How Cook navigated to Tahiti

A sextant built by the English instrument maker Matthew Berge. Courtesy Powerhouse Museum

I have received a letter from Jonathan Milne-Fowler, Lieutenant-Commander RANR (Retired) regarding my book Transit of Venus: 1631 to the present. He says, ‘I’ve just finished reading the book on the Transit of Venus and found it well written and informative. That said I did find a couple of points on which I take issue and have written a commentary’. The two points both refer to Captain Cook’s first voyage that was mainly to view the 1769 transit of Venus from Tahiti. Here I just quote his commentary regarding Cook’s navigation and leave the section on the shape of Cook’s ship the Endeavour to another time.

Determining longitude: A commentary by Jonathan Milne-Fowler, Lieutenant-Commander RANR  (Retired)

At page 48 of this book the statement is made that Captain James Cook on his first and most famous voyage (1768-1771), using the method of lunar distances to determine longitude, became the first navigator to know his position at all times. This assertion has been made by other authors but it is erroneous.

There is no doubt that James Cook was one of the few navigators at that time capable of performing the complicated calculations required to determine longitude at sea, but this was always subject to the vagaries of the weather allowing the necessary observations to be made. A bank of fog or cloud in the wrong direction, obscuring the horizon or the sun, moon or stars, may frequently frustrate the intentions of navigators intending to obtain a set of observations for the purpose of determining the position of their ship at sea. More than one hundred years after Captain Cook’s voyages ships supplied with chronometers still came to grief because masters had been unable to take sights needed to calculate latitude and longitude.

Among the first navigators able to determine their position at all times were those embarked in Trident submarines equipped with inertial navigation systems. GPS systems now enable navigators to determine their position with a degree of accuracy which was unimaginable to the likes of Captain Cook.

Lieutenant Commander Milne-Fowler is, of course, correct that saying that Cook knew ‘his position at all times’ is a little exaggerated for he could not make observations during times of bad weather. However, as he was the first to utilise the newly developed method of lunar distances to find the longitude of his ship, he had a better idea of his position than any previous navigator on a major voyage of exploration.

When those previous navigators were sailing to an island they would sail well to its east (or west), sail down a longitude line to the right latitude and then sail west (or east) until they found it. If they had estimated incorrectly and they were on the other side of the island to what they had thought, they would be sailing away and in trouble. In contrast, Cook could sail directly to the location he wanted.

The method he was using to find longitude was the method of lunar distances or lunars. To facilitate the use of this method Cook had with him on his ship the Endeavour Nautical Almanacs, newly published by the Astronomer Royal Nevil Maskelyne. These almanacs listed the angular distance of bright stars from the edge of the Moon at various times at Greenwich.

Cook and subsequent navigators using this method measured the angular distance between a star and the Moon with a sextant together with the elevation of the star and the Moon above the horizon. What made the technique difficult to use was that calculation had to be used to make the measured distance comparable with the tabulated distances.

First the navigator had to make the obvious corrections for the distance between the edge of the Moon and its centre and for the zero or index error of the sextant. Then came the tedious business of ‘clearing the distance’, which was applying corrections for parallax, that is working out what the measured lunar distance would have been if made from the centre of the Earth, and correcting for refraction, the shifts in the positions of the Moon and the star due to the bending of their light by the Earth’s atmosphere.

On his second and third voyages Cook had the benefit of the newly developed chronometers, but on his first voyage Cook’s excellent charts of Tahiti, New Zealand and the east coast of Australia were all due to his skill with lunar distances. He may not have known his position at all times, but he knew it when it mattered.

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Full-dome shows underway

Planetarium program poster

The Bays Mountain Planetarium in Kingsport, TN, is currently producing an interactive show about the transit of Venus, with distribution scheduled to begin at the end of February. Planetarium Director Adam Thanz writes,

Viewers will learn about eclipses, the transit, the main characters of the event (the sun and Venus), and also focuses on a key point in Venus transit history with the voyage of Captain Cook on the Endeavor. The show includes live, interactive activities that let visitors practice and understand important aspects of transit history.

Length of show is not yet etched in stone, as it is still in production, but it will be around the half-hour mark. A segment at the end allows each theater to personalize the show with what to expect locally, viewing times and observing sessions. This show has been financially supported by the Bays Mountain Park Association.

