This material (including images) is copyrighted!. See my copyright notice for fair use practices.
Observations of the stars in all regions of the electromagnetic spectrum and careful observations of the Sun's pulsation modes and neutrinos provide the data needed to construct models of the interiors of stars. This section is about how to find out what the interior of a star is like without physically taking one apart (a rather difficult thing to do).
Mathematical Models
Astronomers construct mathematical models of the interior of a star using the information pouring from the surfaces of stars (especially the Sun) and their knowledge of how gases behave under different conditions. The mathematical models are a set of equations that describe how things work layer by layer in a star. Fortunately, the interior of stars is completely gaseous all the way to the center, so the equations are relatively simple (whew!). The physics of gases can be described with just three parameters:
Temperature---a measure of the random motion energy (the average kinetic energy) of the gas particles. The higher the temperature, the more random kinetic energy is present.
Pressure---the amount of force/area. Hot gas expands to create pressure on its surroundings. For example, the gas inside a hot air balloon pushes out on the material of the balloon enclosing the gas.
Mass Density---the amount of mass/volume. Gaseous material can be compressed to smaller volumes and higher densities.
Equation of State
How the three parameters work together to describe the material you are studying is determined by the equation of state of the material. This is an equation that relates density, pressure, and temperature. The equation of state for solids and liquids is very complex and uncertain. The equation of state for the gas is simple: the pressure = (a constant × the mass density × the temperature) / (the molecular weight of the gas). The molecular weight of a particular type of gas is the combined mass of all of the isotopes of that type of gas in the proportions found in nature. For hydrogen, the molecular weight is very close to 1; for helium, the molecular weight is very close to 4. For a gas made of different types of atoms (such as that found in stars), the molecular weight is the weighted mean of the different atomic types, taking into account the relative proportions of the different types of atoms. This equation of state for simple gases is also called the ideal gas law.
This material (including images) is copyrighted!. See my copyright notice for fair use practices.Observations of the stars in all regions of the electromagnetic spectrum and careful observations of the Sun's pulsation modes and neutrinos provide the data needed to construct models of the interiors of stars. This section is about how to find out what the interior of a star is like without physically taking one apart (a rather difficult thing to do).Mathematical ModelsAstronomers construct mathematical models of the interior of a star using the information pouring from the surfaces of stars (especially the Sun) and their knowledge of how gases behave under different conditions. The mathematical models are a set of equations that describe how things work layer by layer in a star. Fortunately, the interior of stars is completely gaseous all the way to the center, so the equations are relatively simple (whew!). The physics of gases can be described with just three parameters:Temperature---a measure of the random motion energy (the average kinetic energy) of the gas particles. The higher the temperature, the more random kinetic energy is present.Pressure---the amount of force/area. Hot gas expands to create pressure on its surroundings. For example, the gas inside a hot air balloon pushes out on the material of the balloon enclosing the gas.Mass Density---the amount of mass/volume. Gaseous material can be compressed to smaller volumes and higher densities.Equation of StateHow the three parameters work together to describe the material you are studying is determined by the equation of state of the material. This is an equation that relates density, pressure, and temperature. The equation of state for solids and liquids is very complex and uncertain. The equation of state for the gas is simple: the pressure = (a constant × the mass density × the temperature) / (the molecular weight of the gas). The molecular weight of a particular type of gas is the combined mass of all of the isotopes of that type of gas in the proportions found in nature. For hydrogen, the molecular weight is very close to 1; for helium, the molecular weight is very close to 4. For a gas made of different types of atoms (such as that found in stars), the molecular weight is the weighted mean of the different atomic types, taking into account the relative proportions of the different types of atoms. This equation of state for simple gases is also called the ideal gas law.
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