Hello Anselmo, Venus has already transited and therefore the problem is only theoretical, even if the same considerations are valid also for observing the sunspots.
A shadow sharpener is completely useless to observe Venus on the Sun or a sunspot. It is useful only to project on a plane (as in a dark room) a near object illuminated from behind by the Sun. For example to show the edge of a gnomon and to see where exactly its shadow (or its penumbra) begins. In the case of Venus the black disk (Venus) is too far from us and it is in practice part of the source (Sun). For better explanations you can read the articles of William Walton and mine published on The Compendium #9-4 , December 2002 . A welding glass is enough safe to filter the light of the sun (and particularly the ultraviolet rays) but it has poor optic properties and therefore it deforms the image and prevents the vision of thin details on it. Some friends and I , on 8th June, have seen clearly the disk of Venus on the Sun using a solar filter (naked eye), but we have not succeeded in seeing it using a welding glass. Regards Gianni Ferrari 44° 39' N 10° 55' E Mailto : [EMAIL PROTECTED] ----- Original Message ----- From: "Anselmo Perez Serrada" <[EMAIL PROTECTED]> To: <[email protected]> Sent: Tuesday, May 11, 2004 11:51 PM Subject: More on Venus Transit > Hi, > > This question goes to the shadow-sharpeners experts: > > Which is better (or worst) to observe the transit of Venus, > a shadow-sharpener or a welding glass? Or both are more > or less equally bad? > > Regards, > > Anselmo > > > > - > -
