Monday, 4 June 2012

This century’s last transit

This century’s last transit

Tomorrow you will be able to witness a celestial spectacle no one will ever see again this century: a transit of Venus. While Venus starts to slowly pass between Earth and Sun, millions of people will look in awe at the planet’s silhouette against the brilliant solar disk, beholding the actual clockwork movement of our solar system. It’s one of the most infrequent of planetary alignments, and its rarity alone should already justify your own observation of the transit. If you miss this one, you will have to wait another 105 years until the snow is falling in December 2117.
Because of its rarity, viewing the transit yourself not only connects you to the hundreds of astronomers in history who set out on perilous journeys to measure the Sun’s distance using the transit of Venus, but also to your descendants who will see it again in the next century: it will make you part of a chain of privileged people to whom Venus reveals her black profile backdropped by the solar disk.
There are four distinct stages of the transit: when Venus starts to move unto the solar disk (1) there will become visible a small black dent on the solar limb, which will grow larger when time passes by. After nearly 18 minutes, the disk of Venus is on the solar disk in its entirety (2), touching the solar limb on the inside. From then on Venus parades in about seven hours to the other side of the solar disk, where the planet will touch the solar limb first on the inside (3). Just 18 minutes later the shadow of Venus will have left the solar disk once more (4) – the transit is over.
Not all stages might be visible from where you are. Find out which part of the transit you can see using our calculator of local transit times.

During the stages at the start and end of the transit, two special phenomena may be seen. While Venus is partly off the solar disk (1 and 4), light scattered by the planet’s dense atmosphere will produce a thin, luminous ring around the silhouette. This effect, called the aureole, was already seen during the 1761 transit of Venus and has helped astronomers to investigate the composition of the atmosphere. Tomorrow astronomers will yet again turn their instruments to the aureole to analyse the structure of the Cytherean atmosphere.
When Venus touches the solar limb on the inside (2 and 3) a greyish haze between the two limbs may become apparent, depending on the quality of the applied optics. In the 18th century this optical effect caused the round shape of Venus to deform extremely, hence its name black drop effect. With larger telescopes the effect is less manifest.

Image credits: left image by Lorenzo Comolli, right image by Paul Dolk.
Whenever you have the chance, you should observe the transit yourself. But be careful: only look at the sun with proper eye protection, on pain of permanent loss of sight. Once safety precautions are met, you can enjoy the transit of Venus in several ways. Just peering through a telescope and discerning the small black dot of Venus can be a humbling experience: realising that Venus is about the same size of our own planet, our smallness in the vast Universe becomes readily visible before our own eyes. But there’s more you can do.
  • Use our free phone app to join a collective experiment to measure the Sun’s distance.
  • Picture the transit, either by sketching or photographing, and upload your creations to our gallery by sending it to
  • Enter Southern Stars’ Venus Transit Challenge, a photo contest for mobile devices.
  • Twitter about what you come across (use hashtags #tov2012 or #venustransit). The results of all these activities can be followed live using Esri’s web app, showing an interactive map with all observations recorded by users of the phone app, as well as tweets, pictures and videos appearing in social media.
  • Even if you’re clouded out, or if the transit isn’t visible from where you live, there are still many online viewing options to follow the event.

