Eros Parallax Project kicks off

Posted on January 27, 2012 by Steven van Roode

Tonight, many amateur astronomers and school classes are eagerly awaiting to see the asteroid Eros, now at its closest to Earth, rise into the night sky. From January 28 to February 3 they will take an image of Eros on each night, either through a telescope or with a telephoto lens, at designated times depending on their location. Photographs of Eros submitted by amateur astronomers around the world will show slight differences in the asteroid’s position due to parallax. Along with each observer’s location, this parallax information will be used to find a precise distance to Eros, just like professional astronomers did in January 1931.

Among the telescopes aimed at Eros are the robotic 1.2 meter MONET telescope at the McDonald Observatory in Texas and its twin at the South African Astronomical Observatory in South Africa. The two telescopes are employed for education purposes and remotely controlled by students. Another educational telescope, the 2 meter Liverpool Telescope on the Spanish island of La Palma, will probably also be used to get images of Eros.

The Eros Parallax Project is first and foremost just fun to participate. You don’t have to be an experienced astrophotographer to be able to make valuable observations. An ordinary SRL camera with telephoto lens, mounted on a tripod, may already give satisfactory results. Using free, online software you will determine the celestial coordinates of Eros on your images and submit the data to our website. Using the data submitted by you and all other participants, the distance to Eros will be calculated. The instructions on our website are clear and simple to follow.

But the Eros Parallax Project is also a great educational opportunity – the data and submitted images will be made available for classrooms to use to process the submitted figures themselves. This resource will last forever, and will certainly inspire some young astronomers to take part the next time Eros comes close to Earth again. It will also prepare classrooms for the even rarer event coming in June – the transit of Venus. Along with enjoying the night sky, developing observing skills and gaining an understanding of our solar system, participants and the students who benefit will repeat the work of the professional astronomers of the 1930s and learn about real research.

The Eros Parallax Project is run under the aegis of Astronomers Without Borders and is open to everyone. So, join this international campaign, get out with your camera or telescope and start shooting Eros tonight! Don’t forget to submit your measurements and to upload your pictures to our online depository.

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1874 transit from Down Under (2)

Posted on January 26, 2012 by Nick Lomb

In the previous post I considered the preparations of Henry Chamberlain Russell, the director of Sydney Observatory, for the 1874 transit and the magnificent illustrated book that he published on the event. Here I show a couple of the illustrations from the book.

HC Russell’s observations at the end of the transit as seen from Sydney Observatory. Photo lithograph from Observations of the Transit of Venus, 9 December, 1874. Powerhouse Museum Research Library

Russell observed with the new 29-cm or 11½-inch refractor or lens telescope from Hugo Schroeder of Hamburg, Germany. To reduce the heat from the Sun he used an aperture to reduce the main lens to 5 inches (12.5 cm) in width and coloured glass filters in front of and behind the eyepiece. From Sydney the transit began just before local noon and within a few minutes he could see the aureole on the part of the planet still outside the disc of the Sun. He described what he could see as, ‘It was very remarkable and beautiful, like a fringe of green light, through which the faintest tinge of red could be seen’. Since Russell was looking through coloured filters the colours that he describes may not be real.

Four hours later Venus was again at the edge of the Sun prior to egress. In his illustration of the egress Russell presents a sequence of five images with time increasing to the left. Though Russell emphasises that he did not see ‘the black drop’ in the first drawing of the sequence, made just after internal contact, we can see some haziness that is clearly due to similar or the same atmospheric effects as the black drop. Two minutes later the aureole that he called the ‘halo’ was clearly visible on the part of Venus off the Sun. Another 15 minutes later he says, ‘the halo was for the first time seen irregular–in diameter it seemed considerably broader at the north pole of the planet as shown’. For the last few minutes before the planet completely left the Sun, Russell was struggling with poor definition due to approaching clouds, but a white patch could be seen near the north pole of the planet.

Amateur astronomer Mr Alfred Fairfax’s drawing of the aureole through a 4¾-inch (12-cm) lens telescope. The scale of the aureole is greatly exaggerated to allow details to be shown. Photo lithograph from Observations of the Transit of Venus, 9 December, 1874. Powerhouse Museum Research Library

The aureole is due to sunlight refracted through the atmosphere of Venus, but why was there a brightening near the pole of the planet? This went unexplained for 130 years until the 2004 transit. In an article in the Astronomical Journal (141:112 (9pp), 2011 April) Jay M. Pasachoff, Glenn Schneider, and Thomas Widemann indicate that they saw the same effect with the TRACE spacecraft, this time with a brightening near Venus’ south pole. They explain their observations and those of Russell by appealing to previous spacecraft observations of the structure of the planet’s atmosphere. The observations indicate a ring or torus of cold air surrounding each of the poles of the planet that lower the average cloud top height by about 10 km. Extra sunlight can thus stream through regions surrounding the poles of the planet to create the polar spots.

