Contents

• Introduction
• Space Exploration and Solar System
• Stars and Nebulae
• Milky Way
• Galaxies
• more Astrophysics
• Observations/Instruments
• other Stuff
• Numerical Maths
• Radio and Electronics
• my Home Page
• Other Material for Teaching Astronomy

Most of the applets are done with the JDK 1.05 only (and thus work also on Netscape3), but some are JDK 1.2.

Space Exploration and Solar System

• The PassFinder applet gives prediction of satellite passes over a ground station. For a period of days, following either the current time or any user-specified time, it computes the Equator Crossings, the start and end times of a pass, the azimuts at start and end, the maximum elevation, the minimum range, as well as the expected maximum signal strength of the satellite's transmitter with specified EIRP. At the present time, I include only a few satellites that are of some personal interest, but I hope that I will be able to include more satellites...
  This applet is an adaptation of the Java program PassFinder by P.J.Fernandez
• The Orrery applet permits to view the Sun, the Moon, any planet, or any moon of any planet and a small portion of sky around it, for any time and date, and as seen from various places on Earth. Apart from a rendering of that heavenly body, all data on its position in the sky, rising and setting times, distances from Earth and Sun, and other information can be obtained. The progress of lunar and solar eclipses can be displayed, as well as the transits across the face of the Sun of the inner planets Mercury and Venus. Also, occultations of the planets by the Moon can be inspected. This applet was written by Sébastien Poirier in summer 1999 during an internship. (notes: there is still a slight problem in the orientation of the shadows of the Moon and the planets ... the amount of shadowing is correct!
  Also, there are no explanation pages yet ... i am still adding features ;-)
• Simulation of the Flight of a Launch Vehicle allows the computation of the behaviour of a multistage rocket from the launch site into orbit. The user may change the parameters of the rocket, such as the type and mass of the fuel, the thrust of the engines, the satellite weight, the orientation of the thrust vector during the powered flight etc. One can study the characteristics of the ascent trajectory and the achieved orbit. This is an applet designed and programmed by Guillaume Gouge, Sébastien Majerowicz, Sébastien Poirier, and Vincent Prud'homme in winter 1999 as a second-year project of the ENSPS school of physics.

• Two Body Simulation shows the movement of a body in the attractive field of another body, e.g. a planet around the Sun. This is the simple Kepler problem, but done for a general attractive force. Also, one of several different numerical methods can be used (Old version).
• Two Body Simulation (NEW) shows the movement of a body in the attractive field of another body, e.g. a planet around the Sun. This is the simple Kepler problem, but done for a general attractive force. Also, one of several different numerical methods can be used. This new version allows to make time plots of the distance to the central body, the speed, and the kinetic and potential energy as well as their sum (help pages t.b.d.)
• Three Body Simulation subjects a small satellite to the combined gravitational pull from both Earth and Moon as they circle each other. Kepler's laws no longer hold true for the satellite, because of the perturbations by the Moon. Changing the mass ratio of Moon/Earth permits also to simulate a planet moving around a binary star.
• Three Stars' Ballet For three stars of equal mass, there are known a couple of stable configurations, where the three masses will orbit each other always in the same way. Euler's and Lagrange's solution have been known for a long time, while the Figure-of-8 configuration had been found only a few years ago. The applet permits to display the orbits, as well as to study the stability of the configuration, by allowing to perturb the initial positions and velocities as well as the masses from their ideal values. (Help Page is to be done ...)
• Saturn's Ring is a simulation of how the orbits of dust particles around a planet are perturbed by the presence of a moon.
• Stability of Saturn's Ring: In 1865, in his Essay which won him the Adams Prize, J.C.Maxwell showed - among other things - that a ring of moons in circular orbit around Saturn could be stable, if the number of satellites does not exceed a number which depends on the mass ratio of the ring and the planet. At this site, I collect several applets which demonstrate various aspects of Maxwell's study, including a full n-body simulation of the problem. (this site is under development - dec. 2008)
• Lagrangian Points are equilibrium points for a satellite in the gravitational field of two large masses which orbit each other. This applet gives a graphical representation of the effective potential for the satellite, as seen by an observer who rotates with the orbiting primary masses. It allows to inspect this potential, to locate the Lagrangian points, and investigate their neighbourhood. (Help Page still under development)