Out of Diaries: 3 June 1769

On 3 June 1769, as one location after another emerged from night to day, astronomers and amateurs across the world braced themselves. It was the last transit that any of them would ever be able to watch.
With more than eighty observers at thirty viewing stations in Britain and sixteen abroad (not counting the North American colonies), the British were clearly in the lead, followed by the French with almost fifty astronomers at eighteen locations in France and five overseas. There were astronomers in nine German towns, and Dutch observers positioned in Leiden. The Swedes were also prepared. Pehr Willhelm Wargentin had recruited twenty-one observers at nine locations in Sweden and Lapland. Anders Planman was safely installed in his observatory in Kajana and Fredrik Mallet – despite the fierce winter conditions and his bad mood – had made it to Pello on 12 May, late, but in time.
Eighteen astronomers were stationed at ten locations on Russian soil and on the North American continent forty-seven observers anticipated Venus’s appearance – from the local administrator of a mine near Mexico City to the ‘Surveyor-General of Lands for the Northern District’ in Quebec. More than thirty observers had spread out over twelve locations along the East Coast.
In Tahiti, after worrying about the cloudy skies, Captain Cook and his crew awoke to a clear sky and watched the black dot moving across the sun for six long hours. Chappe d’Auteroche also succeeded to view the transit in Baja California, as did Maximilian Hell in Vardø. In Pennsylvania, the American astronomer David Rittenhouse, couldn’t believe his luck when he woke early that day and saw the sky gleaming, as he described it, with a ‘purity of atmosphere’. Then just after two o’clock in the afternoon, as Venus readied herself to traverse the Sun, Rittenhouse became so over-excited that he collapsed and fainted, missing the beginning of the most important event of his scientific life.
There were observers everywhere. Catherine the Great played cards all night with her favourite courtiers so that they would not fall asleep and miss the transit. King George III was in his new observatory in Kew and in Jakarta a wealthy Dutch priest had built a lavish eighty–foot high observatory from where he viewed the transit. Le Gentil, however, in Pondicherry saw only clouds – having spent years chasing Venus he had failed to make any successful observations of the first and the second transit.
Around 250 official observers at 130 locations had waited for Venus. Now it was time to collect the results.


50 Years Ago: Fantasy and SciFi

Cover of Fantasy and Science Fiction
In June 1962, The Magazine of Fantasy & Science Fiction published a story entitled “The Transit of Venus” by Miriam Allen de Ford. The editor’s preface sets the stage:
It was to observe one sort of Transit of Venus that Captain Cooke  originally visited Tahiti — where, like Captain Bligh, who came there not long after, he had a devil of a time keeping his men from going native for love of local beauty and despite that need for Discipline which officials in every age and place are so certain is so good for us. Miriam Allen de Ford (whose infinite variety age cannot wither) departs for a different Venerian — and fie upon those who have it, Venusian — transit upon a more distant island, when and where, however, similar problems still exist.
Paul Doherty
Paul Doherty of Exploratorium
Despite its suggestive name, the magazine delves into straight science as well. Transit of Venus enthusiast Paul Doherty of the Exploratorium paired with Pat Murphy to write a story for the magazine in the January/February 2011 issue under the title “Science“. In it they feature historic expeditions, the black drop effect, exoplanets, and the Kepler mission. With a nod to the magazine’s readership they finish by noting,
Science fiction writers have been speculating about life on other planets for more than a hundred years (with Jules Verne writing about Moon
men back in 1865). We figure it’s about time that science caught up..

The transit from Down Under

The position of the Sun and Venus from the beginning to the end of the transit as seen from Adelaide. Drawing Nick Lomb
From New Zealand and from most of Australia all the six and a half hours of the 2012 transit of Venus is visible, weather permitting. From Western Australia the transit will already be underway as the Sun rises. Just because the transit is visible from beginning to end does not, however, mean that it will be easy to see all of the transit, for June is winter in the Southern Hemisphere and the Sun will be low in the sky.
As the Sun will be low in the sky prior planning is essential to see the required phases of the transit. For those who just want to see Venus on the Sun the best time will be in the middle of the transit when Venus is well inside the Sun and relatively high in the sky. It will be possible to take interesting photos at that time, especially if there are wisps of cloud around to give a sense of drama.

The position of the Sun and Venus from the beginning to the end of the transit as seen from Melbourne. Drawing Nick Lomb
Historically the more interesting phenomena occur at the beginning of the transit (ingress) as Venus moves onto the disc of the Sun and at the end of the transit (egress) as Venus moves off the Sun. The infamous black drop effect is a dark linkage joining the dark silhouette of Venus to the inside edge of the Sun at about the time of second and third contacts – when Venus appears to touch the inside edge of the Sun at ingress and then at egress. For James Cook and many other observers of transit in past centuries this effect made it difficult to time the contacts as accurately as they wanted.
Today we know that this effect depends on factors such as the size and quality of the telescope being used and the atmospheric conditions. With the Sun low in the sky during ingress and/or egress as seen from Australia and New Zealand there is a strong likelihood that some observers will witness the black drop effect. That will be an interesting and exciting link to the past.

