Scope, Sequence, and Coordination

A Framework for High School Science Education

Based on the National Science Education Standards


Starlight

Gravitation, Star Processes, and the Formation of the Elements
Early in the history of the universe, matter, primarily the light atoms hydrogen and helium, clumped together by gravitational attraction to form countless trillions of stars. Billions of galaxies, each of which is a gravitationally bound cluster of billions of stars, now form most of the visible mass in the universe.

Stars produce energy from nuclear reactions, primarily the fusion of hydrogen to form helium. These and other processes in stars have led to the formation of all the other elements.


Further Description:

A star is an object whose energy is generated in its interior by nuclear reactions. Stars have been named using a variety of systems. Some have Arabic names (Beetlejuice); some have Greek letters, particularly those in constellations (Alpha Centauri); while others are known by English letters followed by constellation names or by catalog numbers (T Tauri).

There are nine basic properties of stars that can be measured. Through trigonometric parallax, distance of near stars can be determined. When distance is combined with brightness, luminosity can be measured. Spectra provide measures of temperature, composition, rotation, circumstellar materials, and motion. Luminosity and temperature can be used to determine the diameter of a star. By using the measures of binary stars and Kepler=s laws, the mass of a star can be determined.

Due to their great magnitude, star distances are measured in light-years and parsecs. Stellar spectra provide a real key to many of the properties of stars. Both the Doppler effect and the Stefan-Boltzmann law are used in interpreting spectral data. Star brightness has been defined by apparent magnitude and absolute magnitude. These systems attempt to classify stars according to their brightness.

Stars come in a great varietyCmassive, not massive, bright, not bright. They pass through an evolutionary process. For very massive stars the end of that process is an explosion, a supernova. In addition, stars of different initial mass evolve at different rates.

Theoretical studies indicate that stars form by the contraction of an interstellar gas cloud that is so hot that atoms at the center collide at extremely high velocities. These collisions cause nuclear reactions in which hydrogen atoms are fused into helium atoms, releasing energy. A battle begins between gravity squeezing down on the star and the radiation pressure pushing out the star. As a star begins to age and run out of fuel (hydrogen), the nuclear process is modified and gravity begins to win the war.


Concepts Needed:

Grade 9

Many of these concepts can be learned at this level only in a very qualitative manner or with analogy or metaphor: white dwarf, pulsar, neutron star, blue giant, red giant, black hole, nova, supernova, stellar colors, coalescence, stellar evolution, chemical elements, luminosity, EM spectrum, emission spectroscopy, radiation pressure.

Grade 10

Star map, constellation, groups of stars, types of stars, luminosity, star distances

Grade 11

At this level, the concepts listed above should be made more quantitative, involving, when possible, terms, facts, equations, and other aspects of more advanced physics and chemistry.

Grade 12

White dwarf, pulsar, neutron star, blue giant, red giant, black hole, nova, supernova, stellar colors, coalescence, stellar evolution, chemical elements, luminosity, EM spectrum, emission spectroscopy, radiation pressure


Empirical Laws or Observed Relationships:

Inverse square law of light, Wien=s law, types of stellar fusion (proton-proton, triple alpha)


Theories or Models:

Gravity, Stefan-Boltzmann law, photon theory of light, origin of elements, theory of star formation, protostar


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Micro-Unit Description:

Starlight
Grade nine students should understand, on a descriptive and empirical level, experiments dealing with the inverse square law of light and emission spectroscopy. For example, they should be able to interpret flame test results to identify common elements.


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