2012 Venus Transit

Up until a few years ago I had never heard of a Venus transit, much less any idea of its scientific and historical significance. I don’t even remember reading or hearing about the 2004 transit. To me Halley was the name of a comet, and Mason and Dixon had made up a line between the North and the South that had something vaguely to do with the Civil War. Delisle, Le Gentil, and Chappe were names completely unknown to me. On the day of the transit in June 2004 I was wandering around the bucolic countryside of Normandy having only two days earlier attended the 60^thAnniversary ceremonies of the D-Day invasion of France. Transits, astronomical units, and parallax meant nothing to me. That all changed a few years later.

What is a Venus transit?

A transit of Venus takes place when the planet Venus passes directly between the Sun and the Earth, becoming visible against (and hence obscuring a small portion of) the solar disk. During a transit, Venus can be seen as a small black dot moving across the face of the Sun. The duration of such transits is usually several hours (the transit we observed in 2012 lasted 6 hours and 40 minutes). A transit is similar to a solar eclipse by the Moon. While the diameter of Venus is more than three times that of the Moon, Venus appears smaller, and travels more slowly across the face of the Sun, because it is much farther away from Earth.

Fortunately, three astronomers in Europe, most notably French scientist and priest Pierre Gassendi (1592-1665), witnessed the transit of Mercury. In doing so, they became the first people to view a planetary transit with a clear understanding of exactly what they were seeing. Gassendi also looked for the predicted transit of Venus, but the transit had already ended before the Sun rose from his Paris location.

Sadly, no documentation exists of anyone in the world seeing the 1631 Venus transit – a missed opportunity. Given the fact that Venus’s silhouette is big enough for people to see with their naked eyes, it is likely that a few people around the world saw Venus as they glanced at the Sun (particularly around sunrise or sunset). But without access to the published materials possessed by a small number of educated Europeans, they would not have recognized what they were seeing.

I first learned about the 2012 Venus transit during a cruise in the Western Pacific to observe the 2009 solar eclipse but did not give the transit much thought at the time. After all, it was three years into the future, and I was working full time and had other travels plans for the next few years. The 2009 solar eclipse was my second. I saw and successfully photographed the 2006 eclipse in Turkey. These two solar eclipse experiences ignited a little spark in my brain that over the next couple of years began to glow brighter to illumine my mind to other astronomical phenomena that I wanted to see and experience. To that end, I saw and photographed the Green Flash while on a layover in Fiji in 2009. When I learned about the 2012 Venus transit, it seemed only natural that I should see it and to try to photograph it, too.

Even though I have seen and photographed a solar eclipse, it is not quite fair to describe myself as an astronomer, not even an amateur astronomer – I do not own a telescope. And, I can only say that I am just a little bit more of a photographer than I am an astronomer, which is not really saying much. I am very much a novice in both fields. But I have a wanderlust interest in travel and experiencing what the world has to offer. After all, the 2012 transit would be the last in my lifetime; I could not let this opportunity pass.

Location

It simply would not do to try to see only a partial transit in my home state of Indiana where the weather might not cooperate. As with other celestial observations, the weather is always a crapshoot (I have lost track over how many times a cloudy horizon has prevented me from seeing the Green Flash). Also, I wanted to try to photograph the event using an equatorial mount with a motor drive system that would allow me to track the event without having to constantly move the camera, as I had to do during the 2006 eclipse. I also wanted to take a photograph every five minutes so I bought a programmable shutter release that would allow me to not have to touch the camera at all throughout the transit. Since I was investing in equipment that was no little expense, I wanted to see the transit somewhere that maximized the chances of seeing all of it. I booked a tour for my wife, Blythe, with Insight Cruise, a tour organization that specializes in tours to watch solar events, especially solar eclipses. They were taking a group to the Big Island of Hawaii where there was a very good chance we would be above any clouds on the slopes of Mauna Kea, thus enhancing the chances that we would see the entire transit, 1^st contact to 4^th.

