How do Planets, or other objects move around a star? The observations of the German astronomer, Johannes Kepler (27 December 1571 – 15 November 1630), deduced the three laws that are being used today to answer that question. I will describe the three laws in three different lessons, starting today with the first one below.
First law. All planets describe an elliptical trajectory around the Sun (star), while the Sun is placed in one of the focus of the ellipse. Contrary to the circle that has one center point, the ellipse has to points that characterize it; those points are called each a “focus” (plural foci). Therefore the ellipse looks more like an oval, and not like a circle. If you want to know more of the ellipse, click in the link below.
Qualitative definition of the ellipse: https://www.showme.com/sh?h=nfW03O4
Quantitative description of the ellipse: http://www.showme.com/sh?h=Mt9Z97I
AstroDidactics 