Six Ways to See the Transit of Venus
1 As suggested in the safety guidelines above, the use of eclipse shades or of #14 shade welding glass will permit a large number of people who do not have specialized equipment to observe this event. However, as the planet approaches the limb of the sun, subtleties like the "black drop" effect will not be discernible. At one minute of arc in size, Venus is near the visual limit of most people's eyes. It's tiny compared to the sun, which is about 32 arcminutes in diameter.
Eclipse Shades or Solar Shades appear similar to sunglasses, but they have a special filter that permits safe viewing if the filter is in new condition. Eclipse/solar shades are available through Rainbow Symphony and other retailers listed at http://www.mreclipse.com/Totality/TotalityApC.html under "Solar Filters." Before looking at the sun, inspect the material to make sure the lenses are not scratched or compromised in any way. If so, discard the shades.
2 Pinhole projectors are a safe, indirect viewing technique for observing an image of the sun. While popular for viewing solar eclipses, pinhole projectors suffer from the same shortcomings as unmagnified views when Venus approaches the edges of the sun. Small features like the 'black drop' effect will not be discernible.
Dr. Hugh Hunt demonstrates a successful pinhole projection (right) of the 2004 transit of Venus at http://www2.eng.cam.ac.uk/~hemh/transit.htm. Additional instructions for pinhole projectors are at http://www.exploratorium.edu/eclipse/how.html; from the Exploratorium.
3 You may project a magnified view of the sun through a reflector telescope or binoculars onto a white surface, which conveniently allows a larger number of people to watch concurrently. See http://casa.colorado.edu/~dduncan/wp/?page_id=261 for video instructions for projecting the sun, by Dr. Doug Duncan.
The projection technique sometimes has its own limitations. Because magnified projections usually have an exposed focal point beyond the eyepiece, a bystander can inadvertently put her eye or body in the sight line of the sun. Hence, a projecting telescope must not be left unattended. (See Unattended Equipment Hazards, left column.) Large reflector telescopes can generate too much heat by concentrating a lot of the sun's energy on the secondary mirror and eyepiece, so the incoming light must be attenuated first. "Stop down" the aperture. Likewise, SCT or Schmidt-Cassegrain telescopes can experience too much heat build-up as the light bounces internally.
Hubert van Hecke provides the design and instructions for making his sunspotter. Additional pages at his Ask Mr. Science web page indicate how to take sunspot data and analyze them.
The Exploratorium demonstrates how to view a planet in transit safely by projecting the image of the sun with binoculars. Important: Do not look at the sun through binoculars without solar filters on the large ends of both the barrels. Do not leave this rig unattended.
4 A method for allowing a large crowd to witness the transit of Venus concurrently is to project a magnified image through a closed-loop device.
A popular projection device used during the 2004 transit of Venus was the now-improved Sun Funnel. Made from simple materials (a plastic funnel, a clamp, an eyepiece, and some projection fabric), the device fits in your telescope like an eyepiece with an appendage. A clear image of Venus transiting the sun appears on the screen. Because the entire light path is enclosed, observers are not at risk. A larger version of the screen uses a bucket to yield a larger image. Download simple instructions and supplies list written by AAS Press Officer Richard Tresch Fienberg.
Bruce Hegerberg's design for a Sun Gun is online at www.sunguntelescope.com.
Another viewing tool is Gene Zajac’s modified version of a Sun Gun (see 1999 GLPA Proceedings). The device safely allows a crowd of spectators to view a large projection of the sun, the transiting planet, and sunspots.
TIP: To avoid excessive heat build-up on your eyepiece, do not aim the telescope continuously at the sun for an extended time. For large scopes, stop down or attenuate the incoming light, for the telescope's purpose is to magnify the image of the sun, not to gather a lot of sunlight.
The Sunspotter is commercially available from Science First. It provides a surface on which you can safely trace the sun's outline and sunspots onto a piece of paper.
TheVenuscope and solar shades are commercially available from SODAP-SOBOMEX- Department Sky & Space.
A Solarscope is commercially available from [Light Tec Optical Instruments]
The transit of Venus is perhaps best when viewed directly when magnified, which demands an appropriate solar filter over the large end of the telescope. Often made of glass or Mylar, these "white light" filters block about 99.99% of the incoming sunlight, which allows the eyepiece then to magnify the image. A filtered, magnified view will show the sun (either blue or orange), the planet Venus, the "black drop" effect, and sunspots. See Solar Filters or http://skyandtelescope.com/observing/objects/sun/article_101_1.asp for a list of retailers.
Note #1: The sun's immense energy must be drastically reduced before it enters the telescope. Do not use small filters that fit over the eyepiece (as found in some older, cheaper telescopes), for the concentrated sunlight can shatter them.
Note #2: Remove unfiltered finder scopes so they are not inadvertently accessed. Do not rely on a lens cap--even if it is taped on--to keep the eyes of a prying person at bay. (See Unattended Equipment Hazards in left column.)
Special telescopes with built-in hydrogen-alpha filters show additional solar features, such as the sun's surface granulation and prominences extending outward into space. Though more expensive than traditional telescopes, they offer wonderful views of the magnified sun not seen by astronomers in previous centuries.
6 Transit not visible from your location, or clouds interfering? Watch the live webcast from atop Mauna Kea in Hawaii, with expert commentary brought to you by the fun team at NASA EDGE. Don't miss the 2012 transit of Venus!