Our hotel during our stay on the Big Island was on the northwest side of the island. Kailua-Kona is the site of the start and finish of the Hawaiian Ironman World Championship, which has nothing to do with the transit.

This map indicates the path of the transit across the surface of the earth. The red circle indicates that part of the earth where the entire transit is visible. The blue circles indicate that part of the earth where only a partial transit is visible. The green circles indicate where the transit is not visible. Hawaii was the only place in the Unites States where the entire transit was visible – but just barely.

Equipment

In January of 2012, I attended the monthly meeting of the local astronomy club in West Lafayette near where I live. At this meeting I got to know one of its members, Franz, who far exceeds the definition of amateur astronomer, and who he is a gifted teacher. He told me what equipment I would need to photograph the entire transit.

I already had a Canon 5D MK II DSLR camera and the 200-500mm zoom lens that I had used to photograph the 2006 eclipse, but that would not be enough for what I had in mind for the transit. Since the transit would last longer than six and a half hours, I did not want to have to keep adjusting the camera all day. That would be too tedious and would distract me from watching and enjoying the transit. I needed something that would do all the work for me. I needed to shell out some cash.

At the time, this was the camera I started out using to photograph the transit.

I mail-ordered an Orion AstroView Equatorial telescope mount, an Orion EQ-3M dual-Axis electronic drive, and a full aperture solar filter for my lens. When it arrived, I had no idea how to put it all together. I read the directions but was hopelessly lost; I needed help. I invited Franz to come over to help me figure it all out. Franz not only has a thorough knowledge of astronomy and photography but has an infinite capacity for patience. He helped me put the mount together and showed me how to set it up so that I could track and photograph the sun. Eventually, I got it all working. I only needed to practice with it. In May I took my first photo of the Sun. When I looked at it on my computer, I thought there must be a smudge on my lens. But, as the Sun kept moving through the viewfinder, the smudge moved with it. It finally dawned on me that my lens was fine; the smudges were sunspots. I took photos of the sun everyday for the next few weeks for practice (we had lots of clear skies in Indiana in May that year) using the sunspots as a surrogate for Venus. I kept every photo and watched with fascination as the spots moved around the sun. Franz told me not to worry about the fuzzy appearance of the sunspots; Venus would be much darker and more distinct.

This is the Orion AstroView Equatorial telescope mount that Franz helped me assemble. With my camera mounted on this tripod, and if it all worked properly, I would not have to constantly reposition the camera to keep the Sun in the viewfinder.

These are the components of the dual axis electronic drive used to move the camera so that it tracked the Sun. The buttons are used to move the camera up and down, and right and left to keep it in the viewfinder. I used these occasionally to reorient the camera. It was tedious, but it worked.

A full aperture solar filter. Using the three screws, the filter can be securely fastened to the lens. It will filter the Sun so that it can be observed by the naked eye and without harming the camera lens.

When I first tried out my new gadget I pointed the camera at the Sun and took several photos. The solar filter worked as expected but I was disconcerted by what appeared to be a smudge over the Sun disk. But with subsequent photos it appeared the smudge was moving and that is when it dawned on me that the “smudge” was in fact a sunspot. The Sun color difference between these two photos reflects different shutter speeds as I experimented with the camera setting to find the best. I liked the one on the right best.

Technical Stuff

In transits and eclipses there are four distinct beginnings and ends that astronomers talk about. These are referred to as contacts. Here is an illustration of the four contacts during the 2012 transit.

First contact: the smaller body is entirely outside the larger body, moving inward (“exterior ingress”)

Second contact: the smaller body is entirely inside the larger body, moving further inward (“interior ingress”)

Third contact: the smaller body is entirely inside the larger body, moving outward (“interior egress”)

Fourth contact: the smaller body is entirely outside the larger body, moving outward (“exterior egress”)

Since the planetary orbits of Venus and Earth are essentially co-planer, when the planet Venus interposes itself between the Sun and the Earth, as in a transit, Venus appears as a small black dot on the disk of the Sun. Depending on the observation point on the Earth, the black dot of Venus will appear on different parts of the Sun. This difference, using simple trigonometry, can be used to calculate the distance between the Earth and Venus, which, using Kepler’s 3rd Law of Planetary Motion, yields the Astronomical Unit, which in turn can be used to calculate the distances between the planets of our Solar System.

