Witness a transit of Venus! This section guides observers to observe the 2012 Transit of Venus safely. Feature topics include:
- Where to Be (and When)
- Safe Viewing Techniques
- Travel and Tours
- Planning Community Transit of Venus Events
Where to Be (and When)
Whether and when you can see the 2012 transit of Venus depends on your location. Key highlights include the four "contacts" near the beginning and end of the transit when Venus appears to touch the edge of the sun. Most of North America sees the beginning of the transit in the afternoon and evening (find a clear western horizon!) on June 5, whereas much of Eurasia sees the end of the transit in the morning (find a clear eastern horizon!) on June 6.Click to access and enlarge PDF version of map showing visibility of 2012 transit of Venus. Courtesy of Fred Espenak (NASA GSFC), who provides additional transit of Venus data from NASA.
To see an animation of how the sun appears at Region X, near Iceland, see http://youtu.be/3b7a_zXMnnU.
PDF version) shows the path of Venus across the sun and the contact times from an earth-centered perspective. However, from different locations on earth, the exact contact times vary by minutes or seconds. That slight difference in times is the essence of a transit's value, for it allowed astronomers to calculate the size of the solar system. The entire event takes about 6 hours 40 minutes. The times in the diagram are in Universal Time, or essentially Greenwich Time.
For simplicity, visit http://www.transitofvenus.nl/details.html, or select a nearby city from one of the Links: Where to Be.
So, is the transit of Venus visible June 5 or June 6?
It depends on your time zone. Generally, for the Americas where it is visible (blue colors on map below) the 2012 transit occurs the evening of Tuesday, June 5, 2012. For Eurasia and Africa where it is visible (sage colors on map), the latter part of the transit is seen the morning of June 6, 2012. Map courtesy of Steven van Roode.
[Note: Some confusion may arise from published tables with a title stating the 2012 transit of Venus is on June 6. By default, these tables are titled by the mid-transit point in Universal Time. Because the middle of the transit occurs just after midnight on June 6 in Greenwich Time (even though it's not visible then in Greenwich), the title nonetheless affirms June 6. ]
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!
Viewing the Transit & Eye Safety
B. Ralph Chou, MSc, OD
Associate Professor, School of Optometry, University of Waterloo
[See also http://youtu.be/4RGr9FcBrSM for talk at 2012 Symposium at University of Toronto.]
Watching the profile of Venus as it passes across the Sun during a transit is a wonderful demonstration of the way the solar system works. Over the course of several hours, Venus traces a path across the disk of the Sun, then leaves, in what can be thought of as an extreme example of an annular eclipse of the Sun.
Observing the Sun, however, can be dangerous if the proper precautions are not taken. The solar radiation that reaches the surface of Earth ranges from ultraviolet (UV) radiation at wavelengths longer than 290 nm, to radio waves in the metre range. The tissues in the eye transmit a substantial part of the radiation between 380–400 nm to the light-sensitive retina at the back of the eye. While environmental exposure to UV radiation is known to contribute to the accelerated aging of the outer layers of the eye and the development of cataracts, the primary concern over improper viewing of the Sun during the transit is the development of “solar retinopathy” or retinal burns.
Exposure of the retina to intense visible light causes damage to its light-sensitive rod and cone cells. The light triggers a series of complex chemical reactions within the cells which damages their ability to respond to a visual stimulus, and in extreme cases, can destroy them. The result is a loss of visual function, which may be either temporary or permanent depending on the severity of the damage. When a person looks repeatedly, or for a long time, at the Sun without proper eye protection, this photochemical retinal damage may be accompanied by a thermal injury—the high level of visible and near-infrared radiation causes heating that literally cooks the exposed tissue. This thermal injury or photocoagulation destroys the rods and cones, creating a small blind area. The danger to vision is significant because photic retinal injuries occur without any feeling of pain (the retina has no pain receptors), and the visual effects do not become apparent for at least several hours after the damage is done (Pitts 1993). Viewing the Sun through binoculars, a telescope, or other optical devices without proper protective filters can result in immediate thermal retinal injury because of the high irradiance level in the magnified image.
Because the apparent diameter of Venus is only 1/30 that of the Sun, there is never a time during the transit when it is safe to look at it without proper eye protection. Failure to use proper observing methods may result in permanent eye damage and severe visual loss. This can have important adverse effects on career choices and earning potential, because it has been shown that most individuals who sustain solar retinopathy eye injuries are children and young adults (Penner and McNair 1966, Chou and Krailo 1981, and Michaelides et al. 2001).
The same techniques for observing the Sun outside of eclipses are used to view and photograph the transit (Sherrod 1981, Pasachoff 2000, Pasachoff and Covington 1993, and Reynolds and Sweetsir 1995). The safest and most inexpensive method is by projection. A pinhole or small opening is used to form an image of the Sun on a screen placed about a metre behind the opening. Binoculars or a small telescope mounted on a tripod can also be used to project a magnified image of the Sun onto a white card. All of these methods can be used to provide a safe view of the transit to a group of observers, but care must be taken to ensure that no one looks through the device. The main advantage of the projection methods is that nobody is looking directly at the Sun. The disadvantage of the pinhole method is that the screen must be placed at least a metre behind the opening to get a solar image with a silhouetted disk of Venus that is large enough to be easily seen.
