Continue reading »]]> And so after 10 days, I finally had a chance to play with my new telescope on Friday night! Optical astronomy requires at least a few gaps in the clouds but last night at 8pm it was completely clear – I was hopping up and down like an overactive child waiting for the sun to go down (scheduled for about 8:40pm) and simultaneously cursing the slightest wisp of cloud. It should be clear that I’m a bit new to this, so what I write shouldn’t be seen as in the slightest bit authorative.

Kindly folk at @newburyastro had suggested Venus and Saturn as targets for my first adventure into the night. Useful advice because, as a relative beginner I had little idea what I was going to see, or in fact when I was going to see it. Venus become visible at about 9:20pm towards the now-set sun, it turns out that pointing the ‘scope with the finderscope is much easier than the rather more hazardous enterprise of finding the sun without (something I describe here). In the eyepiece Venus appears as a small, bright crescent.

It was a breezy evening which meant that my view jiggled about a bit, it also jiggled about a bit whenever I touched the telescope. However I did manage a picture of Venus taken on my Canon 400D at prime focus. This is an uncropped view, and it’s upside down.

Venus (1/50 second, ISO200)

Mars made an appearance a little later at about 9:35pm along with a bright star which I believe is Regulus. This enabled me to get my telescope to work out how it was orientated meaning it could track to objects on demand and also tell me what I was looking at (very handy for a novice). My picture of Mars is a little uninspiring, I’ve zoomed in here as far as possible, in Mars’ favour it does look red and it isn’t a simple point.

Mars (cropped, 1/3 second, ISO200)

By now more and more stars were coming out, so I thought I’d try out my piggyback mount. This image is taken with a 10mm lens (i.e. really wide angle) with the telescope simply used as a camera mount pointed at Polaris, it’s a 30s exposure.

The Northern circumpolar region (Canon 400D, 10mm, 30s ISO200, f/4)

It took a while to get this because I had auto-focus on and the camera couldn’t find anything to focus on so wouldn’t fire – switching off auto-focus and focusing to infinity manually resolved this. It was at this point I wished I could remember how to switch the display on the back of my camera off because it was really bright, and remember which button was which without being able to see it. The thing that surprised me about this is that there are rather more stars than I could see with my naked eye and some of them are quite strongly coloured. I feel I should go about identifying the stars in my picture.

At this point I thought I’d give Saturn a go, I must admit I thought it was hidden behind buildings and trees from my position in the back garden but I punched it into the telescope handset and it pointed me into the side of the conservatory, so I picked up the telescope and moved it one metre to the right, peered through the finderscope and tweaked my direction a bit and… the planet with ears popped into view!! This was really exciting! I only have one eyepiece for my telescope and it’s quite low magnification but through the eyepiece I could see my target was not a point, and it was not round – it was shaped like a flying saucer and there were slight gaps either side of the central body. Having marvelled at this for a bit I thought I’d try for another photograph:

Saturn (cropped, 1/4s, ISO200)

It’s not the best picture of Saturn taken last night but it is my picture!

The moon hadn’t risen before I went to bed, so when I spotted this morning I rushed out for a photo.

The Moon 9(1/500s, ISO400)

I’ve not done any astrophotography before these (apart from my shots of the sun, and a couple of shots at the moon through a conventional lens). I guess the thing I carried over from that was that the moon is a rock in full sun, so you need to set your exposure times accordingly, the same is true for Mars and Venus so I suspect I should be using shorter exposure times for them to which will also reduce any motion blur.

My first night of viewing has highlighted a need to have a better grip of how to work your camera, plan what you want to look at in advance and, as with an SLR camera, a telescope is simply a gateway drug for further accessory purchase.

Continue reading »]]> This post is a review and summary of Larrie D. Ferreiro’s book “Measure of the Earth” which describes the French Geodesic Mission to South America to measure the length of a degree of latitude at the equator. The action takes place in the 2nd quarter of the 18th century, the Mission left France in 1735 with the first of its members returning to Europe in 1744.

The book fits together with The Measure of All Things by Ken Alder, which is about the later French effort to measure a meridian through Paris at the turn of the Revolution in order to define the metre, The Great Arc by John Keay on the survey of India and Map of a Nation by Rachel Hewitt on the triangulation survey of the United Kingdom.