Using two distant points of observation (d) from the Earth, and the timing of the Venus transit, which yields 𝜶, the distance between the Earth and Venus, D, can be measured using simple trigonometry.

The relative distances from the Sun to the other planets of the Solar System and the actual distance in miles. These distances could be calculated once the Astronomical Unit was determined by timing the Venus transit.

History

Merely observing and photographing the transit would not be enough to satisfy my curiosity about the event. To gain a better perspective and understanding of the historic and scientific significance of the transit, I read the book, Chasing Venus, by Andrea Wulf. This is a superbly written book that describes the historical significance of the transit and the trouble that 18^th Century astronomers had to go through to see, and more important, to time the transit to determine the Astronomical Unit.

Only six transits of Venus are known to have been observed in the history of mankind, in 1639, 1761, 1769, 1874, 1882, and the last one in 2004. If you have not noticed the pattern, they occur in pairs separated by eight years. Each pair is further separated by over 100 years. After the 2012 transit, the next one will not take place until the years 2117 and 2125. If you were born today (July 3, 2023) you would be 94 for the next transit.

The size of the solar system was one of the chief puzzles of 18th century science. Astronomers of the 18^th Century knew that six planets orbited the sun (Uranus, Neptune, and Pluto hadn’t been discovered yet), and they knew the relative spacing of those planets. Jupiter, for instance, is 5 times farther from the Sun than Earth. But how far is that … in miles? The absolute distances were unknown.

Edmond Halley was an 18th Century astronomer who discovered a way to measure the Astronomical Unit by observing and timing a Venus transit. Unfortunately, he did not live long enough to witness or confirm his idea from the 18th Century transit.

Venus was the key. Edmund Halley realized this in 1716. As seen from Earth, Venus occasionally crosses the face of the Sun. It looks like a jet-black disk slowly gliding among the Sun’s true sunspots. By noting the start- and stop-times (1^stand 4^th contacts) of the transit from widely spaced locations on Earth, Halley reasoned, astronomers could calculate the distance to Venus using the principles of parallax. The scale of the rest of the solar system would follow.

But there was a problem. Transits of Venus are rare. They come in pairs, 8 years apart, separated by approximately 120 years. Halley himself would never live to see one. An international team did try to time a Venus transit in 1761, but weather and other factors spoiled most of their data.

The extraordinary attention devoted to these transits, especially in 1761 and 1769, was due to their usefulness in determining the length of the Astronomical Unit, that is, the mean distance from Earth to the Sun. Nicolaus Copernicus, in the 15^th Century, came up with the Heliocentric model of our solar system. In this model he determined the relative distances between the planets. If the Astronomical Unit in miles could be determined, then the actual distances between the planets could also be determined. During the 18^th Century one of the most accurate methods for determining the Astronomical Unit was by observing the Venus transits.

The German astronomer, Johannes Kepler (1571-1630) was the first to successfully predict transits of both Mercury and Venus. His calculations of planetary motions enabled him to accurately predict a transit of Mercury on November 7, 1631, and a transit of Venus just a month later, on December 6^th. Sadly, Kepler died a year before these events, so he was unable to personally confirm his predictions.

In 1760 Jeremiah Dixon was commissioned by the Royal Society to go with Charles Mason (then working as a junior assistant at the Royal Observatory at Greenwich), to Bencoolen in Sumatra to observe the June 6, 1761 Venus transit. Due to contrary winds and a sea battle with the French Navy, their departure was so delayed that they ran out of time and only got as far as Cape Town, South Africa. In the year following Charles Mason’s trip to observe the transit of Venus, he and Jeremiah Dixon were commissioned to settle a border dispute among British colonies in North America. Their four-year effort resulted in a line of demarcation that formed part of the borders of Pennsylvania, Maryland, Delaware, and Virginia (now West Virginia). The demarcation is known as the Mason–Dixon Line. It has since been used metaphorically to describe the entire boundary between slave and free states during the 19th-century. After Pennsylvania abolished slavery, it served as a demarcation line for the legality of slavery.

