Arecibo telescope is made up of a mosaic of nearly 40,000 aluminum
panels with an overall bowl shape that is 305 meters (1,000 feet)
in diameter. Imagine that the shape of the aluminum bowl is aligned
in such a way that all the panels, of which it is made, keep it
precisely spherical in shape to within about 1.5 millimeters (about
the width of the lead in a pencil). This is the mechanical engineering
achievement that the telescope represents.
Arecibo Obervatory: A Timeline