The position of the Sun and Venus from the beginning to the end of the transit as seen from Sydney. Drawing Nick Lomb
From Adelaide the transit begins about half an hour after sunrise so the Sun is very low in the sky at that time. For those who want to see the ingress, clouds permitting, then a suitable location with good sightlines towards the north-east has to be found in advance. As at that time of the year the Sun does not change position much from day to day, it is possible to check possible observing spots a few days before the transit with the actual Sun.
As we move eastwards across the continent to Melbourne, we find that the Sun is a little higher, but still low in the sky at ingress. Conversely, at egress the Sun is starting to move towards the horizon. Further east from Sydney, again the Sun appears a little higher in the sky at ingress, but still low enough to be easily blocked by trees or houses.
It should be noted that ingress takes about 18 minutes and egress the same time, so that there is almost six hours in between them. This gives time to move observing locations between ingress and egress, if necessary. Some people may even want to go to a third location for the in-between time with Venus fully on the Sun.

The position of the Sun and Venus from the beginning to the end of the transit as seen from Auckland, New Zealand. Drawing Nick Lomb
Moving across the Tasman to New Zealand we find that from Auckland the Sun is quite acceptably high at the beginning of the transit. However, as there is always a price to pay for any gain, the Sun is very close to the horizon at the end of the transit.
It is dangerous to look directly at the Sun as permanent eye damage can occur. See Tim Cole’s post for the right word on eye safety. Still unless you really know what you are doing, it is best to check if there are transit viewing sessions held by your local observatory, planetarium or amateur astronomical society and join them if you can.

Where did the black drop go?

One of the most famous phenomena to look for during the transit of Venus on June 5/6 is the black drop effect. First noticed in 1761, this optical effect distorted the shape of the silhouette of Venus when the planet touched the solar limb on the inside, thus hampering the timing of the moment of contact. In the 18th century the shape of Venus was highly distorted, and the appearance of the effect lead to the metaphorical term ‘black drop’ (in latin ‘gutta nigra’). In the 19th century however, the drawings of the black drop effect look more like a greyish hue between the limbs of Venus and the sun, and reports of the last transit of Venus in 2004 show that many observers didn’t see the effect at all. What happened to the black drop effect? Where did it go?

It’s the cause of the effect that explains why the black drop was so evident during the 1761 and 1769 transits of Venus, and much less manifest in the later transits of 1874, 1882 and 2004. The black drop effect is produced primarily by the telescope: by blurring the image, the limbs of Venus and the sun are softened, creating a darker shade between the limbs that becomes the more visible the more the telescope blurs the image. Larger telescopes have sharper images, thus making the black drop effect less clear. So, it’s the better optics that made the black drop effect disappear in later years!
To be able to fully appreciate the reports of the 18th century astronomers on the black drop, it’s important to watch the transit with telescopes from that era. Randall Rosenfeld coordinates an experiment in which the upcoming transit will be observed with instruments from the late 1700s. It will help us to get a visual representation of the often only verbalised accounts. If you happen to own an antique telescope, join Randall and become a participant in experimental archaeology.
And if you don’t own antiques, just be on the lookout for the black drop effect, whether it will appear as a distortion of the Venus circular shape or will merely be a greyish hue.


Halley’s outrageous statement

There is no figure in transit history more significant than the second Astronomer Royal, the Rev’d Dr. Edmund Halley (1656-1742). His writings are of more than ‘mere’ historical interest, as they have framed the shape of the transit enterprise since the late 17th century. Some serious amateur observers and modern scientists have taken inspiration from his words. On the modern transit site of NASA’s Mr. Eclipse Guy (Fred Espenak) one can even find a late-Georgian ‘Englishing’ of Halley’s epochal 1716 paper on the solar parallax. Halley’s words are worth reading and re-reading, as much for the fruitful cultural echoes they may evoke, as for the ideas for modern science they may spark.

