Observing the transit of Venus across the Sun using a telescope

Thijs de Haas

There is this warning in the manual of my Meade telescope: Never use a MeadeETX AstroTelescope to look at the Sun! Looking at or near the Sun will cause instant and irreversible damage to your eye.

So I was pleasantly surprised when I came across the article by Rich Fienberg – ‘Build a sun funnel: A safe way to use a telescope to observe the sun using rear-screen projection’. The article described how to use a Blitz Super Funnel to support the projection screen and if I combined this with the calculations for which eyepiece to use (details of calculations can be found here http://transitofvenus.nl/wp/observing/build-a-sun-funnel/ ) I could hopefully use my telescope to view the transit!

Of course I had no quick access to a ‘Blitz Super Funnel’ but I really liked the idea, so instead of a funnel I used a round biscuit tin (diameter 11 cm and height 15 cm). In the center of the bottom of the tin I managed to make a round hole of 32 mm. In this hole I glued (with epoxy) a 6 cm long piece of PVC drain pipe, outer diameter 32 mm, inner diameter 30 mm. This piece of drain pipe made a sliding fit with the rubber top of my telescope with the 25mm focus. I removed the cover of the biscuit tin and replaced it with a round piece of translucent plastic, which was the projection screen.

It was also really important to protect the telescope itself from sun damage, so I reduced the aperture of the front lens – an easy step, I just covered the lens with a piece of black paper with a small circular hole of 3 cm diameter.

And it all worked perfectly, the biscuit tin sun funnel allowed us to observe the transit of Venus on the 6th of June 2012!

The transit of Venus across the Sun

Matthijs P. de Haas , Floda31, Sweden, 6 June 2012

I did a presentation on the eve of the transit where I discussed the three astronomers that were essential to the prediction of the Transit of Venus across the Sun, almost 400 years ago:

- Tycho Brahe, who spent his life and his enormous wealth to accurately record the positions of the planets.

- Johannes Kepler, who used Brahe’s data to the present a new model of our solar system

- Galileo Galilei, who showed, using his telescope, the phases of Venus. In his book Sidereus Nuncius (Starry Messenger) he proved to the world the validity of the heliocentric model. However the church was not amused: Galilei was found guilty of heresy; his book was banned and he was placed under house arrest for the rest of his life.

These three famous astronomers were recently in the news again:

Pope John Paul II reopened the Galileo case in 1979, and in 1992 finally reversed the sentence against him.

Historians are also still trying to piece together the whole picture of what happened in 1601: did Kepler killed Brahe? was Brahe was the father of King Christian IV? (Was the King Christian IV of Denmark an illegitimate child?) and did William Shakespeare write a truthful crime story about the State of Denmark in his play “Hamlet”?

Dr Suzanne Aigrain, our trip exoplaneteer usually based at the University of Oxford, shared her thoughts on the transit adventure on the exoclimes.com blog, we have reposted her thoughts, here is her last post:

It’s 2pm on the day after the transit, and I’m a little bleary-eyed. It was a long night, but it was worth it. I wasn’t so positive at 4.30am, three quarters of the way into the transit. A band of blue to the South-West had taunted us all night, but the Eastern sky remained determinedly cloudy, and the NASA webcast was as close as we thought we’d get to the transit. But then, very gradually, the skies parted, and we saw it!

But first things first. A few of us, brave or foolish, started the day with a run and a swim in a nearby lake, the iron-rich water a deep brown red – and icy cold. Then it was back to Floda for a round of brief introductions of everyone’s projects – too many to list them all here, but a few ideas appear again and again. One is the way in which the transit highlighs the passage of time, another the contrast between the sub-arctic landscape and the almost graphic nature of the event itself. And then there is the potentially recursive exploration of the way in which we observe the transit, record it, and then look at the images we made.

Lunchtime found us in the workshop, making final adjustments to our viewing preparations:

and putting the finishing touches to the monument/viewing platform, including the critical window, which is not – as I previously thought – welder’s glass, but solar viewing film stretched between two glass panes. Much of the afernoon was dedicated to the preparation of a group performance, just before the start of the transit, in the form of a procession structured around the orbits of the solar system planets, but also incorporating notions of orbital migration and planet-planet interactions, which had come up in dicussions of how our theories of planet formation have been affected by the discovery of exoplanets.