Charles Mason, left, and Jeremiah Dixon, right, laying out the boundary that will eventually become the Mason-Dixon Line that delimited slaves states from non-slaves states leading up to the Civil War. They spent four years on this boundary following their failed attempt to observe and time the 1761 Venus transit.

The Mason-Dixon Line between Pennsylvania and Maryland.

The one astronomer who captured my attention over all the rest and, who, after my observation of the 2012 transit, I could most easily identify with, was a Frenchman whose name is such a mouthful that I cannot pronounce it: Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière. Le Gentil epitomizes indefatigability; he defined relentless determination and drive. Never have I read about a more intrepid traveler, or one who was so determined to see the 1761 transit that he was willing to undergo the rigors and hazards of travel across thousands of miles to Ponticherry, India at a most inauspicious time – Europe was embroiled in a wide ranging war that could rightly be described as a world war, but is known to history as the Seven Year’s War. If the hazards of war were not enough, politics, pestilence, and the caprice of weather conspired to prevent him from seeing the 1761 transit. Still, he did not give up. He set his sights on the 1769 transit and sailed to Manila barely surviving the stormy journey. The rest of the story is well known. He was ordered from Manila to Pondicherry where clouds obscured the transit; he had missed it again. Adding insult to injury, the transit was observed and timed in Manila by two amateur astronomers he had trained there. His indomitable will was not enough to succeed. Yet, despite all the hardship and obstacles, he never gave up.

Guillaume Joseph Hyacinthe Jean-Baptiste Le Gentil de la Galaisière.

Observing and Photographing the Transit

In a very real sense, Le Gentil’s efforts, and unwillingness to give up inspired me when I most needed it on the day of the 2012 transit. On the morning of June 5, we rode in a van to the visitor’s center at 9000 feet on the slopes of Mauna Kea. Blythe and I lugged our gear up to the top of a hill so that we would have an unobstructed view of the entire transit. A hill would block the view of the 3^rd and 4^th contacts of the transit for those who stayed at the parking lot of the visitor’s center. I did not come all the way from Indiana just to see the beginning and miss the end of the transit. Despite the lower partial pressure of oxygen at 9000 feet, we manage to get to the top of the hill without difficulty. If Le Gentil could overcome the hazards of his travels, we could climb a couple of hundred vertical feet.

The skies were crystal clear, but there was a bit of wind that worried me. To avoid as much of the wind as possible, we found a spot in the lee of a large boulder and sat about to set up my camera mount. We were on a slope but found a relatively flat piece of ground. We set the tripod up first, but quickly realized that the coarse volcanic gravel would not keep the mount steady. We fixed this problem by placing a flat rock under the three legs to spread out the weight. Three large rocks on the tripod tray firmly anchored the tripod to the ground. It seemed solid; it would have to do. Next, we had to orient the mount as close to true north as my little handheld compass would permit. I eyeballed it as best as I could. We then gingerly leveled the mount using the leveling bubble as we had practiced several times in Indiana. The bubble looked dead center. So far, so good; we were starting out well. To save time, I had attached the two drive motors to the mount the day before. I knew that my effort at perfect orientation was going to be far from perfect. I knew I would have to manipulate the up/down and right/left buttons on the motor control pad to keep the Sun centered in the viewfinder all day. I then attached the lens/camera to the mount and balanced it to my satisfaction.