Halley’s texts may also harbour hidden surprises.
Astronomical writings in the 17th century were produced in an intellectual culture which favoured multi-dimensionality of meaning. A text was a layer cake, capable of conveying multiple significations by operating on several planes simultaneously. In this the ‘Scientific Revolution’ was continuing a practice inherited from Late-Antiquity and the Middle Ages. That venerable and vigorous inheritance placed astronomy in Halley’s day and for long after within the republic of letters, and not apart from it. Astronomers had a lively understanding of the classical allusions which permeated their Republic of Letters. Physical science decently clothed in ancient literary gestures was the style in which things were done, but it was more than that, for that vesture clothed a conceptual reality. The classical goddess Venus was the planet Venus.
In one of Halley’s most frequently repeated quotes, he states that the transit of Venus “is by far the noblest sight among astronomical sights”. We are told that he was moved to say this because the phenomenon gave the opportunity to measure the solar parallax with unprecedented accuracy. That is true, but it is not the whole story, for rarely are we given the full context. Halley is also telling a joke, which according to present lights is politically incorrect.
The full passage is:
Venus, in as much as she is the most beautiful of all the heavenly bodies—after the fashion of her sex—is not afraid to appear bereft of both borrowed attire, and alien lustre. This, in fact, is by far the noblest sight among astronomical sights, as impressive as the secular games… Through observing this unparalleled sight it will be possible to fix the distance of the Sun from the Earth with the utmost certitude (Venus quamvis syderum omnium speciosissima, more sexus sui, sine mutuato cultu ac splendore asscititio in conspectum prodire veretur: Hoc etenim spectaculum inter Astronomica longe nobilissimum, instar Ludorum secularium… Unico vero hos Observato summa cum certitudine distantiam Solis a Terra determinari posse…; De visibili conjunctione inferiorum planetarum cum Sole, Dissertatio astronomica, in Philosophical Transactions 16 [1691], 511-522, at p., 519, trs. RAR).
What is he saying?
When Venus is on the solar disc, she does not shine by borrowed light from the Sun, that is, she is bold and brazen enough to willingly appear to all in the sky without any clothes (“is not afraid to appear bereft of both borrowed attire, and alien lustre”). So when Halley says “This, in fact, is by far the noblest sight among astronomical sights” he is saying that “Starring through a telescope at Venus, the nude goddess of love, and a renowned beauty, is by far the noblest sight among astronomical sights!”. It’s a joke none of his learned colleagues could have missed.
Astronomical voyeurism, indeed. Horrocks said something similar in the aftermath of the 1639 transit:
This telescope liberates the pleasing face of Venus, and exposes her magnificent form freed from the excessive solar light with its rays, and her body from the shadows (Hic [tubus] gratam Veneris faciem nimiaque superbam/ Luce suis nudat radiis, corpusque tenebris/ Vindicat…; Johannis Hevelii Mercurius in Sole visus Gedani… Venus In Sole pariter visa… a Jeremia Horroxio [Gedani: Autoris typis, et sumptibus, 1662], pp. 111-145, at 114, trs. RAR. The Whatton translation of 1859 is unreliable).
The astronomers only  have themselves to blame for the 18th-century satirists likening them to peeping Toms.
I will, nonetheless, join the ranks of the Toms peeping heavenwards on June 5th-6th. I’ll be in good company.

World wide map of the transit

The transit of Venus will soon captivate the world. Millions of people will be turning to the Internet to experience this rare event. One popular way to view the transit will be through live video streams from telescopes. Another way to learn and share experiences about the transit is through one of our oldest story-telling devices: the map.
Maps have figured prominently in the history of the transit of Venus. In 1760, Joseph-Nicolas Delisle created an influential transit map that guided many of the international expeditions of 1761 and 1769. In the late 19th century, Richard Anthony Proctor drafted a series of maps and diagrams that explained the geometry of the transit to the public. Many other examples can be seen in this archive of historical maps.
It is now our turn to tell our stories of the transit of Venus through maps.

