2012 Transit of Venus

When Venus passes directly between earth and the sun, we see the distant planet as a small dot gliding slowly across the face of the sun.

The next transit of Venus occurs 6 June, 2012.  Observers in or near Tain will see the transit at sunrise : 04:19, transit ends 5:36. This will be the last transit of Venus to occur in your lifetime.

Tain & District Field Club will not be organising a special trip to view the transit – we want you to be aware and be prepared for 6th June.  And to view safely!

DO NOT LOOK DIRECTLY AT THE SUN WITH YOUR BINOCULARS OR EVEN NAKED EYE – you could permanently damage your vision.

Transit of Venus June 2004Click image to view

Some will recognise Tain Royal Academy in these pictures and the good weather in 2004.

Here are some links regarding Venus and its transit across the sun:

Good one – lots of info and an iPhone or Android app to give GPS based timings


The technical astronomy article

Eclipse Glasses supplier

David McAllister produced this below as further background material.  One has to keep in mind the importance in the history of science of observing Transits of Venus – and how rare they are.

The transit of Venus – 6th June 2012

All day on 4th Dec. 1639 William Horrocks the curate of Hoole, near Preston, watched the sun projected from his telescope into a darkened room.  He records in his diary that at 3:15 p.m. he “beheld a most agreeable spectacle, a spot of unusual magnitude and of a perfectly circular shape, which had already fully entered upon the Sun’s disk on the left, so that the limbs of the Sun and Venus were precisely coincided.  Not doubting that this was really the shadow of the planet, I immediately applied myself to observe it.”  Horrocks had only until sunset at 3:50 to observe the transit but he and his friend William Crabtree 30 miles away are the first recorded observers of this phenomena.

It’s not often we get the chance to see something that occurs less than once in a lifetime.  Since Galileo invented the telescope this astronomical event has only taken place seven times (1631, 1639, 1761, 1769, 1874, 1882 & 2004).  On the 5th June at 11:09 p.m. the planet Venus will begin to pass directly between the Earth and the sun.  For the next six hours until 5:36 a.m. its tiny disc will creep slowly across the face of the sun.  Unfortunately for us most of the transit will take place before dawn, which should be at 4:19 a.m. that day.

Venus, the second planet in the solar system, orbits between the Earth and the sun but  because the orbits of the two planets are inclined at 3.4° usually, as we pass, Venus lies above or below the sun.  Transits of Venus (times when it passes directly between the sun and us) occur in pairs eight years apart at intervals of 121 and 105 years.  After the current pair (8th June 2004 and 6th June 2012) there will not be another transit until 11th December 2117.

Timing of the position of the planet as seen from different places on earth can be used to give an accurate measurement of the distance from the earth to the sun (a measurement called the astronomical unit or AU).  This in turn permits astronomers to measure accurately mush greater distances in the galaxy.

After Horrock’s observations the idea that the timing of Venus’s position to calculate the astronomical unit originated with James Gregory, a mathematician and astronomer born near Aberdeen who became Professor of Mathematics in St.Andrews in 1668.  Edmond Halley (of comet fame) developed Gregory’s work and persuaded the Royal Society in London of the merits of this method.  Despite being observed from more than 120 different places the 1761 transit proved to be of little use.  The knowledge of longitude and accuracy of timing were such that results were not good enough to improve on the measurements made 121 years earlier.  1769 however was much better with more accurate work being carried out by many expeditions including Captain Cooke’s to Tahiti.  The final measurements should have given a much more accurate AU, but the timing was affected by the “black drop effect” where the edge of the planet appears to be drawn out into a drop shape as the Venus crosses the edge of the sun.

By the time of the 1874 and 1882 transits astronomical techniques had advanced enough to refine the measurements and the AU was calculated to with in a few percent of the value we can now determine by radar.

In 2004 the measurements were carried out with unprecedented accuracy using information from many observatories on earth and satellite data.  Measurements of the light profile of the transit were also made to monitor the slight darkening of the sun.  These have since been used to refine the techniques used to detect planets around other stars.

Before the 1882 transit William Harkness of the U.S.Naval Observatory, Washington wrote:

“We are now on the eve of the second transit of a pair, after which there will be no other till the twenty-first century of our era has dawned upon the earth, and the June flowers are blooming in 2004.  When the last transit season occurred the intellectual world was awakening from the slumber of ages, and that wondrous scientific activity which has led to our present advanced knowledge was just beginning. What will be the state of science when the next transit season arrives God only knows. Not even our children’s children will live to take part in the astronomy of that day. As for ourselves, we have to do with the present…”

What would he have thought of a world where we can all submit our timing of the event using iPhone or Android apps (see www.transitofvenus.org).  However once the 6th June has passed we also will be left to wonder “what will be the state of science when the next transit season arrives” in 105 years.  “As for ourselves, we have to do with the present…”


You should never look directly at the sun using telescopes or binoculars.  The retina can even be damaged by looking at the sun with the naked eye so proper eclipse glasses should be worn or a projected image used.

David McAllister, May 2012

the June 2004 Transit of Venus
Safe solar viewing equipment
Safe solar viewing technique at Tain Royal Academy
The Result - 6th June, 2012, Sunrise at 05:35 BST

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