrogen fusion. Once hydrogen starts fusing into helium, a star is born.
While all stars form in the same way, the path a star takes to its eventual death is not always the same. How a star ends its life is dependent on its initial mass. Low mass stars (about five times the mass of the Sun or less) will evolve and end their life as a white dwarf. Intermediate mass stars (five to ten times the mass of the Sun) will evolve and end their life as a neutron star while the most massive stars become black holes.
Life on Earth owes its existence to the process of stellar evolution, for without it our sun would never have been created and therefore never have been able to bathe out planet with its life giving energy. It should be noted, though, that it is this same process of star formation and death that will some day be the demise of the Earth and all life on it. Current measurements suggest that the Sun is halfway through its ten billion year life cycle. It has continuously increased its heat energy output over the past 5 billion years and will continue to for the next 5 billion years.
In addition to addressing the concerns and questions that my eight-grade students have about stars, how they form, how they die, and what that means for life here on Earth; the development of this curriculum unit will also be guided by the New Haven Public School scientific inquiry performance standards that state that students will identify questions that can be answered through scientific investigations, that students will develop descriptions, explanations, predictions and models using evidence, and that students will recognize and analyze alternative explanations and predictions about the world around them. Also aligned with the unit are New Haven's Earth Science performance standards, which state that students will describe the features of our sun and how it compares with other suns in the universe and that students will describe other effects of the sun's energy on our world such as weather and winds, the growth of plants, and the water cycle. Using these standards as a guide, I will focus on, and develop the following topics related to stellar evolution for the classroom: 1) The sequence of events as stars form, "burn" their fuel, and then end their life, and 2) The fate of our Earth as our own sun progresses through its evolution.
The first lessons in the unit will be themed around the life cycle of stars. Stellar life cycles are determined mainly by how much mass the star initially has. A high-mass star will eventually become either a neutron star or a black hole, while a low and intermediate mass star will end its life as a white dwarf. I will use a hands-on strategy to teach this topic. One activity will involve the students choosing a known star and then illustrating its life cycle based on what its initial mass was. The students will be responsible for describing each stage as well as illustrating it on paper. In addition, they will determine if their star's evolution would change if it started with one half, and twice, its true initial mass.
The second area of focus will be on Earth and how the sun's evolution will affect it. Again my strategies for teaching will include hands-on activities such as creating models of the sun in various stages of its evolution. However, there will be more of a focus on mathematics and determining how much material the sun is burning and how long the sun will continue to do this. In building on previous knowledge and skills, the students will once again determine how our sun's fate changes if it had started with one half, and twice, its true initial mass. As the students grasp the processes of stellar evolution, we will look at how Earth is affected by this process. The students will answer the central question of how does the sun's fate effect the Earth's fate. The students will construct a timetable that will show the interactions of the sun and Earth as the sun evolves.