The Sun can only be viewed directly when filters specially designed to protect the eyes are used. Most of these filters have a thin layer of chromium alloy or aluminum deposited on their surfaces that attenuates both visible and near-infrared radiation. A safe solar filter should transmit less than 0.003% (density ~4.5) of visible light and no more than 0.5% (density ~2.3) of the near-infrared radiation from 780–1400 nm. (In addition to the term transmittance [in percent], the energy transmission of a filter can also be described by the term density [unitless] where density, d, is the common logarithm of the reciprocal of transmittance, t, or d=log10[1/ t]. A density of ‘0’ corresponds to a transmittance of 100%; a density of ‘1’ corresponds to a transmittance of 10%; a density of ‘2’ corresponds to a transmittance of 1%, etc.). Figure 1 shows transmittance curves for a selection of safe solar filters (Chou 1981, 1998). The “safe” zones of the plot are transmittance levels less than 0.0001 between 200 and 780 nm (above the 1E-04 line in the graph) and transmittance levels less than 0.001between 780 and 1400 nm (above the 1E-03 line in the graph). The longer infrared between 1400 and 2500 nm does not get past the tears and front of the eyeball, so is not a problem.
What if it's cloudy?
If your observing site's weather may be marginal, consider traveling to the TROVE celebration near the Michigan-Indiana border. Multiple attractions will insure a memorable 2012 Transit of Venus experience. Immerse yourself in art exhibits, historical displays, planetarium programs, webcasts, public lectures, and even a Transit of Venus specialty beer! At the fourth contact we will seal a Transit of Venus Time Keg, to be opened when the next transit of Venus pair approaches in 2117 and 2125.If it's cloudy, you can still experience the transit of Venus in real time. Complement your transit of Venus experience with views and commentary that are broadcast from around the world, including a live webcast from NASA EDGE or from SLOOH. For more featured destinations, see Where to Be, or find a Sun-Earth Day Event Location through the interactive NASA map.
article notes, "Mr. Severn's very complete and skilful arrangements were unfortunately defeated by cloudy weather occurring at the time of the transit. Our readers will probably find it easier to sympathise with his disappointment than to realise his feelings on seeing the labour and preparation of years thus rendered useless by circumstances far beyond his own control. Well might he exclaim, 'L'homme propose--Dieu dispose.'"
You can still get value out of the transit of Venus experience even if clouds disappoint,
Links: Where to Be
Excellent site automatically calculates your local circumstances (time of sunrise, time of sunset, times of all four contacts, altitude of the sun, etc.), based on your Internet connection. You can easily modify your location with a provided Google map. From Steven van Roode.
World map of ingress times (contacts 1 & 2).
World map of egress times (contacts 3 & 4).
Interactive map shows NASA Sun-Earth Day Event Locations, keeping you up to date on what's happening in your neighborhood. Upload your own events here, too.
TROVE: Celebrating the Riches of the TRansit Of VEnus. The Michiana area near the Michigan-Indiana, USA, border is a hub of activity related to the transit of Venus. Join us to celebrate the math, science, and art of this celestial phenomenon.
Take an exclusive tour of transit of Venus highlights in Indiana, with lectures, art exhibits, historical artifacts on display, webcasts, telescopic sungazing, and a post-transit celebration with Venusian ale at a Michigan microbrewery.
"The global visibility of the 2012 transit is illustrated with the world map... The entire transit (all four contacts) is visible from northwestern North America, Hawaii, the western Pacific, northern Asia, Japan, Korea, eastern China, Philippines, eastern Australia, and New Zealand. The Sun sets while the transit is still in progress from most of North America, the Caribbean, and northwest South America. Similarly, the transit is already in progress at sunrise for observers in central Asia, the Middle East, Europe, and eastern Africa. No portion of the transit will be visible from Portugal or southern Spain, western Africa, and the southeastern 2/3 of South America." Courtesy of Fred Espenak.
Contact times (Universal Time) and corresponding altitudes of the Sun for 121 international cities. From Fred Espenak.
Contact times (Universal Time) and corresponding altitudes of the Sun for 60 cities in the USA. To convert to Daylight Saving Time, subtract 4 hours if you are in Eastern Time Zone; subtract 5 hours in Central Time Zone; subtract 6 hours in Mountain Time Zone; subtract 7 hours in Pacific Time Zone. From Fred Espenak.
Global map by Michael Zeiler depicts the zones of visibility for the 2012 transit of Venus.
Maps with text in dozens of other languages are also available at http://eclipse-maps.com/Eclipse-Maps/ToV_maps.html, courtesy of Michael Zeiler.
World map of visibility; General description, geocentric data, and list of ingress/egress times for major world cities (PDF). From US Naval Observatory.
Local circumstances of the 2012 transit of Venus for observers in the United Kingdom. From HM Nautical Almanac Office.
Tolaga Bay – Uawa will host international celebrations for the Transit of Venus in June 2012.
Sydney Observatory will have special programs available on 6 June 2012.