Russell would have been thrilled to have his observations explained. Maybe the 2012 transit will lead to an explanation of those by Mr Fairfax!

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What did Horrocks really see?

Posted on January 25, 2012 by Steven van Roode

Most of us don’t know, but we have been deceived for hundreds of years with regard to Jeremiah Horrocks’ observation of the 1639 transit of Venus. Every picture showing the Cytherean silhoutte on the solar disk as recorded by Horrocks turns out to be plainly wrong. The source of all error: seventeenth century astronomer Johannes Hevelius.

Horrocks didn’t leave us any drawings of what he saw on that fateful day of December 4, 1639. All we have to go by is the wordy account of his observation, of which it is a miracle that it has come down to us at all. After his early death, several unfinished autograph manuscripts of his account Venus in sole visa were found in 1659 by John Worthington, Master of Jesus College, Cambridge, among the papers of the young astronomer’s friend and co-witness of the transit William Crabtree. Worthington sent two of the latest drafts to Samuel Hartlib, who in turn sent them to the mathematician Nicolaus Mercator, so that these could be combined into a single document – a publication that never came to be. The Greenwich Observatory and the Cambridge University Library currently hold three handwritten copies, which could be identified as identical to one of the copies sent to Mercator. A poor transcription and conflation based on these two manuscripts was obtained by Christiaan Huygens from Paul Neile, who sent it to Johannes Hevelius. The latter would finally publish Horrocks’ Venus in sole visa as an annex to his book Mercurius in sole visus Gedani, published in 1662.

Hevelius added an image of the solar disk to the report, based on Horrocks’ description of his observation. This is the first image that’s in error.

Hevelius’ image (to the left) shows the solar disk, with the zenith at the top and the three positions of Venus as observed by Horrocks’ between ingress and sunset. However, if the path of Venus relative to the zenith is computed for the 1639 transit as observed from Much Hoole, the difference with Hevelius’ rendering becomes readily apparent: in the image of Hevelius, Venus is moving towards the horizon, whereas in reality Horrocks must have seen the planet moving towards the zenith. Also, the three positions of Venus are spaced equally in Hevelius’ drawing, whereas the three observations by Horrocks were made at intervals of 20 and 10 minutes respectively.

This representation of the solar disk is not how Horrocks would have seen the image of sun on his screen. The solar image projected by the Galileian telescope used by him, was inverted top to bottom, but not left to right. So, while Venus was in the bottom-left corner of the sun in reality, Horrocks would have seen Venus in the top-left corner of the projected image. Hevelius however, in his printed publication of Horrocks’ account, changes the astronomer’s own words to place Venus in the top-right corner of the projected solar image:

Primò pro Inclinatione Lineâ diametrali perpendiculariter ad Horizontem insistenti circuli tamen plano ob Solis altitudinem aliquantum reclinato, inveni Veneris umbram hora dicta 3 15’ Solis discum intrasse grad. 62 30′ circiter (certe inter gr. 60 & 65) à vertice ad dextram.

(In the first place, with respect to the inclination, the line of the diameter of the circle being perpendicular to the horizon, although its plane was somewhat inclined on account of the Sun’s altitude, I found that the shadow of Venus at the aforesaid hour, namely fifteen minutes past three, had entered the Sun’s disc about 62 30′, certainly between 60 and 65, from the top towards the right.)

The three handwritten manuscripts of Venus in sole visa all have “ad sinistram” (to the left) instead of “ad dextram”, as does a mid-1659 letter of Nicolaus Mercator to Samuel Hartlib, quoting directly from Horrocks’ own writing. Still, Hevelius thought Horrocks was in error and changed it to “ad dextram”. Also, John Wallis added the note “lege dextram” (read right) after “sinistram” in his Opera Posthumus of Horrocks. Both Hevelius and Wallis must have been confused about the orientation of the projected image by a Galileian telescope. Their error is also reflected in three historic paintings of the 1639 observation of the transit of Venus.