Opening page of the Transit of Venus web app at
This new transit of Venus web app has just gone live at and invites you to learn about the transit, see observations in real time, and share your experiences of this special and rare event. The web app is a dynamic and participatory platform that offers these ways to encounter the transit and interact with others:
  • You can find where and when the transit occurs around the world
  • You can view contact timing observations from the VenusTransit smartphone app in near real-time on transit day and compare observed contact times with predicted contact times (most of the timing differences can be attributed to the black drop effect)
  • You can find tweets, pictures, and videos of transit of Venus activities on the map and share your experiences by using these hashtags and key phrases: #tov2012, #venustransit, ‘Transit of Venus’, and ‘Venus Transit’
  • You can watch a video which briefly explains the transit and provides a visual animation that compresses the 6 hours and 40 minutes of the transit into one minute
On transit day, this web app will also be embedded at several places including this web site, Astronomers Without Borders, and eclipse-maps.
The transit of Venus web app was developed jointly by the prototype software laboratory from Esri, the GIS software company (and my employer), Astronomers Without Borders, and the Dutch team behind the VenusTransit smartphone app and this website.

Out of Diaries: 28 May 1761

In early April 1761, just after rounding the Cape of Good Hope, Alexandre–Gui Pingré’s ship met a damaged French supply vessel that had been attacked by the British. Packed to the brim with provisions from the Cape for Mauritius the captain ordered Pingré’s vessel to accompany and protect them. Instead of sailing to Rodrigues where he had been ordered to view the transit on 6 June 1761, Pingré was now forced to go to Mauritius where he disembarked on 7 May.
It was still possible to reach Rodrigues in time – an eight-day journey and no more, one captain had told Pingré. However, squalls and high waves had slowed them down first, then a lull. The days were ticking by and the frenzied race had come to a standstill. On 26 May, Pingré finally saw Rodrigues in the distance – a sight ‘that filled me with such satisfaction as I haven’t felt since my departure from France’, he cried, but there was still no wind. He was now, Pingré believed, in the hands of God and the captain. ‘The calm continued on the sea, in the air and in the spirit of M. Thullier [his assistant]’, he wrote in his journal, ‘but certainly not in mine’.
Then, on 28 May, only seven days before the transit, Pingré finally set foot on the ‘desired island’. There was no town or fort on Rodrigues. The only reason the Compagnie des Indes kept the island was for its large turtle population. Regarded as a remedy against scurvy, the turtles were collected and kept in an enclosure and every two or three months dispatched to Mauritius. The governor of Rodrigues, Pingré snobbishly noted, lived only in a small log cabin made of roughly hewn timber and mud. Pingré and his assistant had to sleep in a shed with a dirt floor beside this governor’s ‘residence’.

‘We had no time to lose’, Pingré wrote. He found a location in the north of the island from where to view the transit, but it was too late to build a proper observatory. Instead he placed some big boulders in a circle and constructed a small hut to house the instruments. It was so crudely built that it gave little protection from wind, dust and animals. The instruments had already suffered from the long sea voyage with some ‘eaten by rust’, Pingré moaned, hectically polishing and greasing them with turtle oil, the only lubricant available. Over the next days, the French astronomer prepared his instruments and observed the movements of Jupiter’s satellites at night in order to set the clock – an enterprise that was sabotaged by the rats that chewed through one of the pendulums. He only had a few days to the transit.