Meanwhile, another all-dome video is nearing the distribution phase in early February. The Transit of Venus, for which a trailer is online, will be a shorter four-minute introduction to the celestial phenomenon and its significance, past and future.

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We’re historical re-enactors

The Eros Parallax Project has now ended: the analysis of the results can now start. If you still have some pictures of Eros, don’t hesitate to submit your data. If you weren’t able to picture Eros, but are still curious to see what others managed to photograph, just go over to our depository of images, and see if you can do some astrometry yourself. Below is an example, taken by Alexander Kostin from Houston, Texas on January 28.

In an interview for space.com Michael Richmond made a wonderful comparison between our Eros Parallax Project and other recreations of historical events:

Richmond calls van Roode’s project “an opportunity for students and amateur astronomers to recreate what was, 80 years ago, an important step in solar system research.”

Although modern radar provides more-accurate data, Richmond stresses that the point of the project is that students and astronomers can measure the size of the solar system for themselves.

“It’s like people who recreate Civil War battles,” he said. “They’re not teaching historians about the battle, but they’re having a lot of fun, and they’re learning something … for their own sake.”

And there’s something to be said about sharing a connection for the skywatcher pioneers of yesteryear, Richmond added.

“We’re historical re-enactors of astronomy.”

And the same is true for the transit of Venus: by repeating the observations made by astronomers from the eighteenth and nineteenth century, students and amateur astronomers can experience the scientific endeavours of the past first hand, almost getting in touch with the historical figures who put their lives at stake for the advancement of astronomy. And someday in the future, millions will look back at our projects as well while preparing for their pair of transits of Venus.

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An educational event

(Credit Andrew Giddings)

The reason we created the Venus Transit Expedition was to share this amazing event with the world, as a new vehicle for showing how wonderful the world of science can be. I’ve definitely spent my fair share of time with people over my short time so far here on this little blue rock. What I’ve noticed about people in general mostly, is that general people are different. I’ve also noticed that some things change, and some things don’t. These two ideas underpin what I do for a living.

On a day to day basis, I travel the country and the world talking on topics as varied as science, sport, geography, engineering and all the stuff in between. I show people the science of extreme sports, the wonders of the universe, and the grandeur of adventure. What I mainly do is create vessles designed to break down the perceived barriers between the public and complex ideas, such as the transit. To do this, you have to remember that people are different, and things have changed.

One thing that definitely hasn’t changed, on the whole, are the schools (some countries definitely have progressed more than others). We could definitely dwell on the current education systems and talk of their unbelievable linearity, how children are put in to the process at one end, follow a linear path and come out at the other end of the factory line, designed to be good at preset subjects that are deemed to be important. Or we could look at the an-aesthetically created class room environments that come from an education system that demands it’s teachers follow a pre ordained curriculum through the day and mark exercise books in the night. I know plenty of teachers that really want to create stimulating, engaging material for their students, but the fact is they just don’t have time to create the hook and the content to put in to their lessons plans. But this is where the Venus Transit comes in.

If expeditions are anything, it’s exciting. Scott’s trip to the South Pole, Darwin’s voyage across the world, Cook’s expedition to Tahiti, all exciting adventures in themselves but also extremely educational with great content. Expeditions like these are great hooks for learning, if used correctly, they can be a platform from which to share a wealth of knowledge, with anyone, about anything! And that’s the key point, if we use them correctly. We have to remember that times of changed, if it’s students we’re going for, we can’t just teach them in the way we were taught, if it’s the public we’re focusing on, we can’t expect them to learn in the same way we learn.

Maybe then a multiplatform aggregate of rich varied content is the way forward? An array of cross media content that comes in many different learning packets. If we stick to the idea that people are different, then we have to provide content in all the different forms they would learn in. All too often we ask children to sit down and focus, but as Sir Ken Robinson so eloquently put recently, how can we expect them to not get distracted when there is such a wide abundance of information and stimuli out there for them? I know I constantly get distracted by social media like Twitter and Facebook and amazing sites such as Vimeo, YouTube and Tumblr. I still learn an awful lot from talking to people and absorbing information through human to human interactions, but the rest of it comes through my iPad, Laptop or mobile. It just seems we still think that if it doesn’t come from a book or out of the mouth of a professor, it’s not learning.