After dinner, while waiting for the transit to start, we were treated to a wonderful talk by Thijs, on the work and lives of three astronomers who played key roles in changing our conception of the solar system: Brahe, Kepler and Galileo. I’d never noticed the parallels between Brahe’s life and Shakespeare’s Hamlet, but they are very striking. It was also fascinating to learn how Kepler, who briefly worked for Brahe before the latter’s death, made off with all the data Brahe had accumulated over twenty years of intensive and painstaking observations, before Brahe’s heirs thought to stop him. During his lifetime, Brahe didn’t trust Kepler, he wholeheartedly rejected the notion that planetary orbits were ellipses, and only allowed Kepler to access a very small portion of his observations. Had he not died then, Kepler might never have had the data he needed to conceive and demonstrate his famous laws.

After that I stepped in with a brief introduction to how what we knew of the solar system shaped our theories of planet formation before we started to discover exoplanets, but we soon switched over to the NASA webcast to see the start of the transit – which occured while the Sun was below the horizon in Sweden. Suitably stoked up by the enthusiasm of the webcast commentators, we headed out to the field in front of the monument, for the procession, timed to end just as the Sun would rise. The participants held torches and lit beacons symbolising the Sun and giant planets, and then fanned out to follow densely packed orbits, each close encounter leading to a brief interaction and a change of orbit. Accompanied by singing and drumbeat, it was both fun and moving, and I am eagerly waiting to see footage of it taken by intrepid climber Hugo from the top of the radio mast, which supplies Floda with a much faster internet connection than I have at home in Oxfordshire.

There followed tense hours of waiting by the campfire for the sky to clear…

…until, at last, the Sun began to show dimly though the clouds.

We rushed to the telescopes, and at first all anyone could make out was a fuzzy solar disk through the mylar window – it wasn’t strong enough to cast a projected image. A few of us thought they saw Venus through the binoculars, but the image was so blurred by clouds it was hard to be sure. And then, gradually, shadows began to appear on the ground and we could align and focus the telescopes, and there it was! Below is a picture of Abby pointing out Venus on my sun-funnel for Otto, the 7-month old son of Rich and Marije (who run Floda31):

… and here is a photo of Thijs’s home-made projection device, designed to give a smaller but brighter image:

The entire population of Floda – all twelve of them – came out to join us…

… and it was a merry 45 mins, as everyone got a good look, cameras clicked and rolled, and there was much whooping and ahing.

Dr Suzanne Aigrain, our trip exoplaneteer usually based at the University of Oxford, shared her thoughts on the transit adventure on the exoclimes.com blog, we have reposted her thoughts, here is the fourth of five posts:

I arrived at Umea airport around 4pm, where I met up with the other stragglers – most of the other participants arrived last night or this morning. Abby picked us up and took us straight to Umevatoriet, which is as much a public science education centre as an observatory. There we were given a chance to look at the Sun in Halpha (though it clouded up by the time I got there), treated to a truly excellent planetarium show, and given a chance to weigh ourselves on Mars, Venus, and the Sun:

We also tested our mental skills in the centre’s current exhibition of Arabic mathematical puzzles (complete with desert setting) and I got a chance to meet up with Bastien and try out the mount he kindly offered to lend me – which works like a dream.

After a supermarket stop to stock up, we headed off into the wilderness – an hour’s drive on empty roads through trees, lakes, and more trees, passing the occasional red wooden house … and a pair or rather flegmatic moose. The site is a wide open field, with a number of small wooden cabins and outbuildings, in which we are staying, dotted around the outside, and beyond… forest, as far as the eye can see. It’s 00.30 am, and just bright enough to read outside.

There are several people out in the field with tripods doing a much better job than I of capturing the spectacular moon on camera. Everyone is by the bonfire, trying to keep warm whilst getting to know everyone else, and enjoying the peace and quiet. On the practical side: compost toilet, outdoor bath (heated by a woodstove), and barbecued Swedish meatballs. What more could you ask for?

Now all we need is clear weather. Tonight it’s cold but only a little hazy, but the forecast for the next few days is uncertain. On the programme tomorrow: morning swim (!) in the nearby lake, work on completion of the Venus transit monument, and a few talks – including one Thijs de Haas, a retired physicist who is the father of one of the owners, on the history of the Venus transits, and one by me on its implications for modern science.

Feature Image: Scale calibrated to weights on Mars, from a sicence exhibit at the Umevatoriet observatory. [Photo Suzanne Aigrain].

