English to Arabic Science Astronomy & Space

Usually in a basic class in astronomy we get taught that our planets revolve in elliptical. paths around our sun. This is not quite what you observe when using a telescope yourself, since your point of observation is fixed on the earth which itself revolves around the sun. So the planet's path actually become quite complicated curves with forward and backward motion, they are ellipses around positions on another ellipse. Historically this geocentric view formed the basis of the Ptolemaic system. Mathematically the whole family of curves of circles around points on the circumference of another circle is referred to as "epitrochoids". In the applet shown below a planet of our solar system can be chosen, and its trajectory at the sky as seen from the earth is sketched. For example if you choose "sun" as the graph generating celestial body, a perfect ellipse is drawn. Due to the very small excentricity. of the earths orbit around the sun, the ellipse is hardly distinguishable from a circle. This figure is exactly the same in the well known heliocentric perspective, only the role of sun and earth are switched. Every other planet will move in ellipses around this line of the sun in the geocentric perspective.