The significance of the measurement was that earlier triangulation surveys of France had indicated that the earth was not spherical, as had pendulum measurements made by Jean Richer in Guyana in 1671 which showed a pendulum there ran 2:28 slower there than in Paris. A Newtonian faction believed that the earth was flattened at the poles, its rotation having led to a bulging at the equator. A Cartesian school held that the earth was flattened around the equator and bulged at the poles, this was not a direct result of work by Rene Descartes but seems to have been more a result of scientific nationalism. Spoiler: the earth is flattened at the poles.

From a practical point of view a non-spherical earth has implications for navigation – ultimately it was found that polar flattening would lead to a navigational error of approximately 20 miles in a trans-Atlantic crossing although at the time of the Mission it was believed it could have been as much as 300 miles. Politically the Mission provided an opportunity for the French to form an alliance with the Spanish, and to get a close look at the Spanish colonies in South America which had provided huge wealth to Spain over the preceding 200 years. Ferreiro provides a nice overview of the L’Académie des Sciences under whose aegis the mission was conducted,and of the Comte de Maurepas, French minister of the navy and sponsor of the Mission.

The core members of the Geodesic Mission were Pierre Bouguer, Charles-Marie de La Condamine, and Louis Godin they were accompanied by Spanish Naval cadets Antonio de Ulloa y de la Torre-Guiral  and Jorge Juan y Santacilia. Other members were Joseph de Jussieu (doctor and botanist), Jean-Joseph Verguin (engineer and cartographer), Jean-Louis de Morainville (draftsman and artist), Theodore Hugo (instrument maker), Jean-Baptiste Godin des Odonais and Jacques Couplet-Viguier.

Louis Godin, an astronomer, was the senior academician and nominal leader of the mission. Pierre Bouguer, was a mathematician, astronomer and latterly geophysicist: as well as the measurement of the degree of latitude he also attempted to measure the deflection of a plumb-line by the mass of a mountain – an experiment which Nevile Maskelyne was to conclude successfully in 1775, I wrote about this here. Bouguer also wrote a treatise on ship building whilst away in South America. Charles-Marie de La Condamine could best be described as an adventurer although he was also a competent mathematician and geographer, it was his more lively writing on life in South America which would have a bigger impact on their return to Europe.

The scheme for the determination of the length of a degree is to measure the length of a meridian (a line of longitude) close to the equator by triangulation, making a ground measurement baseline to convert the angular measurements of the triangulation survey into distances and a second baseline to confirm your workings; the latitudes of the ends of the triangulation survey are determined astronomically by measuring the positions of stars. I’ve read of this process before, the new thing I learnt was the method for aligning up your zenith sector with the meridian – which I’m tempted to try at home.

These measurements were done in the area around Quito, in modern Ecuador (named after the equator), the endpoints of the survey were at Quito in the north, close to the equator and Cuenca approximately 200 miles south. During the survey, through the Andes, the team scaled peaks as high as Mont Blanc (and suffered altitude sickness for their troubles) which would not be climbed for another 50 years. The survey was repeated in the early years of the 20th century and even then it took 7 years – the same length of time as the original survey, due to the transport difficulties presented by the terrain.

The work of measuring the meridian was made more difficult by the journey to get there (which took the best part of a year), the terrain and conditions when they got there (mountainous and cloudy), the poor leadership of Godin, local political machinations and the mother country cutting them loose financially. Ferreiro makes a lot of Godin’s poor leadership, some of which is justified – he spent Mission money on prostitutes and regarded the Mission funds as his own purse. Frequently the Mission split into two groups, one containing Bouguer and La Condamine and the other Godin – sometimes this is quite appropriate, in duplicating measurements for consistency whilst on other occasions it is simply fractiousness.

To a degree the Mission was scooped by measurements made above the Arctic Circle in Lapland, this mission was also promoted by the L’Académie des Sciences, led by Pierre Maupertuis (a rival of Bouguer) and Anders Celsius. It completed its work in 6 months, well before the Geodesic Mission had finished their work, discovering that the poles of the earth were flattened. However, doubts remained over the results and the full determination required the data from the equator. Bouguer presented this on his return to France, to great acclaim, showing that the earth was flattened by 1 part in 179 (later measurements showed that the flattening is actually smaller at 1 part in 298).

