Thursday, 4 January 2018

Ganymede and Callisto

On Jan 3rd there was another clear morning. I could see Jupiter and two of its moons clearly in the Tudor Telescope. However, photographing the image I could see was difficult. The image was too dark for my mobile phone camera to capture and my Canon Ixus kept focussing on other objects in the view field. I eventually tried a manual live setting and got the image below which I cleaned up using Lunapics.
From the shallow sky website I found the positions of Jupiter's Moons and got a good match for Callisto and Ganymede.
The other two moons were too faint and I could not see them on this occasion.  The photo I took above was the best one out of about 50 so  lot of persistence was needed to get a good result.  Of course I knew what I was looking for but with the Tudor Telescope images do go awry if the mirror is not looked into at the correct angle. To a Tudor user it would have been hard to have known which was the right perspective and which was the false perspective. Even if a user of the perspective glass had looked at the Moon and seen craters they may have dismissed this as a false image which had gone awry. Thomas Digges in his mathematical work Alae seu scalae mathematicae in the section  Radij Astronomici  writes of hallucinationem Oculi (delusion eye) see for details.
Unlike the Dutch Trunke and Galileo's self made telescope the Tudor Telescope does not work well when used with a quadrant or staff for measuring accurate positions of the stars and planets.  When Galileo demonstrated his telescope to the Doge in Venice he focussed it on a tower in nearby Padua which would have been well known to the Doge so he would be familiar with the image the telescope produced.  Galileo had sufficient confidence in his telescope and his observations to write about the lunar features he saw as well as the Jovian moons and the phases of Venus.  Galileo's Sidereus Nuncius is  model of scientific reporting and accuracy and the images he saw did not give a false perspective if he looked through his telescope awry with the wrong angle.  All the same I think the image above of Jupiter and two of its moons is remarkable for  home made telescope based on a model from the sixteenth century when Queen Elizabeth I sat on the English throne. 

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