The 1903 painting of Jeremiah Horrocks by J.W. Lavender (to the left) and the mural by Ford Madox Brown from the 1880s showing William Crabtree (in the middle) both have the silhouette of Venus at the top-right corner of the solar disk, while is should have been in the top-left corner. The third painting, a 1891 oil painting by Eyre Crowe (to the right), doesn’t show Venus at all, but the eyes of Horrocks are directed to the upper right corner of the solar image. The 1859 stained glass window in the church of Much Hoole also shows Horrocks viewing the projected image of the sun; here, Venus is incorrectly at the bottom-left corner.

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The aureole as an artefact

Posted on January 23, 2012 by Steven van Roode

This is a little late, but I still want to draw some attention to a good article about the transit of Venus in the German magazine for practical astronomy Interstellarum. In its August/September issue it ran an in-depth article by Susanne and Peter Friedrich. One of the surprising things to me was that the authors, in discussing the various phenomena that may be observed during ingress or egress, distinguished between the Lomonosov Ring and the aureole effect:

Der Lichtring, nach seinem Entdecker auch Lomonossow-Ring genannt, war beim Venustransit 2004 während des Ein- und Austritts im Fernrohr eindeutig zu erkennen. Er entsteht durch Brechung von Lichtstrahlen in der dichten Venusatmosphäre. Aufgrund der unterschiedlich starken Brechung in verschiedenen Höhen der Venusatmosphäre und entlang des Lichtweges tragen Lichtstrahlen von verschiedenen Regionen der Sonnen zum Lichtring bei.
   Nicht mit dem Lomonossow-Ring verwechseln sollte man helle Säume um das Venusscheibchen, sog. Aureolen, die auf manchen Fotos nach exzessiver Bildbearbeitung auftreten können. Im Gegensatz zum Lomonossow-Ring treten diese Aureolen nur auf, wenn sich die Venus vollständig vor der Sonnenscheibe befindet.

So, what we commonly call the aureole effect, is here named after Lomonosov (who may not have seen the aureole at all in 1761, as his actual wording seems to correspond better to a black drop than to an atmosphere of Venus), while a luminous ring around the disk of Venus when it’s still on the Sun is designated the aureole. Though the entire article is well-written and provides sound information, I have to disagree on this particular point.

Below are two pictures, taken during the 2004 transit of Venus, showing the two effects described by the Friedrichs. The picture on the left, a stack of 88 video frames by Ralph Vandebergh, shows Venus against the sun’s photosphere. Here, a bright ring around Venus’ silhouette is visible. The second image, also by Ralph Vandebergh, shows the aureole off the solar disk.

This last image shows the genuine aureole effect. It’s the sun’s light refracted by the Cytherean atmosphere, making the planet’s atmosphere shine as a faint arc of light. But the surface brightness of the arc is still much fainter than the sun’s photosphere, causing the effect to be invisible when the disk of Venus is seen entirely on the solar disk. The luminous ring around Venus in the first image therefore can’t be the planet’s atmosphere.

What could it be? The Friedrichs hint at its origin in their description: the effect is seen only after excessive image processing. Most likely this is a digital artefact, created along abrupt brightness transitions when the image’s sharpness and contrast are improved. This 2004 image of Venus by a solar telescope at Pic du Midi for example does not show the luminous ring at all. Yet, some might notice that even in this image Venus still seems to be surrounded by an indistinct thin region. This most likely is a common Mach band, the light zone seen at the onset of luminance gradients that lack any photometric basis. The next transit of Venus may give us a decisive answer about this.

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Out of Diaries: 22 January 1761

Posted on January 22, 2012 by Andrea Wulf
The interior of a Russian cottage according to Chappe – complete with a half-naked woman (Wellcome Trust, London)

The interior of a Russian cottage according to Chappe – complete with a half-naked woman (Wellcome Trust, London)

On 22 January 1761, the French astronomer Chappe d’Auteroche arrived in Warsaw. He was on his way to Tobolsk in Russia – a dangerous journey across war-torn Europe. The weather had been dreadful – when incessant rain had turned the roads into mud, he had then swapped his carriage for a boat but thick fog allowed them only to travel during the day. All the while the celestial clock was ticking.