Dr Suzanne Aigrain, our trip exoplaneteer usually based at the University of Oxford, shared her thoughts on the transit adventure on the exoclimes.com blog, we have reposted her thoughts, here is the third of five posts:

What do you need for a short trip to Sweden? Thermals (I’m told it’s unseasonably cold out there at the moment), passport … and of course, a telescope and a plastic funnel.

The FLODA31 team have not been idle in the run up to our arrival: they have teamed up with the local architecture school to build a dedicated viewing platform. This is what the design looks like:

The two cirles are inspired by the orbits of Venus and the Earth, highlighting (and somewhat exagerating, of course) the difference in their orbital inclinations which makes the transits of Venus as seen from the Earth such rare events. The Sun will rise at one end of the elongated window, and will gradually edge across it as the transit unfolds. The window will be made of welders #14 glass, so onlookers can watch the spectacle safely.

Abby and Chris from super/collider, who are organising the trip, got there last week and got stuck in too, and as of yesterday (June 2), the Earth’s orbit was almost complete:

Most of the people coming from the UK will arrive at Umea on Monday afternoon. After a brief visit to Umevatoriet Observatory, who are also involved in preparations for the transit viewing, we’ll drive the final two hours to the tiny hamlet of Floda.

I am really looking forward to seeing the purpose-built viewing platform for myself, I think it will frame the transit in a spectacular way. But Venus will still appear quite tiny on the solar disk – at the limit of what can be discerned by eye – so it will also be good to have a magnified view. Chris will have a pair of binoculars on a tripod, as well as a small telescope, both of which he will equip for Sun-watching by covering their entrance apertures with solar viewing film.

To complement this, I decided to build a sun funnel, which attaches to the eyepiece of a small telescope, allowing several people to enjoy the view at once, as in the example below:

By the beginning of last week, I had all the ingredients:

… though the funnel had to come all the way from the US: apparently no-one sells black funnels of this particular shape in the UK. The company that sells them in the US wouldn’t deliver abroad… but luckily my colleague Fraser Clarke happened to have an observing run at Palomar Observatory in early May, so I got it delivered there and he kindly brought it back for me. Sourcing the rear-projection fabric was a bit epic too. I only needed a foot square, but the minimum amount I could order was 3 x 1.2m… so when I get back I’ll have to figure out what to do with the leftovers. Suggestions welcome!

Figuring out what telescope to use was a little epic too. Refracting telescopes are preferrable because of the amount of light a reflecing telescope would focus onto the eyepiece when trained on the Sun. Also, you really want a motorized mount: tracking the Sun manually for several hours could get tedious. The Oxford Physics teaching course had a nice Meade ETX-125 they were willing to lend me. However, the case for it was too big to take on the plane as hand luggage, and it is rather too fragile to go in the hold. So I thought I would buy a smaller, portable but still motorised telescope, such as the ETX-70 Backpack – this would be quite a nice thing to have when going camping anyway. But I was warned the fixings which hold the optics in place are made of plastic, so there would be a high risk of melting them when pointing the telescope at the Sun… no go.

Fraser came to the rescue and suggested I use the star-finder of the Philip Wetton telescope - the 11″ telescope we normally use for undergraduate projects in Oxford.

We tried it, and it works really nicely, giving a lovely view of a couple of active regions. It also fits into a smaller case that I should be allowed to take as hand luggage. Only one small hitch: it has no mount of its own, and we couldn’t find a spare motorized mount.

At this stage, I asked Abby if she knew anyone who could help locally – and finally I think we have a solution. Bastien from Umevatoriet Observatory very kindly spent a few hours equipping an equatorial mount they had lying around with a motorized drive. Now we only have to hope that we can attach the finder scope to it… I’ll find out tomorrow.

The weather forecast for the next few days is not perfect, but it is a lot better in Northern Sweden than in the UK, so I’m quietly optimistic.

