The Astrophysics Spectator



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Interactive Pages

Index of Simulator Pages

The simulator pages on this web site illustrate basic processes at work in astrophysics. Each simulator page fully describes the design and use of an embedded simulator. All simulators are Java applets, and their use requires a Java-enabled browser. Every simulator page on this web site is listed on the current page.

Each simulator page is part of an astrophysics survey path, and will normally be encountered by the reader as he follows that path. A simulator page on a survey path plays the same role that plots and figures play in a book. It is not a self-contained page; rather, it is an integral part of its survey path.

All simulators can be controlled with either the mouse or the keyboard. All simulators conform to a common set of mouse and keyboard commands. These are described on the Applet Control Guide page.


Special Relativity

The Keplerian Orbit Simulator. This simulator page presents the orbits of the five inner planets around the Sun. The simulation is based on Newtonian gravity under the assumption that the mass of a planet is negligible. The simulator provides three initial states: the planets have the parameters of Mercury, Venus, Earth, Mars, and Jupiter; the planets all have the same semimajor axis but different eccentricities; and the planets have semimajor axes that produce resonant periods. The reader can freely reset these parameters. The Keplerian Orbit Simulator is part of the “Gravitational Physics” survey path. (continue)

The Galactic Disk Orbit Simulator. The Galactic Disk simulator shows the orbits of stars in the plane of a galaxy with a gravitational field characteristic of spiral galaxies. The simulator provides four sets of orbital parameters; each set is intended to display a particular characteristic of the stellar orbits. The reader is free to set the orbital parameters for each star in the simulation. The gravitational field model is of a homogeneous core and a constant velocity plane. This simulator page is part of the “Gravitational Physics” survey path. (continue)

Constant Acceleration Simulator. The free-fall motion of bodies relative to a traveler accelerating at a constant rate is the same as that of bodies near a black hole. With the Constant Acceleration Simulator, the reader can experiment with the motion of objects in an accelerated reference frame. The simulator shows the motion of objects both as measured in a Cartesian coordinate system and as seen by the accelerating traveler, demonstrating the effects of time dilation and of light propagation close to the traveler's event horizon. This simulator is part of the “Special Relativity” survey path. (continue)

General Relativity

Point Gravitational Lens Simulator. This simulator shows how the gravitational lens of a star distorts the image of more distant objects. The simulator shows two figures: a figure of the position of the lens and the object behind the lens, and a figure of the image created by the lens. The reader can drag the lens with his mouse pointer to a new position. This simulator is part of the “General Relativity” survey path. (continue)

Schwarzschild Lens Simulator. This simulator shows the effect of a Schwarzschild black hole on the appearance of the sky. The black hole acts like a crystal, creating an infinitude of images of the whole sky that lie on annuli encircling the black hole. The simulator permits the reader to rotate the sky relative to the black hole. The black hole has its strongest effect on starlight when a star is directly behind it; the surface area of the star's image is very large, wrapping completely around the black hole. A star behind the observer also has an image that wraps around the black hole, but the image's width on the sky is very narrow. While the simulator calculates the four largest images that the black hole creates of a source, only two are generally visible. (continue)



The PP Hydrogen Fusion Simulator. The PP hydrogen fusion simulator calculates the evolution of a gas undergoing thermonuclear fusion through the proton-proton fusion processes. The simulator evolves the gas over 1 trillion years for a gas of constant temperature and with a constant density of nucleons. The results are presented as a log-log plot in time starting at 1/100th of a year and ending at 1012 years. The reader can choose one of three plots: a plot of composition, a plot of power generation, or a plot of the relative contribution of various fusion processes to the production and destruction of helium. The temperature can be set to values between 5 and 50 million degrees Kelvin, and the relative abundances of hydrogen and helium-4 can be adjusted. (continue)

The CNO Hydrogen Fusion Simulator. In our epoch, massive main-sequence stars convert hydrogen to helium through the carbon-nitrogen-oxygen processes. The CNO Hydrogen Fusion Simulator simulates the complete conversion of hydrogen into helium over time through these processes. The reader can adjust the temperature and composition of the gas in the simulation. The simulator calculates the composition, power, and relative contribution of each CNO cycle to the helium production as functions of time. (continue)

The Hydrogen Fusion Simulator. Main sequence stars of our epoch convert hydrogen into helium through either the processes of the proton-proton (PP) chains or of the carbon-nitrogen-oxygen (CNO) cycles. Which of these two sets of processes is dominant in a gas depends on the temperature and composition of the gas. The hydrogen fusion simulator incorporates all of the PP and CNO processes, allowing the reader to experiment with the effects of temperature and composition on the generation of thermal and neutrino energy and on the time for the full conversion of hydrogen into helium-4. (continue)

The Helium Fusion Simulator. This simulator is a Java applet that follows in time the nuclear fusion of helium into carbon, oxygen, and neon. The reader can adjust the temperature of the gas undergoing nuclear fusion. At the start of a simulation, the gas to undergo fusion is pure helium. The simulator calculates the change in composition up to the time that all of the helium is exhausted. (continue)

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