Electromagnetic Spectrum/Kepler/Motion Flashcards
_____________ and helium, the most abundant elements in stars in the solar neighborhood, are also the most abundant constituents of the stars in all kinds of clusters.
Hydrogen. Open clusters have a comparable element content to that of the sun. However, globular clusters have a much lower element content. Differences in chemical composition are related to differences in stellar population.
The ________ and the vast majority of other stars are stable and in a steady state, neither expanding nor contracting.
Sun. This state of stability is called a condition of equilibrium. All the forces within it are balanced so that at each point within the star, the temperature, pressure, density, etc. are maintained at constant values.
A balance between the weights of various layers and the pressures that support them is called ______________ equilibrium.
Hydrostatic. This shows that the surface and internal temperatures of stable stars is balanced. If the internal gas pressure in a star were not great enough to balance the weight of its outer parts, the star would collapse and contract until the gas pressure inside built up to the point where it could support the star.
The ____________ gas law provides a mathematical relation between the pressure, density, and temperature of an ideal gas and states that the pressure is proportional to the product of the density and temperature of the gas.
Perfect. The gases in most stars closely approximate an ideal gas and must obey this law. The pressure is proportional to the density and temperature of the gas.
Energy associated with the motion of the molecules in a star is called stellar _____________ energy
Thermal. The thermal energy of a star is the internal heat. The heat stored in a gas is simply the energy of the motion of the particles that comprise it.
Energy that can be released by the collapse of a system is called ______________ energy.
Gravitational. Because a star is bound together by gravity, it has gravitational potential energy, as does a star cluster. If the various parts of a star fall closer together, it converts part of its potential energy into heat, some of which can be radiated away.
Because of its enormous mass, the sun need contract only extremely slowly to release enough gravitational potential energy to account for its present luminosity.
In the ______________ approach to the study of stellar evolution, calculations are made from the theory of stellar structure about how stars should change as they contract gravitationally or age through changes in their chemical composition produced by nuclear reactions.
Theoretical. A typical lifetime for a star might be something like ten billion years. The study of the changes and expected changes is then theoretical and based on speculation.
In the ________________ approach, stars or groups of stars are observed that are at different stages in their evolution and it is determined whether they actually exhibit the characteristics expected of them from the theoretical predictions.
Observational. The difficulty in the observational approach is that a star ages extremely slowly by human standards and except for those brief periods in its existence where it may be variable or explosive, we do not actually “see” a star evolving.
A __________ ________ is a star that has exhausted most or all of its nuclear fuel and has collapsed to a very small size and it believed to be a star near its final stage of evolution.
White dwarf. The predicted mean density of these stars range from about fifty thousand to over one million times that of water. At such densities, matter cannot exist in its usual state. Although it is still gaseous, its atoms are completely stripped of their electrons and the latter are obliged to move according to certain restrictive laws. The matter in white dwarfs is said to be degenerate and this category–approximately ten percent of all stars–are believed to be in the final state of stellar evolution.
The ________ ______________ is a sequence of stars on the Hertzsprung-Russell diagram (H-R diagram) containing the majority of stars and they run diagonally from the upper left to the lower right.
Main Sequence. The main sequence is the locus of points on the H-R diagram representing stars of similar chemical composition but different mass. The majority of stars are aligned along this section, approximately ninety percent.
About 23,000 stars are plotted on the Hertzsprung-Russell diagram to show the relationship between absolute magnitude, luminosity, classification, and the effective temperature of the stars. This diagram shows that stars tend to fall only into certain regions on the diagram.
A _____________ is a star of large luminosity and radius.
Giant. A super giant is a star of very high luminosity. Less than one percent of the stars shown on the H-R diagram are believed to be classified as giant or super giant.
Astrophysicists typically indicate a star’s luminosity by its ___________ ______________, which is the brightness of a star as seen from a distance of 10 parsecs, or 33 light years.
Absolute Magnitude. This is different from apparent magnitude, which is a star’s brightness as seen from Earth.
The oldest assemblages of stars in the galaxy are believed to be the _____________ clusters.
Globular. Ages for globular clusters are now variously estimated at anywhere from ten to twelve billion years old. Globular clusters are composed of population II stars.
The fragmentation and vaporization of a meteorite upon entering the atmosphere is called _____________.
Ablation. As a meteoroid plunges into the Earth’s atmosphere at a speed of many miles per second, it undergoes many collisions with air molecules. The impinging molecules penetrate the meteoroid and chip off pieces of it. The surface of the meteoroid heats up and the dislodged particles vaporize.
The fraction of incident light that is reflected by a body is called its ____________.
Albedo. The moon’s albedo is about 0.07, which means that it reflects only about 7% of the light from the sun. It absorbs most of the sunlight.
Visible light is the range of electromagnetic ______________ that is detectable by the human eye.
Radiation. Radiation is a general term for energy emitted as particles or waves;
Optical astronomers use optical telescopes, such as the refracting and reflecting telescopes you learned about, to study stars based on the visible light they emit. In the 1930s, another approach to “observing” the stars was discovered, using __________ telescopes.
Radio. The sun and most stars release most of their radiation in the visible light spectrum. However, some objects actually emit a lot more radiation at the radio wavelengths than at those of visible light. Therefore, while they might be too dim to detect with optical telescopes, they’re very “bright” when seen with a radio telescope.