The Mission spawned a wide range of publications by its members, covering not only the geodesic component of the work but also regarding life and nature in South America. Ferreiro credits La Condamine’s work in particular has setting the context of how South America was viewed for quite some time after the mission. The Spanish officers also made in impact an highlighting colonial misrule back to their home country. Arguably the international collaborative elements of the Mission set the scene for the measurements of the transit of Venus later in the 18th century.

Ferreiro makes a comparison between the French Geodesic Mission, which was centrally run by the state and the British Longitude Prize, which although state funded was privately executed, implying that the former was superior. It’s not clear to me whether he’s engaging in a degree of hyperbole here, since the Mission was to some degree an organisational car-crash and was in large part funded from La Condamine’s own purse at the time. Furthermore, L’Académie des Sciences also awarded prizes – having copied the British government in this and the Royal Society was from the outset a very internationally oriented organisation. So the picture as Ferreiro presents it is something of an over-simplification.

I found the book very readable, its clearly based on a large quantity of primary source material and covers a great deal beyond the simple mechanics of the Geodesic measurements.

Footnotes

My Evernotes on the book are here.

Continue reading »]]> I’ve had my new telescope (a Celestron NexStar 5SE) nearly a week now and so far I have images of miscellaneous chimney pots, arials, pigeons, and… the sun. Only the last of these can be considered fair astronomical game, I’ve had two goes at it so far. I tending to the view that my telescope blog posts shall be like a lab book of what I have done rather than a guide to others, except to perhaps highlight those things that are obvious to experienced astronomers but not to the novice.

The first rule about looking at the sun through a telescope is:

Do it carefully with the appropriate solar filter in place

Seriously, be really careful pointing telescopes at the sun – mine is a small one and it concentrates light by a factor of 300, looking near the sun with the naked eye is bad – imagine x300 more light!

I bought a sheet of Baader AstroSolar solar filter film at the same time as I got my telescope, this comes in the form of a thin A4 sheet of material that looks like foil. It has an optical density of 5, meaning it lets 0.001% of the incident light through. There are detailed instructions supplied with the AstroSolar film for constructing your own mount for the material, or you could go and buy a proper mounted filter (here).

The aim of the filter mount is to hold the filter film without stressing it and in a manner convenient to attach it to the front of your telescope. I should, perhaps, have used the “thick card” that the instructions recommended rather than the corrugated cardboard from the box the telescope came in, and it turns out double-sided carpet tape is really exceedingly sticky. However, the result shown in the image below is functional and I have included a built-in “filter shield” of my own invention for storage. Behind the two cardboard rings sandwiching the filter is a cardboard tube which fits neatly over the optical tube.

Celestron NexStar 5SE with homemade solar filter from Baader AstroSolar

The next challenge is pointing the telescope at the sun, this turns out to be pretty tricky because with a solar filter in place the only thing in the sky that you can see is the sun, the field of view on my telescope is approximately the size of the moon, you can’t navigate by distinctive clouds and you can’t look through your finderscope unless it is also solar filtered. I’d read that you should move the telescope until the shadow of its tube is a circle – I tried doing this on the ground (minimising the area rather than trying to get a circle). At one point I thought I’d found the sun but from later observations I suspect I was staring at an internal reflection. But easier, since my telescope has a non-magnifying StarPointer finderscope I cast the shadow of that onto a piece of card until it looked round (see image below). The second time I tried this, I got a “hole-in-one” – the sun in my field of view at the first attempt! I could improve this by slotting a disk with a small hole in the middle into the finderscope and aligning until a bright spot appeared in the middle.

Shadow of the Celestron Star Pointer, used to align the telescope to the sun

 I have to say that seeing the sun through my telescope for the first time was as exciting as digging up potatoes, that’s to say really exciting!

