This Day in History

 

Painting by Giuseppe Bertini

On this day in 1609, Galileo began observing the moon with his telescope.

Dutch eyeglass makers had invented the telescope in 1608, but Galileo improved upon it greatly.  He ground and polished his own lenses for greater magnification.

He found that the surface of the Moon was not smooth, but full of mountains and valleys like Earth.  He was the first to publish a detailed report of his findings in 1610, called Starry Messenger (Sidereus Nuncias).

Galileo's drawing:

Of course, the Roman Catholic Church had adopted Aristotle's beliefs that the heavenly bodies were perfect and the Earth was at the center, which is why Galileo was forced to recant in 1633 and remained on house arrest until his death in 1642.

You may recall I previously shared a photo of Galileo's lens, on display in Florence. It is adorned with a frame commissioned by the Medici in 1677, designed by Vittorio Crosten.

The Galilean telescope used a convergent objective lens and a divergent eyepiece lens.  Because the design has no intermediary focus, it results in a non-inverted image.  He had to use aperture stops to reduce the diameter of the objective lens to limit aberrations.