Helioscope

Already in 1610 Thomas Harriot made the first telescopic observations of sunspots, which were published in 1611.  Harriot's observations of the Sun, made directly through the telescope, risked permanently damaging the observer's eyes.  In order to allow safe observation, the telescope was repurposed as a 'helioscope', through which an image of the Sun was projected onto a sheet of paper, where it could be transcribed for later study.

Invented by Benedetto Castelli (1578 – 1643) and subsequently developed by his teacher, Galileo, the helioscope was perfected during the early seventeenth century particularly by Galileo's opponent in a bitter controversy on the nature of sunspots, the Jesuit astronomer Christoph Scheiner (1575-1650). A brief video provided by the Museo Galileo recounts both the invention of the helioscope by Castelli and its further development by Galileo and Scheiner. These images are taken from Scheiner’s culminating contribution to the subject. The second image represents the most advanced form of the instruments he created.

Images. Christoph Scheiner, Rosa Ursina, sive Sol ex admirando facularum et macularum suarum phoenomenon varius (Bracciano: printing began in 1626 and finished in 1630), pp. 150 and 353 resp. Source: Wikimedia (public domain): here and here. The full work can be consulted on the digital library of the Museo Galileo.

Related resources. For another aspect of Jesuit work in astronomy, see the online exhibition at the History of Science Museum, Oxford: Heaven on Earth: Missionaries and the Mathematical Arts in 17th-Century Beijing.