The earlier music of the transit

The cultural reverberations of the 19th century transits seem to have been of less amplitude and frequency than one might expect. The only sculptures of note are the 1883 bas relief Le Passage de Vénus by Pierre-Bernard Prouha (Observatoire de Paris), and the commemorative medal by Alphée Dubois (1877), apparently commissioned by the Institut de France and the Academie des Sciences. Paintings on canvas, such as John George Brown’s of 1883 showing preternaturally clean transit-observing urchins, and frescos, such as  Dupain’s 1886 Passage de Vénus devant le Soleil, can be counted on the fingers of one hand. For imaginative literature, there is the novel by John Philip Sousa, The Transit of Venus (Boston: Small, Maynard & Co., 1920) ― according to Jay Passachoff this novel should be issued with a health warning; Sousa is no Jules Verne. As for music inspired by the transit, it can best be characterized as ephemeral. The list of composers is headed by the redoubtable Sousa, and his and similar works can be sampled thanks to a Library of Congress web site.
What, then, of the 17th and 18th centuries?
Historiographies of progress, and popular historiographies—often the same thing—have taught us of the central role of the constructs “scientific revolution” and “enlightenment” in the formation of our world. Viewing the 17th and 18th centuries through that filter, we have been encouraged to see the period as the first great age of heroic astronomical and geodetic expeditions. A romantic view of such undertakings engenders romantic expectations; surely the sacrifices which left some astronomers stranded in exotic locales between transits (Le Gentil), or placed them between enemy combatants (Mason and Dixon), or made them martyrs to science with their observations alone as cenotaphs (Chappe d’Auteroche) must have created a very visible mark on the literature, art, and music of the time.
If they did, the mark has faded. The only narratives were those written by the astronomers themselves, the only graphic art was that produced for the astronomers’ books, and as for the music, at first sight it doesn’t seem to have been composed. One might have expected Urania’s sister Euterpe to have paid her some compliment in the France of Maupertuis and Messier, a culture with a seemingly inexhaustible taste for programmatic and evocatively titled music.
The explanation might lie in the fact that astronomers and their doings may not have been of sufficient social elevation or cachet to have had pieces named after them. Musicians, like astronomers, always had to have an eye on funding, which in the 17th and 18th centuries meant courting sources of patronage. For the former, this meant naming pieces after noble patrons or the stock figures from bucolic, chivalric, or otherwise mythic literary landscapes with whom they identified. Who knows, but research may yet reveal that the likes of the Marquis Cornelio Malvasia, the Chevalier Jacques d’Allonville de Louville, the Comtes de Cassini de Thury, and the second Earl of Macclesfield did have notable music dedicated to them. If so, the question then becomes “Was it because these noblesse d’épée and noblesse de robe were sources of patronage, or distinguished astronomers, or both?”.
Perhaps the search for transit of Venus related music ought to be conducted several cultural registers down from the sources of noble patronage, and the musicians in pursuit of them. Are there transit of Venus pieces lurking within the corpus of 18th-century broadside literature? That research has yet to be conducted.
There is yet a third possibility, namely that we’ve not looked in the right places for 17th-18th century transit of Venus music. If we ask, “How did astronomy and music function in the culture?”, the field of candidate pieces widens. Astronomy at the time was part of, not apart from, the republic of letters. A lively awareness of classical allusions permeated that republic. The classical goddess Venus was the planet Venus. In that world, a musical reference to Venus could have been heard as a reference to both the goddess and the planet. So any piece named for Venus could have functioned socially as a piece of music about the transit of Venus. Even music without an obvious textual or aural connection to the transits could be situated to function as transit of Venus music. Steven has amply demonstrated this with his account of Fr. Maximilian Hell, sj, and Fr. Johann Sajnovics, sj, singing the Te Deum laudamus to mark the dispersal of clouds and their successful observation of  the 1769 transit. This is a more promising perspective.
In the world of Dr. Edmund Halley, it allows us to view a work such as John Blow’s (1649-1708) masque Venus and Adonis (ca. 1683) as a prospective transit of Venus piece. The same would hold for any work derived from it. How so? Simply that Halley, his Royal Society colleagues, and anyone hearing music from the masque or improvised music based on it in light of his seminal 1691 and 1715 papers could have been put in mind of the potential of the 1761 transit―aural associations can work like that. What might such a piece have sounded like? If constructed according to late 17th-century conventions, and, say, based on the chaconne from Blow’s Venus and Adonis, and played on a reproduction of a transverse flute from ca. 1700, it would sound like the piece at the head of this blog.
Likewise for Venus-themed music of the 1760s. In the collections of Harvard’s Loeb Music Library is a print (Merritt Mus. 627.3.710) of J.C. Bach’s A Second Collection of Favourite Songs Sung at Vaux Hall…(London: Welcker, n.d. – the “London” Bach was J.S. Bach’s youngest son). One of the texts is “Smiling Venus Goddess dear” (pp. 7-10). The ownership inscription reads “George Brooks his Book[,] May 3, 1769″. Was George Brooks reminded of the upcoming transit on June 3rd when he viewed, performed, or listened to the piece? It is attractive to imagine the possibility.
The music is performed by R.A. Rosenfeld, on a transverse flute in boxwood by Ronald Wick based on an instrument by Hotteterre (Paris, ca. 1700) a’=392Hz, now in Graz, Universalmuseum Joanneum No. 08447*1384. The divisions are modelled on those in The First and Second Part of the Division Flute Containing the Newest Divisions Upon the Choisest Grounds for the Flute [=recorder] as Also Several Excellent Preludes, Chacon’s and Cibells (London: J. Walsh―J. Hare―P. Randall, n.d. [=ca. 1706-1708]).