With the axis level locks open, we oriented the camera at the Sun, which seemed almost directly overhead. This made it very difficult to get down far enough for me to look through the viewfinder of the camera to see the sun. But I soon found it. With the lens rolled back to about 300mm I focused the lens with auto focus, rolled it out to 500mm and put the focus on manual. I took a photo, and it seemed fine. The color of the Sun was a nice orange/yellow and as far as I could tell, it was in focus. I looked at the camera on the mount and soon realized my first error. It was oriented in such a way that toward the end of the transit the camera would hit the tripod legs and be prevented from lowering enough to get the last part of the transit. I quickly reoriented the camera to the other side, and it looked much more like I had come to expect. There was plenty of room for the camera to move the 120 degrees that was needed to get the entire transit. Again, we had plenty of time before the transit began and all seemed to be working fine. That is when things started going very wrong.

The bus took us to this visitor’s center on the slope of Mauna Kai at about 9000 feet. Most of the people with telescopes set up in the visitor center parking lot. Blythe and I elected to move up to this hill because from the parking lot a hill would obstruct the last part of the transit. I wanted to see all of it. It was a bit of a hike to get here and that is probably why most people stayed at the visitor center.

This is the spot where we set up our camera/tripod, just below this rocky hill.

When we found a spot to set up the camera/tripod we observed these clouds moving in. This was a concern, but they soon dissipated. Throughout the six-hour plus transit, the skies were clear.

This is a view of the slops of Mauna Kai from our vantage point.

These are two of the many craters on the slope of Mauna Kea.

I used rocks to shore up the one rock with the tripod leg on it. It was not the best setup, but it was all we had given the loose rock and the location on the hillside.

It is finally all set. It looks more complicated than it really is. The dangling wire is the automatic, programmable shutter release.

Notice the rocks on the plate under the center of the tripod. This was to weigh the tripod down so that the wind would not move it. This set up was a bit precarious. The rocks shifted and the least little bump might bring it crashing down. During the transit I did bump it a bit necessitating realigning the camera to get the sun back in the viewfinder.

The tripod legs are set on rocks to get it straight.

Before the transit started, we paused for a photo. You can see others with a similar set up in the background. The boots I am wearing are the same boots I wore when I fell in Scotland in 1999. They are also the boots I wore when Dave and I climbed Mt. Kilimanjaro in 1997. They have been around and are starting to fall apart. I had to tie the toe of the right sole to the rest of the boot to keep it from coming off.

This is a view from the other side. I have taken my white cap off because the bill got in the way of the camera. I paid a price for this because without the cap my forehead was exposed to the sun for six hours and I got a sunburn.

The transit has not started, but I am practicing with the motor drive buttons. During the transit the camera was pointed nearly straight up.

This is during the transit. I spent most of the six-hour plus transit with my eyes glued to the camera eyepiece to make sure the sun stayed in the viewfinder. The clock drive was to do most of the work to keep it there, but it was a rather crude setup so that I had to constantly use the motor drive buttons to keep the sun as close to the center of the viewfinder as I could.

Blythe was a big help setting up the tripod but here she relaxes taking in the stark scenery.

I took this shot before the transit started to make sure everything was working okay. There are several sunspots visible.

When I tried to take a couple more photos of the sun, to see the sunspots that would tell me I was probably focused I began to hear a very unfamiliar, and very troubling sound coming from the camera or lens. And, to my horror, I was getting an error message on the camera LED screen, and worse, I was not getting any photos at all. It had never done this before, and I could not figure out what the problem was. And time was running out; the transit was to begin in just five minutes. I thought it was the lens, but quickly switched to my old Canon D60, but got the same ominous sound emanating from the lens, and still getting the error messages. The problem had to be with the lens. Le Gentil’s curse had come to haunt me, too. It soon became apparent that the lens contacts were not touching the corresponding camera contacts. I rubbed them with a cloth, but this did not help. Blythe, keeping a cool head, tried pushing the lens onto the camera a little more forcefully. This seemed like a ridiculous idea to me, but to our great relief, it worked. My old camera began taking photos each time I pushed the button on the programmable shutter release. We had missed the 1^stand 2^nd contacts and the first ten minutes of the transit, but at least we were getting photos at the programmed rate of once every five minutes. I was very disappointed at missing the beginning, but I could live with this, it was finally working right; we would get most of the transit. For the next half hour everything worked well. The camera was taking photos at a shutter speed of 1/640 and the aperture was set at f/6.3. But, like Le Gentil, my troubles were not over.

