logo Museo Galileo - Institute and Museum of the History of Science
Observing with Galileo's Telescope

4.1 - Replicating Galileo's Observations

The Moon seen through an optical replica of Galileo's telescope Saturn seen through the optical replica

Thanks to the development of an optical instrument faithful to the original telescope, but also able to support devices for recording the images, it has been possible to launch a campaign of observations of the same heavenly bodies investigated by Galileo. The optical instrument has been produced by the Arcetri Astrophysics Observatory with replicas of the original lenses constructed on the basis of analyses conducted by the National Institute of Applied Optics. To record the images, a Charge Coupled Device (CCD), the electronic device that constitutes the heart of digital cameras today, has been used.

The first observations, of the Moon and Saturn, are significant in illustrating the main optical problem of Galileo’s telescope. The instrument’s resolving power- that is, its ability to let the observer perceive and recognise minute details in the image of a celestial body - is severely limited by the effect of so-called chromatic aberration. This phenomenon appears at a glance as a fringe of red or blue colour surrounding the heavenly bodies observed; but, more generally, it causes blurring that worsens the definition of a telescopic image.

 ŠIMSS 2008 P.zza dei Giudici 1 50122 Florence P.I. 01346820481