In astronomy, the parabola features in both the construction of telescopes and in the motion of comets around the Sun. A parabola is one of the four conic sections – a plane intersecting a cone parallel to one edge traces out a parabola. 

A parabola has the functional form:  
y = A x^{2}  

where A is the constant of proportionality. 
Parabolas in Telescope Design

The parabola is the exact shape required to focus a plane wave to a single point. Hence parabolic dishes coherently (i.e. in phase) add electromagnetic radiation at a point and are central to many telescope designs in both the optical and radio. For a parabola of equation y = A x^{2}, the point of focus lies at ( x = 0, y = A/4). 
Parabolas in Nature
Curiously a comet falling from a great distance towards the Sun will trace out a parabolic orbit with the Sun at the focus of the parabola. This is just a consequence of Newton’s laws of motion and gravitation. Similarly a projectile on Earth follows a parabolic arc as it falls under gravity.
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