I then moved to trying to photograph my target, I did this using a Canon 400D SLR. The camera is attached by a T-mount to the back of the telescope, in place of the eyepiece. This means that the telescope is replacing the camera lens,s known as “prime focus photography”. Two configurations are possible: with and without the “Star Diagonal” in place. The field of view through the Star Diagonal is smaller, and dimmer than the direct connection however the viewing position is more comfortable and there is less risk of the camera falling off! The direct connection gives a correctly oriented view through the camera, whilst the Star Diagonal gives an upside-down view. The focus position for the eyepiece and the two different camera configurations are all different. The camera is triggered using a remote release cable.

My first attempt is shown below, this is a 1/640s at ISO200 taken without the StarDiagonal:

Image of the sun, Canon 400D ISO200, 1/640s exposure

Below are crops to the two visible clusters of sunspots:

Sunspot detail

Sunspot detail

These look a little less distinct than they did through the eyepiece which may have been because I forgot to enable “mirror lockup”. The second time around I did a bit better, this is taken at ISO100 with a 1/125s exposure again without the StarDiagonal:

Image of the sun, Canon 400D ISO100, 1/125s exposure

With a detail of the sunspots:

Sunspot detail

I have a nice set of solar features, sunspots with dark umbra and a paler penumbra, limb darkening (the sun appears less bright towards its edges) and plages (related to faculae) which are bright spots, these are pretty difficult to see. The image below is a crop of the sunspot area to the right hand side of the image above with some contrast enhancement (I boosted the shadows using Picasa) which just about shows the plages:

Solar photo showing plages

Next time I should probably set the white balance to something other than “auto”, and experiment a bit with exposure times to see if I can get the plages showing up a little better. A Barlow lens would give me some magnification of the sunspots… and so the spending on accessories begins!

Continue reading »]]> This is a brief overview of my shiny new purchase: a Celestron NexStar 5SE telescope. As an experiment I have also embedded a video review (here), I should also point out that so far cloud cover has meant the only celestial object I have observed is the sun (using the appropriate safety measures).

I bought my ‘scope from Sherwood’s, who I am happy to recommend for their good prices, and quick and efficient service. My purchase list was as follows:

• Celestron NexStar 5SE (with mains adaptor)
• SLA AstroPower station 12v 7Ah battery pack
• Piggyback mount for my Canon 400D SLR
• Universal camera adaptor and T-mount for similar
• Moon filter
• Baader solar filter film

The mount is powered, the add-on battery pack seemed like the best option for providing that power conveniently. I have a Canon 400D SLR camera which I wanted to use with the telescope, the piggyback mount lets me put the camera on top of the optical tube and simply use it to point the camera at the sky. The T-mount assembly allows me to use the telescope as a camera lens, albeit without auto-focus and aperture.

The solar filter is essential if you want to look at the sun, and I got the impression a moon filter was useful for dimming the brightness of the moon, photographers will know that when photographing the moon the exposure time is as if for a rock sitting in full sun, which is exactly what it is!

The 5SE is a Schmidt-Cassegrain telescope with a 125mm (5 inch) primary mirror, a focal length of 1250mm and an overall F/ratio of 10. “Schmidt-Cassegrain” means that the open end of the tube has a corrector plate (Schmidt’s contribution) and light is focussed by a large concave primary mirror and a smaller convex secondary mirror in the centre of the corrector plate. The image is viewed through an eyepiece in the back of the optical tube, behind the primary mirror. In practical terms it also means the telescope has a very short tube length making it more portable than similarly specified telescopes. The whole assembly is easy to pick up and carry in its deployed state, and the optical tube in particular was well-packed on delivery forming the basis of a useful carrycase.

The telescope is supplied with a 25mm focal length eyepiece which gives a magnification of x50, the maximum useful magnification of the telescope should be x300 with appropriate eyepiece. Focus is achieved by turning a knob on the back plane of the telescope tube, which moves the primary mirror. The eyepiece is attached to a periscope (Star Diagonal in Celestron’s parlance) to give a more comfortable viewing position. The finderscope is a Celestron Star Pointer, which is a non-magnifying window with an LED spot projected to the middle for guiding, it took me a little while to get the hang of this but I can see the benefit of a low magnification finderscope.

The telescope is on a computerized alt-azimuth mount which also includes an equatorial wedge (like the equatorial platform), meaning that the rotational motion of the mount can be made co-axial with that of the earth – allowing un-rotated tracking of objects through the sky for astrophotographic purposes. The controller is a handset device on a cord, in night time operation the telescope can be aligned to the night sky by pointing it to three different stars, after which it will goto any one of a huge catalogue of celestial objects selected using the handset.