The journey had been beset with problems. In Vienna he had bought a new carriage and on 10 January, the fateful day that Mason and Dixon’s ship was attacked by the French and Pingré zigzagged across the ocean to escape the British, Chappe’s carriage (including half a ton of instruments) had crashed into an icy ditch somewhere between Brno and Nový Jičín, in today’s Czech Republic. It had taken hours of pulling and shoving to free the battered vehicle. Chappe had enough. It had been the first time that the usually optimistic Chappe allowed himself to contemplate defeat. ‘I began to fear’, he wrote in his diary, that ‘we should not reach Tobolsky in due time’. Tobolsk was one of the most important locations because the entire transit would be visible and would be at its shortest – making Siberia the perfect counterpart to the longer transits in the East Indies (for example Bengkulu where Mason and Dixon had been dispatched to).

While his colleague Le Gentil was suffering the humid heat in Mauritius, Chappe endured a cold he ‘had not before experienced’. Even inside the carriage the temperatures were so low that he fumbled out his thermometer with numb fingers and scrawled in his journal ‘eleven degrees below 0’. The jovial Chappe was delighted when they finally arrived in Warsaw where he was welcomed in style. It was the season of the carnival – a ‘season devoted to pleasure’, as Chappe noted – and the French astronomer attended a great many festivities with the Polish aristocracy. The French ambassador even introduce Chappe to the King of Poland.

Chappe’s diary entries from Warsaw show that he was not only an astronomer but also a connoisseur of women – describing in detail their dress and ‘undress’. No matter how difficult his voyages, he always found time to investigate women with the taxonomic precision of a scientist. No matter how cold or exhausted he was, he remained an expert of the female sex and remarked appreciatively on their sparking eyes, the ‘slenderness of their waists’, and ‘well-shaped servant maids’. The women in Warsaw, he declared, were beautiful and sociable but also ‘strictly virtuous’.

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A pamphlet from the Pacific

Posted on January 21, 2012 by Steven van Roode

The Astronomical Society of the Pacific has put together an eight-page PDF booklet The 2012 Transit of Venus, based on the article by Paul Deans in the spring 2011 issue of Mercury. Deans explains the science of transits, describes the attempts to make critical measurements of Venus transits during the 18th and 19th centuries, and discusses where and when to view the upcoming 2012 transit. It also includes a list of resources and a section on how to safely view the transit.

This small booklet provides a wonderful way to introduce your students to the transit of Venus. All the elements that make up the story of the transit are there, and it directs to many other online sources to gain more in-depth knowledge. But the best thing is that Deans persuades his readers to go out on June 5 or 6 and see the transit with their own eyes:

June 5/6, 2012, is your opportunity to see it. So, where will you be during next year’s transit of Venus?

So, where will you be?

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Set sail on HMB Endeavour

Posted on January 20, 2012 by Chuck Bueter

Replica Endeavour

What would it be like to sail on the HMB Endeavour akin to James Cook, then witness the transit of Venus from a Pacific island? Stop dreaming and start doing. The Australian National Maritime Museum, which is the steward of the replica sailing vessel commanded by Cook in 1769, is holding a ballot to select the 35 persons who will pay to crew the HMB Endeavour for a 13-day adventure. The trip is scheduled to depart Sydney Harbor on May 31, sail about 600 km to Lord Howe Island in time for the June 6 (AEST) transit of Venus, then return by June 12.

This is no frilly 13-day cruise, either. Voyage crew, at $4,000.00 AUD per berth, “sleep in hammocks and stand watch, handle the rigging, furl the sails, clean and steer the ship. Voyage crew must be able to climb aloft (39 metres in a harness).” For those thinking more along the lines of the captain’s accommodations, the next closest option is the Supernumeraries category for $8,000.00 AUD, for which you get your own cabin and have a choice in participating in the shipboard rigors, though encouraged to do so.

Onboard will be Sydney Observatory Astronomer Carlos Bacigalupo and the Endeavour’s regular crew. The destination, Lord Howe Island, is on the World Heritage list. Of course, the main attraction is the 2012 transit of Venus. The online balloting for slots is open now through February 10, 2012.

Get off your chair and into a real hammock. The adventure of a lifetime may await, as you follow in the wake of James Cook and his gutsy crew. By the end of the trip you’ll have a great appreciation for 18th century life aboard HMB Endeavour, and you’ll know the difference between HMB and HMS.

Details at http://www.endeavourvoyages.com.au/.

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A round bird, or…

Posted on January 19, 2012 by Steven van Roode

A cartoon by Bill Kramer. Did the Ancients notice a transit of Venus and write it off as something else? What would your best guess be?