Iconic pictures of the transit

Once the transit of Venus is over, we only have pictures and drawings to get a visual remembrance of the event. Some photographs have the quality to become iconic: they are used in books, pamphlets and posters and in some way represent a particular historic transit all by themselves. For the transits of 1882 and 2004 there are indeed two well-known iconic pictures:

The one on the left was taken on 6 December 1882 by the photographers of the American expedition stationed at Cedar Keys, Florida. Of the hundreds of photographic plates exposed by the eight American transit expeditions, only eleven from Florida have survived. Taking pictures of the transit was almost a military operation, the photographic apparatus a huge construction. A clock-driven siderostat reflected the sun light through a lens of long focal length towards a light-tight photographic house, where a sharp 4-inch image of the Sun was formed on the photographic plate. The plates had been prepared in advance with a dry collodion emulsion. The chief photographer would place one of these light sensitive plates in a special holder, and expose the plate by slowly moving a slit in front of it. An assistant would take the time, temperature, atmospheric pressure as well as the plate number, time of exposure and direction in which the slit was moved, and write all these numbers down in a log book. A second assistant would then take the exposed plate and put it carefully in a storage box. In Cedar Keys, this operation was repeated 150 times during the transit of Venus – an average of one plate every 2.5 minutes! Imagine the heat and pressure in the small wooden photographic hut, where three men diligently performed their repetitive tasks without time for even a short tea break. It’s a miracle that a small portion of the product of their hard work survived until today and became a mainstream icon for the nineteenth century photographic results.
In 2004, another miracle caused the work of David Cortner to become widespread. On the morning of 8 June the weather looked so dreadful at Connelly’s Springs, North Carolina, that David didn’t even care to observe the transit at first. From an overlook above the Catawba River he met with fog and clouds before sunrise:
Waiting… fifteen minutes till sunrise. Fog down on the treetops, a threat of rain. I wouldn’t have bothered but for the thought that if James Cook would sail halfway around the world to see a transit, who am I not to get up early for the same opportunity? Just the same, I’m thinking it’s a good thing I brought something to read.
The Sun emerged about 6:30 with a ghostly Venus near the end of its transit. Timestamps applied by the camera show that the sky was clear enough for photography twice, and the two intervals totalled a little more than 12 minutes. This is about as clear as it ever got. Immediately after, the overcast became complete, and I did not see the Sun again all day. Nice timing!
The photographs were made with a Nikon D100 and an Astro-Physics 5-inch F6 refractor. The Sun, shimmering through the fog, with the black disk of Venus on it resulted in eye candy pictures that appear everywhere today, from brochures, posters and websites to newspaper articles. All the drama and beauty of observing a transit of Venus is perfectly captured in a single shot. To me, David’s picture bears a strong resemblance to B. Mourik’s image in the August issue of Maandelijkse Europeese Mercurius in 1761. It was this engraving on the cover of J. van der Bilt’s Venus tegen de zonneschijf (1940) that got me hooked on the transit of Venus more than a decade ago.
Who will make the most recognisable picture of the 2012 transit of Venus on June 5 and 6? Will it be you? Who knows. Be sure to upload your pictures to our online depository by emailing them.


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