(photo credit: Venus transit 2004, from Vol. 3: Truth Study Center © Wolfgang Tillmans)

Dr Suzanne Aigrain, our trip exoplaneteer usually based at the University of Oxford, shared her thoughts on the transit adventure on the exoclimes.com blog, we have reposted her thoughts, here is the second of five posts:

Edmund Halley famously said: “This sight […] is by far the noblest astronomy affords.” Had he had access to modern telescopes and instruments, he might have reserved this accolade for another astronomical vision. After all, seeing a small black dot cross a big bright disk, very slowly, might not sound like much. But anyone can observe the transit, with basic precautions and minimal equipment, and it brings home the mechanics of the solar system in an immediate way, as captured in the photograph of the 2004 transit by Turner-prize winning photographer Wolfgang Tillmans. For someone like me, who spends their entire professional life searching for and studying planetary transits, the symbolic significance of the event is all the more obvious, and I’m looking forward to watching how it inspires the other participants of the expedition, and to helping them observe and understand it.

But symbolism isn’t all there is to it. Observations of the transit of Venus have been important historically in a number of ways. The duration of the transit was used to measure the scale of the solar system, starting with the first documented observation by Jeremiah Horrocks in 1639, with consecutive refinements up until the beginning of the 20th century, when other more precise techniques were developped. It is also by observing a transit of Venus in 1761 that the Russian astronomer Mikhail Lomonosov first discovered that Venus, like the Earth, had an atmosphere. During the early part of the transit, he noticed a bright ring around the part of Venus that was not yet super-imposed on the Sun, and correctly supposed that it must be due to refraction of the Sun’s rays by the atmosphere. Ironically, though, the first real evidence that Venus had an atmosphere was long held to be the “black-drop effect” – which marred attempts to time the start and end of the 1769 transits precisely. It turns out that the black-drop effect is purely instrumental – it is caused by diffraction and other aberrations in the telescopes used, and completely disappeared in observations of the 2004 transit made with more powerful telescopes. Lomonosovs’ discovery, though, was based on a different effect, and has stood the test of time. This re-interpretation of the black-drop effect is somewhat reminescent of recent (even ongoing) debates surrounding exoplanet observations, where disentangling atmospheric and instrumental effects is often very difficult.

 I was finishing my PhD when the last transit occurred in 2004, and I remember anxiously running the transit detection algorithms, which were the mainstay of my thesis, on measurements of the Sun’s total brightness taken by the SoHO satellite in the month around the transit. Would I be able to see it, despite all the other variability caused by sunspots and such like? The answer was yes – but only if I knew where to look first. Nonetheless, more serious analyses of the signature of the 2004 transit in similar data helped establish confidence in the transit-search missions like CoRoT and Kepler, which were then in the late stages of their preparation. Kepler is now discovering terrestrial planets by the bucket-load, and spectrally resolved transit observations are routinely being used to probe the atmospheres of larger exoplanets. The 2012 transit offers an opportunity to test and calibrate this type of observation on a planet whose atmosphere is much better known. Indeed, the Hubble Space telescope itself will observe the transit, although of course it will not point at the Sun directly. Instead, it will point at the Moon, in an attempt to measure the how the spectrum of moonlight – namely sunlight reflected by the Moon – will change during the transit. This will be a difficult measurement – the wavelength dependence of the transit will be very small, as Venus’s atmosphere covers only a very small fraction of the solar disk – but at least there will be no shortage of photons.

The coming month will also be a busy time for exoplanet transits with Hubble, with observations scheduled on June 8th and June 10th as part of our large programme on transit spectra for hot Jupiters in the visible. In my next post I will describe my own plans for observing the transit – more Heath Robinson than state-of-the-art, I’m afraid…

3

Dr Suzanne Aigrain, our trip exoplaneteer usually based at the University of Oxford, shared her thoughts on the transit adventure on the exoclimes.com blog, we have reposted her thoughts, here is the first of five posts:

Next week, on June 5/6 (depending on where you are) Venus will transit across the disk of the Sun for the second – and last – time in our lives, and I am heading North to watch it. I’ll be taking part in an unusual kind of expedition: most of the other participants will be artists – illustrators, photographers, film-makers, graphic designers, even a choreographer. The trip is being organised by super/collider, a London-based collective which promotes interaction between science and the creative industries. Our base will be FLODA31, a laboratory for innovation and creativity established on the site of a former farm in one of the last remaining wildernesses of Europe, a few hours North-West of Umeå. At this latitude and time of year, the Sun barely sets at all, so – provided the sky is clear – most of the transit will be visible.