(Credit Andrew Giddings)

I honestly believe that everything we see and do enriches our life in some way. For me, one of the best things we can do as adventurers or Astronomers is share the Venus Transit with the rest of the world, especially as it’s such a localized event. And it just so happens, there’s a plethora of ways to do just that. Social Network sites are a dime a dozen nowadays, all offering different ways to share your content. Many of these sites are ready built for sharing content. The very ethos of sites like Facebook and Twitter are designed so that the content becomes interesting because of people liking or sharing it, it gives an essence of word of mouth to information in digital form. Video sharing sites have been under a boom too, with a number you’ll have never hear of right up to the best and most familiar like YouTube and Vimeo. However, alongside the regular content sharing sites, there are a whole load of newcomers! Sites like Ipadio are making real headway into creating almost instant content that can be created and streamed to your website in audio or video form. But also the types of content we can now upload is changing. It’s because of companies like Apple that we can now create content and data that is viewable and consumable not just by scientists anymore, but by the general public too. We can now create content and data in the field, that can be shown in its raw form to the public back home.

If you want to share an event like the Venus Transit with the public, it has to be simple and straight forward. But if you love to pass on knowledge, if you love to communicate with people, if you love to share your experience, then come follow our expedition. Of course you can come like us at our Facebook page, follow us on Twitter and find out more at the WebsiteGet in touch with us if you’d like to sponsor us or get involved in any way!

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The diurnal parallax of Eros

Our Eros Parallax Project relies on the collaboration of two observers far apart from each other making a picture of Eros at the very same time. The position of Eros on these pictures with respect to the background stars will be a little different because of parallax. Together with the geographical locations of the observers this difference yields the distance to Eros in kilometres.

Steve Duncan from Devon, Newton Abbot, UK, is conducting another interesting project on his own. He takes two pictures of Eros, some time apart. As the earth turns in the time between the two pictures, Steve is looking at Eros from two different angles. This causes Eros to appear at different positions on his pictures as well, called the diurnal parallax. Measuring the difference and deriving the distance he has travelled in space in between the two exposures, Steve is also able to find the distance to Eros. The drawback of this diurnal parallax method is that one should take into account the rapid motion of Eros across the sky.

You can follow Steve’s activity on his live journal.

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Share your Eros experiences

The Eros Parallax Project is now half way, and results are coming in. You can check these out on this results page. You can use these data to find the distance to Eros yourself using the Excel sheet prepared by Udo Backhaus. We could still use some more concurrent data with long base lines though, so if you have any chance to picture Eros tonight, please do! I would like to encourage observers especially from the southern hemisphere, where Eros is comfortably high in the sky, to take a shot. Meanwhile, we enjoy to hear from you, letting us know about your experiences and results. You can email us, send your pictures to our depository (even if the astrometry didn’t work out) or, like Francis Walsh, put together a video:

We are happy to have provided you this birthday gift, Francis!

The Virtual Telescope, a remotely controlled telescope based at Bellatrix Astronomical Observatory in Ceccano, Italy, has made a wonderful timelapse of Eros moving across the sky:

Another noteworthy observation was made by Swedish students Albin Walldén and Max Nordin of the Finnvedens gymnasium in Värnamo. They controlled the robotic 35-cm telescope of the Tycho Brahe Observatory in Oxie from the comfort of their own home. Albin and Max do not only intend to submit their pictures to the Eros Parallax Project, but made a great timelapse too.

What’s your news? Let us know at info@transitofvenus.nl!

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New video about 2012 transit

A new video about the transit of Venus by hilaroad.com was released on January 25:

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Where to look for Eros

Today, Eros reaches its shortest distance to Earth. We have to wait another 44 years until the asteroid will come this close to our planet again, in January 2056. So, it’s worth to have a look at this piece of rock measuring only 33 km. Although Eros is now so bright, it shows up even in a pair of small binoculars, it looks just like any other star, making it hard to recognise if you are not familiar with the patterns of the fixed stars. Even experienced star gazers may find this a challenge, as Eros is now in the inconspicuous constellation of Sextans. Here’s a guide to find Eros.