• EarthShooter simulates the collision of an asteroid with the Earth, in a simple two-body treatment. It shows the effects of "gravitational focussing", and that for small approach speeds the Earth presents a larger effective cross section than its geometric cross section.
• NEO Simulator allows to study the effect of exploding an asteroid or trying to deflect it in order to avoid collision of the asteroid with Earth. This takes place in the gravitational sphere of influence of the Earth, and addresses what could be done in the very last moments.
• Comet Halley's Orbit in the Solar System is an application of the wonderful Applet OrbitViewer by O.Ajiki and R.Baalke to the comet Halley. It allows to view the positions of the planets at any time and to view their orbits from any angle.
• The Michelin Guide to the Solar System is an extension of the above applet, which permits to find the launch windows for interplanetary missions: If you want to plan your next holidays on Mars, or travel to Saturn for a close-up view of the rings, you need to know when there are possible times to start on such a trip, and how costly it will be in terms of rocket fuel. This is the aim of this applet developped by Isabelle Edmond, Pauline Ginestet, Vivien Raymond, and Matthieu Rieser in spring 2007 as their second-year project of the ENSPS school of physics.
• The Michelin Guide to the Solar System: Slingshots is a further extension of the above Michelin Guide. It also allows to compute the gravity assist maneuvers, by which the space ship passes closely by a planet and thus its trajectory is strongly altered, which permits to arrive at a farther planet with no extra fuel. This applet was developped by Sarah Lawday, Jérémy Lebreton, Axel Richard, and Florence Gris in winter and spring 2008 as their second-year project of the ENSPS school of physics. (some alterations and additions are scheduled)
• Travels in the Solar System uses Keplerian orbits to show how a body travels through the Solar System. Such a body may either be a comet or asteroid headed for a collision with Earth or a spaceship which we launch towards the planets. One can view the travel times or the warning times before the collision, and estimates for the effects of the impact such as crater size, are given.
• PlanetTraveller is an extension of Travels in the Solar System. It uses Keplerian orbits to compute the time windows available for travelling from the Earth to another body orbiting the Sun, such as a planet, asteroid, or comet. For these mission windows, it displays the various properties of the mission, such as departure and arrival speeds, orbital eccentricity and period. It thus allows to optimize an interplanetary space mission.
• Fly To Jupiter is a version of the above applet.

• Decision map displays on a map of NEO diametre and the speed at its impact on Earth various data: the energy of the impact (to judge how severe the consequences of such an event would be). Then the time before collison at which the body could be detected, given a limiting visual magnitude. And the energy that would be required to cause a given deflection of the trajectory, depending on the time of launch and the speed of an interceptor. All calculations are done in a rather rough approximation, that the NEO approaches on a straight line at constant speed. This neglect of the effects of gravity by the Earth and by the Sun limits such a study to fast objects, but one can still get a rather good impression about the principal issues. (Help Page still under development)

• SpaceMirrors studies whether it is possible to heat the waters of an atoll by the sunlight reflected from mirrors in Earth orbit, for example to generate electricity. The simulation permits to compute the solar flux reflected to the atoll as a function of time, for any number of mirrors placed in orbit at any height; it computes the average irradiation, compared to the direct sunlight, and with a simple model for the heat losses estimates the evolution of the water temperature. This applet is a further developed version of the designed and programmed by Baptiste Rouillier, Amandine Fallet, Stéphane Hau, and Mounir El-Mendili in 2005/06 as their second-year project of the ENSPS school of physics.
• The compute positions of Sun and Moon for any time and location by Jürgen Giesen
• The Daylight applet for any time and location by Jürgen Giesen
• The TV satellite position computer 1 (in English)
• The TV satellite position computer 2 (in French)
• The TV satellite position computer 3 (in French)

Stars and Nebulae

• The formation of an Absorption Line in a stellar atmosphere is computed for a simple case. One can study how the shape of the line changes if one alters the line opacity and the radial velocity as a function of depth in the atmosphere (I still must do the explanations.....)
• The formation of an Blended Absorption Line considers a line which is situated near another, strong line. One can study how the shape of the line changes if one alters the parameters of the blending line and the opacity and radial velocity of the line of interest (I still must do the explanations.....)
• Interstellar Extinction is a small utility that allows the conversion of extinction, optical depth, attenuation for any optical, ultraviolet and infrared wavelength, using the standard interstellar extinction curve.
• Compute the radius of the Strömgren Sphere around a source of ionizing radiation, given the number of ionizing photons.
• Analysis of an emission nebula as a Strömgren Sphere assumes a simple model to estimate the distanace of the object from its observed Hbeta flux, angular diametre, and electron density. Also, we get the number of ionizing photons necessary to make the nebula, and the luminosity of the central star.
• Plasma Diagnostics interprets the emission line spectrum of ionized gaseous nebulae: from the observed intensities of the lines, temperature, density, and the abundances of the elements in the nebula are derived. Also, given these values, the expected line intensities are synthesized. This is a scaled-down version of my professional-level code HOPPLA.
• Plasma Diagnostics (version3) also permits to show the results obtained by a number of analysis methods based on the strong lines only.
• Plasma Diagnostics of IR lines is similar to the applet above, but deals with the infrared lines: for given values of extinction constant, and the temperature and density of the electrons, the abundances of the elements in the nebula are derived from the observed line intensities.
• The Spectrum of a single Ionic Species computes the intensities of major emission lines, if you specify the observed intensity of one of the lines. Helps you to check whether you have indeed got all the lines of this ion that you should have been able to observe.
• Stellar Evolution shows the computed evolutionary paths of any star between 0.8 and 120 solar masses in the Hertzsprung-Russell diagram, as well as the isochrones, i.e. the locus of stars of any given age (NEW version, but old Help pages ....)
• The Light curves of eclipsing binary star by Terry Herter at Cornell University.
• The Orbits of a binary star by Terry Herter at Cornell University.
• The Orbits of a binary star my own version ...