This page offers all the information you need in order to observe the next transit of Venus on 2012 June 5 and 6 succesfully, ranging from the prediction of your local circumstances to the weather prospects.
Your local circumstances are computed below. You can change this location by either dragging the marker on the map, searching for an address or entering the longitude and latitude. When entering the longitude and latitude in degrees and decimals, please consider east longitudes and north latitudes as positive. The height is measured in meters above sealevel.
Notes on the data
Planetary transits start when the planet’s disk is externally tangent with the sun (ingress, exterior). From then, the planet may be discerened as a little black dent in the solar limb, gradually growing bigger until the entire planet is seen on the solar disk (ingress, interior). During the next five to six hours, the planet will traverse the sun’s disk until the planet’s disk will touch the opposite solar limb (egress, interior). The transit ends when the planet’s disk is externally tangent with the sun (egress, exterior).
For all four contacts, the local time, the position angle of Venus, the angular distance to the sun’s centre and the sun’s altitude and azimuth are given. If the sun’s altitude is negative, this means that the sun is below the horizon and, subsequently, the particular contact will not be visible from the specified location. This is indicated by an asterix. The azimuth is the compass direction, measured eastward from the north. The approximate times of setting and rising of the sun on June 5 and June 6 are given in local time. Instead of sunrise and sunset, you can also choose to show the start and end of more ideal observing conditions, when the sun is at least 8° above the horizon. Finally, the mean cloud amount in June is given, indicating the probablity that clouds might interfere with your observation of the transit of Venus. The time zone offset and daylight saving time are selected automatically, but you can change these if you want to.
You can compute the local circumstances for any instant between ingress and egress using the slider (Safari and Opera only). Not only are the position angle, angular distance and the sun’s altitude and azimuth updated when you move the slider back and forth, the position of Venus on the solar disk at the selected instant is also indicated in the diagram right to the map.
Note that the times of contact published elsewhere may differ by a couple of seconds from the ones presented on this website. These differences arise when a diameter of Venus is chosen which refers to the planet’s crust rather than to the top cloud level as seen from earth. Also, another prediction of the difference ΔT between Dynamical Time and Universal Time in 2012 may have been used. This website uses 68 seconds, based on extrapolated values from the IERS Rapid Service/Prediction Center. Finally, the computations on this website do not take into account the effect of atmospheric refraction.
The diagram next to the map shows the movement of Venus across the solar disk relative to the zenith, the point directly overhead. This is how you will see Venus advancing on the solar disk when observing with the naked eye or a telescope on an altazimuth mounting. Because of the diurnal motion of the celestial sphere, the sun’s disk rotates with respect to the direction of the zenith in the course of a day. The initially straight chord, representing Venus’ trajectory with respect to the north point, is now transformed into a curved path. The gray disks of Venus indicate the invisible part of the transit during which the sun is below the horizon. The line along the solar disk indicates the direction of the celestial north.
General circumstances
The diagram below, drawn to scale, shows how Venus will traverse the solar disk as seen from the centre of the earth. The five positions of Venus along the time-scale are the exterior (1) and interior (2) contacts at ingress, the least distance to the centre of the solar disk (m) and the interior (3) and exterior (4) contacts at egress. The position angle of Venus is measured counterclockwise along the solar limb from the direction of the north on the celestial sphere (N).
The transit of Venus of 2012 June 5-6 for a geocentric observer. The top of the diagram points to the north.
The geocentric circumstances for the 2012 transit are summarized in the following table. The times are in Universal Time.
| contact | time | position angle / separation |
| 1. ingress, exterior | 22.09.29 | 40.7 |
| 2. ingress, interior | 22.27.26 | 38.2 |
| minimum separation | 01.29.28 | 554".4 |
| 3. egress, interior | 04.31.31 | 292.7 |
| 4. egress, exterior | 04.49.27 | 290.1 |
At the time of the transit the sun measures 1891.38 seconds of arc across, while Venus is only 58.26 seconds of arc in diameter. This makes Venus just visible to the unaided eye as a small black dot. When fully on the sun’s disk, Venus covers only 0.1 percent of the sun, so you won’t notice any decrease of sunlight during the transit. Therefore, it is essential to use a safe solar filter! See the Observer’s Guide on this website for more information on viewing the transit of Venus.
The transit will be wholly visible from eastern Australia, New Zealand, New Guinea, the Philippines, China, Korea, Japan, the islands of the western Pacific Ocean, Hawaii, Russia, Alaska and north-west Canada. In the far north the entire transit can also be seen, since the sun does not set. From eastern Canada, the United States, Central America, the Caribbean and northwest South America only the first part of the transit will be visible, because first contact occurs in the afternoon of June 5 and the sun sets while the transit is still in progress. In western Asia, Europe, the Middle East and eastern Africa only the last part of the transit will be visible. On June 6 the sun will rise with Venus already on its face and last contact will be seen in the morning hours. A special case forms a triangular area from Iceland downwards. Although both ingress and egress will be visible, the transit won’t be visible in its entirety. Due to the short summer nights at these latitudes, the sun sets after ingress on June 5 and rises before egress on June 6, leaving only the middle part of the transit invisible!
