posted by: bueter
One of the best ways for a group of people to view the magnified sun safely is to use a rear screen projection that is enclosed. Because no one is exposed to the intense light path, an Sun Funnel allows a crowd of people to see concurrently the transit of Venus, sunspots, or eclipses.
Last week I co-presented a make-and-take workshop to build the inexpensive telescope accessories at the ASP meeting in Baltimore. You can readily make one yourself, for AAS Press Officer Richard Tresch Fienberg wrote and illustrated Build a Sun Funnel for Group Viewing of Sunspots and the Transit of Venus. The how-to manual gives clear, step-by-step assembly instructions and sources for inexpensive materials.
Another hands-on workshop to build Sun Funnels will be at the Great Lakes Planetarium Association (GLPA) 2011 Annual Conference in Champaign, IL, on October 20, 2011. Several GLPA members successfully used Sun Funnels to witness the 2004 transit of Venus. I still use mine to look at sunspots, too.
See Eye Safety for more techniques and advice for viewing the sun safely.