As I expected, the mount was not tracking the sun perfectly, forcing me to keep my eye clued to the camera viewfinder and making minor adjustments with the motor drive buttons. It worked, but there was little time to relax because I had to continually fine tune the mount orientation. Despite the early problems with the lens, the contraption worked, and the programmable shutter release dutifully clicked off photos every five minutes.

This is one of over a hundred photos of the transit that clearly shows Venus over the disk of the Sun. Also, the sunspots are shown. In this view Venus moved form the 2 o’clock down to the 5 o’clock position

We got several good shots of the transit with Venus now clearly within the disk of the Sun when disaster struck again – I began to understand what poor Le Gentil must have gone through. While moving around to find a more comfortable position to sit – it was very difficult to get low enough to see the viewfinder with the camera pointing nearly straight up, and because I was sitting on volcanic gravel – I bumped the camera out of alignment with the sun. I now had to relocate the Sun, which I could only do with the lens zoomed back to 300, position the Sun within the center of the viewfinder and start it going again. When I did this, I ran into the same problem as before; the camera would not recognize that a lens was even attached to it. My frustration mounted. We were losing precious transit photo opportunities. I could not get it to work again. I got the Canon D5 out and put it back on the lens. Blythe pushed the two together again, I relocated the Sun, and to my great relief, heard that beautiful sound of the shutter opening and closing as before. We were back online.

Throughout the transit, I was aware of Venus as she made her slow, but inexorable passage across the disk of the sun. Franz had warned me to be sure and not get so caught up photographing the transit that I did not watch it. Not only did I look through the viewfinder to keep the Sun in the center, but I also watched the little black dot of Venus. It was simply beautiful. Despite the early problems with the lens, it had all been worth it to watch this dance of Venus with Apollo.

As the Sun moved toward the horizon the mount/camera dutifully followed. To my surprise, as it lowered, the mount required less manual manipulation to keep the Sun in the center of the viewfinder. As Venus neared the 3^rd contact, I had Blythe manually push the button on the shutter release every thirty seconds hoping to capture the infamous black drop effect. We kept this up until Venus disappeared after the 4^th contact. And then…it was over.

The ‘black drop effect’ occurs just after the 2nd contact and just before the 3rd contact. In this photo the ‘black drop’ occurs at the 3rd contact at the 5 o’clock position.

Just after second contact, and again just before third contact during the transit, a small black ‘black drop’ appears to connect Venus’s disc to the limb of the Sun, making it impossible to time the exact moment of second or third contact accurately. This led to the failure of the attempts during the 18th century transits of Venus to establish a truly precise value for the astronomical unit.

The ‘black drop’ effect was long thought to be due to Venus’s thick atmosphere, and indeed it was held to be the first real evidence that Venus had an atmosphere. However, it is now thought by many to be an optical effect caused by the combination of the extreme darkening of the Sun’s disk near its apparent edge and the intrinsic imperfection of the viewing apparatus.

This is a video I made of the hundred plus photos of the transit. Although not technically a good video, it clearly shows the planet Venus moving across the disk of the Sun. I was quite pleased with our photographic record of the 2012 Venus transit.

This is a short video I got from YouTube of a close up of the transit.

Epilogue

All in all, the early trouble with the lens notwithstanding, it had been a success. We had witnessed a most beautiful wonder of nature, the last Venus transit of this century. As we packed the gear and began to descend the hill to the waiting van to take us back to the hotel, I thought back to the hapless Le Gentil. He had had his own troubles and travails and never did get to see the 18^th Century transits. But, for Blythe and me, on June 5, 2012, the goddess Fortuna looked down upon us and smiled.

The next Venus transit is December 10, 2117. Get ready!