All going well, I’ll be posting regularly in the build up to and during the trip, so watch this space! And in the meantime, if you want to find out more about the transit, listen to the Frontiers program at 9pm today May 30th on BBC radio 4.
Suzanne Aigrain, Oxford

The night of the transit was intense, we watched the disc of Venus first moving across the Sun on a live webcast from Hawaii with lots of cheesy american commentary, a very bizarre addition out in the Swedish wilderness. About 1am we headed outside for our own viewing experience and to welcome in the heavenly body of venus to our sunlit skies. Commencing with a series of beacons that were sited the correct distance (proportionally) away from the sun – located at the centre of the Venutian monument. The distant icey planets of our solar system were announced by piercing howls from deep in the forest, heard echoing around the hills. As we approached closer to the sun the giant hot planets were small fires lit across the landscape leading to where Earth and Venus aligned with the Sun in the central monument.

This signalled the start of the procession – a mixture of science, pagan ritual, Greek myth, plus some wild costumes. It was an exhilarating experience for all and surely the skies heard us, as magically the clouds parted a few hours later and we saw the silhouette of Venus in all her glory.

Here are two different accounts of the ceremony:

Finbar Mostyn-Williams (director of ceremony)

“Who was she who made love to you
in your dream, while you slept?

Where do the the things in dreams go?
Do they pass to the dreams of others?

And does the father who lives in your dreams
die again when you awaken?

In dream, do plants blossom
and their solemn fruit ripen?”

Pablo Neruda

Science fascinates me because in many ways it has been able to change perception from something that is solely anthropocentric to something that is driven by more abstract logic and rules. So a classic question of skepticism was, “How do we know if the Sun will rise tomorrow morning?” This has been challenged by our scientific understanding of planetary orbit and perhaps rendered redundant (although not totally). Even so, as human beings there is an immediacy to the way that we experience events which lies beyond reasoning. This is simply how the events register with us visually or experientially before we combine them with additional reasoning to give them logic. So it is interesting for me that while we might be able to reason something like the transit of Venus as the orbiting of planets around a star, we experience it as something more mystical: It is a deformation of the Sun; an abnormality and inconstancy with what we experience on a daily basis. We interpret it as a sign, we reference the Goddess of Love, the Sun, the Giver of Life, and imagine that there might be a message from a above that we should receive and take heed of.

Forgetting then, our knowledge of the Sun as a star and Venus as a planet, I was affected by the transitory emblazoning of Venus on the Sun. It reminded me of how we deal with memories, often searching to replicate times that once were which called to mind Orpheus and Eurydice. I loved the fact that Venus would pass over the Sun and seem like it was touching but in fact it never would. I loved the fact that our experience of the event could not be replicated because this was the last time the passing would happen in our lifetime. Phenomenologically therefore, there would be no way of proving the event, it would merely be something that we would have to trust as having happened. We could also not replicate the emotions we felt during the passing, we could possess them and reference them but they would no longer exist except in our minds. Orpheus goes to the underworld to find Eurydice, but she is a spectral figure who fades when he looks at her. Eurydice has been fixed in time. She is replicable only as a memory; Orpheus can summon the past, but he cannot recreate the present. So in the ceremony we wanted to show skeletons (the willows), souls (the fire), gravity (represented by the concentric circles), free-will (each individual being able to move as they wished), determinism ( limitations of the circles and the rules of people not being able to pass each other), human relations (the fact that people would meet or follow), anima mundi paganism (the breathing and singing), creation (the planting of the torches), mortality (the fires going out), dreams (the smoke that remained) and individual and collective consciousness (us breathing and feeling together, leaving and following our own paths but then forming part of a whole at the end in which each part complimented the other).

Suzanne Aigrain (observer):

Much of the afernoon was dedicated to the preparation of a group performance, just before the start of the transit, in the form of a procession structured around the orbits of the solar system planets, but also incorporating notions of orbital migration and planet-planet interactions, which had come up in dicussions of how our theories of planet formation have been affected by the discovery of exoplanets.

The procession was timed to end just as the Sun would rise. The participants held torches and lit beacons symbolising the Sun and giant planets, and then fanned out to follow densely packed orbits, each close encounter leading to a brief interaction and a change of orbit. Accompanied by singing and drumbeat, it was both fun and moving.

Natalie Wills is an architect who is interested in how people understand spaces on the urban scale. she believes that maps are not always about geography, and is interested in how people build “mental maps” in their mind based on memories, snapshots and the perception of spaces. during the transit she encouraged visitors to draw a map of their experience, documenting Floda in a unique and personal way in an effort to give a group identity to the Transit of Venus and the journey they went through to watch it