Visibility of the transit of Venus. (Image © Steven van Roode)
You can download a large world map which shows the world visibility of the 2012 transit of Venus in more detail. A Google Earth file draws the visibilty area and the bounderies across the earth’s surface in Google Earth.
Extreme values
Owing to the effects of parallax, arising from both the latitude of the place and its diurnal motion imparted by the earth’s rotation, the ingress and egress as seen from a point on the surface of the earth will occur a little earlier or later than when viewed from the centre of the earth. There are locations where a specific contact will be most accelerated or most retarded by the effects of parallax. Because these locations are favourable for Delisle’s method of finding the sun’s distance, they are called Delislean poles. The sun is on the horizon at each contact listed below: setting at ingress and rising at egress. You can download a world map, which shows the differences at ingress or egress in more detail.
| contact | time | position angle | longitude | latitude |
| 1. most accelerated | 22.02.55 | 41.5 | –37.6166 | +43.6590 |
| 1. most retarded | 22.16.07 | 39.8 | +140.4070 | –45.1330 |
| 2. most accelerated | 22.20.39 | 39.1 | –40.2196 | +45.6760 |
| 2. most retarded | 22.34.17 | 37.1 | +138.0414 | –47.3720 |
| 3. most accelerated | 04.24.37 | 293.7 | –166.2566 | –22.0440 |
| 3. most retarded | 04.38.16 | 291.6 | +11.2411 | +20.1750 |
| 4. most accelerated | 04.42.48 | 291.0 | –169.6079 | –19.5860 |
| 4. most retared | 04.56.00 | 289.2 | +7.8442 | +17.9830 |
As a result, the apparent stay of Venus on the sun’s disk will also vary according to an observer’s location. There are two locations where the transit’s duration will arrive at its extreme values, but only one is in the area where the entire transit will be visible. These points are sometimes referred to as Halleyan poles, because the largest difference in duration is most favourable for finding the sun’s distance using Halley’s method. For the 2012 transit of Venus, the location where you might experience the shortest duration is positioned well in the area of visibility, near 38 degrees south and 170 degrees east, not far from the North Island of New Zealand. This makes the west coast of the North Island of New Zealand an excellent observing site insofar the determination of the solar parallax is concerned.
Difference between the transit’s topocentric duration and the geocentric duration, irrespective of the visibility. In red shaded areas the transit will last longer than as seen from the centre of the earth. Purple shaded areas indicate a shortened duration. (Satellite data provided by The Living Earth ®Inc./Earth Imaging; diagram courtesy François Mignard, Observatoire de la Côte d’Azur)
The other Halleyan pole, where the duration will be longest, is located at the opposite, near 38 degrees north and 10 degrees west, which is very close to Lisboa in Portugal. But the transit will not be visible from this location. The location on land within the area of visibility that will experience the longest duration is the south coast of Iceland, at about 63.5 degrees north and 18 degrees west. So, obervations from the south coast of Iceland, paired with observations from the west coast of the North Island of New Zealand, will yield an accurate value of the solar parallax using Halley’s method of durations. You can also download a world map, which shows the difference in duration in more detail.
Weather prospects
The following weather map shows the world-wide mean percentage of daytime cloud cover in June. The color scale gradually varies from red to light blue, corresponding to a totally cloud free sky and a completely cloud covered sky, respectively.
Weather map showing the mean cloud cover in June. (Satellite data provided by The Living Earth ®Inc./Earth Imaging; cloud cover data obtained by the International Satellite Cloud Climatology Project)
The most favourable sunshine prospects are for Australia and Hawaii, with a relatively low probability of cloudiness. Especially Arnhem Land offers the best chance for clear skies. At the onset of the monsoons, East Asia has dismal prospects. Russia, Japan and north-west Canada, being in a midlatitude zone of migratory low-pressure systems, tend to be cloudy, except for a small part of Alaska and Canada’s Yukon Territory.
Links
When this page is loaded, it starts with a default geographic location based on the viewer’s IP-address. If you would like to link to this page starting with another default location (for instance your observatory or planetarium) you can append a query string to the url, with parameters lat and lon specifying the latitude and longitude respectively. Example.
The website of Chuck Bueter provides an extensive collection of links to different subjects related to the transit of Venus.
The website of Robert van Gent provides a bibliography of sources relating to the transit of Venus, with links to many of the original publications.
Copyright and acknowledgments
All text, maps, diagrams and calculations are made by Steven van Roode, unless stated otherwise. The times of contact are computed using the iterative algorithm and Besselian elements provided by Jean Meeus in his book Transits (Willmann-Bell, 1989). The Javascript code is based on a script by Franco Martinelli. The localized geographic content is generated by MaxMind. The height, time zone offset and daylight saving time data are obtained from Geonames. The mean cloud amount is based on data of the International Satellite Cloud Climatology Project.