First, you need to know where to look. The two images below show the heavens at midnight for an observer on the northern hemisphere (left) looking towards the south-east and for an observer on the southern hemisphere (right) looking towards the north-east. Click the images for a larger view.

Follow the direction of the two front stars of the Lion’s body (η Leo and Regulus) towards the south. Sextans is then in between Mars and α Hya. If you located Sextans, the next step is to become familiar with the star pattern of the constellation. Looking through binoculars, see if you can match some stars
from the detailed finder chart. Your star-hop to Eros could start at β Sex, a star of magnitude 5. From there, pan south to δ Sex, then moving towards the south-east in an arc to find the three stars forming a triangle (at the February 1 position of Eros on the chart).

Now that you are looking at the star field where Eros should be, make sure to identify a star that isn’t on the chart and is a little brighter than its surrounding stars. That’s Eros! Keeping a close look at the asteroid, you should be able to notice its changing position after an hour or two.

If you have never done something like this, finding Eros is a great exercise in star hopping. Once you become familiar with the star patterns on the path of Eros, they will lead you as trustful friends to this unique view, night after night! Getting Eros in your field of view will certainly be an experience you will cherish for a lifetime (at least until 2056!).
 

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Art for the guild

St. Michaels Church front

St. Michael's Church in Hoole, Lancashire, UK

David Henckel of Preston, Lancashire (UK), is researching the transit of Venus from the artist’s perspective for an event near the epicenter of transit of Venus history. Henckel has been commissioned to create artwork for the 2012 Preston Guild, a centuries-old celebration which takes place once every 20 years. As he prepares for the historic guild program, Henckel is tapping into the prominent background of nearby Much Hoole, where Jeremiah Horrocks first recorded a transit of Venus in 1639.

Horrocks clock tower

Horrocks clock tower celebrates 220 years

Recently Henckel visited St. Michael’s Church, which is adorned with tributes to Horrock’s achievements, such as stained glass windows, a memorial tablet, a bell tower, a sundial, and a chapel. After a guided tour with church warden Eric Barker, Henckel writes, “they are collecting money for a flag and a windvane so that there is an outward symbol that signifies the importance of Horrocks’ observations.” St. Michael’s is an attractive little church that wears her Horrocks features like a well-deserving veteran honored with medals.  She merits a 2012 signature.

In Certain Places, the organization sponsoring Henckel, notes he and four other artists were selected “due to their collective track record of producing engaging artworks, which provide unique insights into the nature of place and community.” Henckel bills himself as a “multdisciplinary artist interested in revealing unintentionally collaborative activity,” exemplified by his recent work in translating the distribution of chewing gum stuck in paving slabs into a musical composition.

Artists selected for the Preston Guild are encouraged to interact with the public during the formative stages of the project. After a conversation with Henckel, I very much look forward to his transit of Venus handiwork, which transit of Venus voyeurs can watch as it progresses on his project blog.

I value the insight artists bring to the transit of Venus experience, and I look forward to new, innovative works from the 2012 perspective. A call for art seeks entries for an exhibit to be displayed around Michiana, the area near the Michigan-Indiana border, as part of the TROVE community celebration.

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Bright, variable Eros

While asteroid Eros is making its very close approach to Earth, it will also peak in brightness. With a magnitude of +8.5 you won’t be able to see it with the naked eye, but looking through simple binoculars will already bring the minor planet in view. Not only does Eros become brighter these days, its luminosity also varies because of its rotation and elongated shape. Christoph Gerber of the University of Heidelberg, Germany, took the opportunity to map Eros’ lightcurve during a clear night on January 26.

Equipped with a pair of 12×60 binoculars I was readably able to follow the change of brightness – all along the 5:16 hours period of rotation (00:25 to 05:55). Every half hour I made an estimate of the brightness, the program Stellarium (0.10.2) being of great help for the determination of the brightness. The expected double curve with two different maxima and minima appeared very clear. The total amplitude that night was 0.55 magnitude (7.95–8.50) – significantly lower than the possible maximum of 1.5 magnitude, but yet very conspicuous and easy to follow. The “wakeful” night has fully paid off!

Another wonderful experiment you could conduct during the nights you are already making pictures of Eros for the Eros Parallax Project!

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