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The 1874 transit from Down Under

Posted on January 18, 2012 by Nick Lomb

The main Australian observing stations for 1874 transit of Venus. Sketch Nick Lomb

Like the June 2012 transit of Venus, the December 1874 transit was visible in its entirety from Australia. The observatories at Sydney, Melbourne and Adelaide, which are the capitals of the three main states or colonies at the time, made plans to ensure that the rare event was well observed. In addition, there were two United States observing teams in the island state of Tasmania.

In subsequent posts I will discuss the plans and activities at the different places. Here I would like to introduce you to the magnificent book published by Henry Chamberlain Russell, the director of Sydney Observatory, about the 1874 transit observations in 1892. Images from this book are used in almost every book or article published in recent times on the transit. Disappointingly, the images are often not credited or wrongly credited to Charles Potter, the Government Printer, whose name is prominent on the front cover of the book.

In preparation for the transit Russell obtained new instruments including a 29-cm or 11½ -inch refractor or lens telescope from Hugo Schroeder of Hamburg, Germany that is still one of the treasures of Sydney Observatory. He also arranged for three observing stations at country sites to maximise the possibility of obtaining observations if the weather was poor. To staff these extra stations he recruited best scientific men in the Colony including Archibald Liversidge, the newly appointed professor of geology at the local university.

The cover of Henry Chamberlain Russell’s book on the 1874 transit of Venus. Courtesy Powerhouse Museum Library

Immediately after the transit Russell requested all the observers to submit written reports as well as illustrations of their observations. He intended to publish these results as soon as practicable, writing to the Under Secretary of Finance and Trade on 30 January 1875:

“The results obtained in New South Wales during the recent Transit of Venus are of the greatest importance, both in a scientific point of view, and also with regard to the credit due to this Colony for the position taken in this important scientific matter.

In order to make the results generally known they must be printed in a first class style, reproducing in the book all drawings photographs &c so far as possible. If this is properly done the work will become known all over the scientific world, and great credit will accrue to this Colony.”

Russell goes on to explain that his absence overseas (to report in person to the Astronomer Royal at Greenwich) would not cause undue delay as, in any case, the lithographs would take six months to produce. In the event it took 18 years for the book to be published. Why the long delay? I think that it was the fault of the Government Printer and the manuscript had languished with the printer for most of the 18 years. When I found the originals of the book and its illustrations in the Observatory archives there was a note with them from Russell saying to the printer that the book has been delayed for long enough and to please get on with publishing it.

In the next post we will look at a few of the illustrations from the book and discuss why recently they have been found to provide useful information about the atmosphere of Venus. We will also consider the controversy surrounding a significant omission from the book.

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Out of Diaries: 17 January 1761

Posted on January 17, 2012 by Andrea Wulf

Today, 251 years ago, on 17 January 1761, Nevil Maskelyne and his assistant sailed to St Helena to view the transit there – one of the few observation locations in the Southern hemisphere and therefore an important counterpart to those in the far north. St Helena was a lone speck of land in the South Atlantic and had been in the possession of the British East India Company for nearly a century. It was an important stopover on their trading route and Maskelyne was hitching a ride on an East Indiaman.

The twenty-seven-year-old Maskelyne was a curate in Chipping Barnet, a small town to the north-west of London, but he seemed to have preferred astronomy to the Bible. Maskelyne had been a fellow of the Royal Society for a few years and had volunteered to sail to St Helena. Not only had he made sure to have the best instruments but he also managed to receive a very generous liquor allowance – the bill for wine and spirits accounted for almost one-quarter of the entire budget for the expedition.

Maskelyne’s ship was accompanied by several heavily armed vessels which were sailing to the West Indies.  At the Canary Islands the convoy turned west while Maskelyne’s ship continued south. During those long weeks on board he tested his lunar method of determining longitude at sea. Night after night, Maskelyne peered through his telescope, measuring the moon’s path across a tapestry of fixed stars. Page upon page, he scribbled his observations and calculations in his note book. ‘My principal attention on board’, Maskelyne later told the Royal Society, was ‘to be satisfied … of the practicability of that method’. There was only one problem with his lunar method: it involved such complicated calculations that sailors couldn’t glance quickly into the sky to work out their longitude. Each of the calculations was so complex that the whole process took around four hours, which was no problem for Maskelyne who adored lists and order.

But it was not all hard work on board ship. Traveling with more than one hundred gallons of wine and rum as well as five gallons of spirits and over seventy bottles of claret, Maskelyne noted that it was ‘a very agreeable voyage’.

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