The optical tube feels nice and chunky, although the finderscope is a bit plasticky. The piggyback mount attaches using the same mounting holes as the finderscope, the finderscope then bolts back on top, I did a bit of tweaky of the screws along with adjustments on the finderscope to get it aligned. I have achieved fine views of my neighbours chimney pot!

There is a battery compartment in the mount which takes 8xAA batteries, reading on the internet I understand the lifetime for this set is about 30 minutes in operation, which is why I got both a mains adaptor and a 3rd party battery pack. I suspect I’ll mainly use the add-on battery pack for the convenience of fewer trailing leads. The mount doesn’t operate without power, which is a bit of a drawback, the telescope can be tilted but not rotated. The mount sits on top of a nice chunky tripod, to which it is attached by three screws, so in principle you could make yourself a “manualised” version by sitting the scope on a turntable. I have the slightly spurious desire to see a graduated scale on the mount movements. I’m used to using research grade optical equipment and whilst the optics have that feel about them the mount, although functional, does not.

The telescope comes with TheSkyX (First Light edition) planetarium software, and also an application called “NexRemote” which seems to allow you to control the telescope using a virtual version of the handset on screen – this seems a bit pointless to me! Other telescope control software is available, and it appears there is an interface standard. The programmer in me is hankering to write my own controller software!

Overall I’m pleased with my new purchase but desperate for a slightly less cloudy night to try it out properly – no doubt more blog posts to follow once I’ve done this! Even at £650 for the telescope it is cheaper than many lenses for my Canon SLR, although it is a little chastening that John Hadley’s 1721 reflecting telescope had a larger primary mirror.

Here is a video tour, which covers much of what I’ve written above but includes the sound of me tripping over the cat’s water bowl:

Continue reading »]]> The BBC published an article entitled “Viewpoint: Is UK GDP data fit for purpose?” which featured a graph showing the original estimates for quarterly UK GDP growth and current estimates for those same figures. The point being that the original figures are subject to revision which can change figures quite significantly, for example currently we are technically in recession with a GDP growth figure for Q1 2012 of –0.2% (source). But how does this compare with the size of the revisions made to the data?

Here is the graph from the original article:

This is quite nice but there are other ways to display this data, which unfortunately isn’t linked directly to the graph. However, this should not stop an enterprising number-cruncher, there exists software which will allow you to extract the numbers from graphs! I used Engauge Digitizer, which worked fine for me – I had the data I wanted 20 minutes or so after I’d downloaded the software. It does some semi-automatic extraction which makes separating the two different sets of data in the graph on the basis of the colour of the lines quite easy.

This type of approach is not ideal, the sampling interval for the extracted data is not uniform, and not the same for the two datasets, furthermore the labelling of the x-axis is unclear so it’s difficult to tell exactly which quarter is referred to.

I next loaded up the data into Excel for a bit of quick and easy plotting. To address the sampling problem I used the vlookup function to give me data for each series on a quarterly basis. I can then plot interesting things like the difference between the current and original estimates for each quarter, as shown below:

A few spot checks referring back to the original chart can convince us that we have scraped the original data moderately well. The data also fit with the ONS comment on the article:

…looking back over the last 20 quarters, between the first and most recent estimates, the absolute revision (that is, ignoring the +/- sign) is still only 0.4 percentage points.

I calculated this revision average and got roughly the same result.We can also plot the size of revisions made as a function of the current estimate of the GDP growth figure:

This suggests that as the current estimate of growth goes up so does the size of the revision: rises are under-estimated, falls in growth are under-estimated in the first instance although this is not a statistically strong relationship. These quarterly figures on GDP growth seem awfully noisy, which perhaps explains some of the wacky explanations for them (snow, weddings, hot weather etc etc) – they’re wild stabs at trying to explain dodgy data which doesn’t actually have an explanation.

The thing is that the “only 0.4 percentage points” that the ONS cites makes all the difference between being in recession and not being in recession!

Footnotes

I uploaded my spreadsheet here, the figures did not import well.

Continue reading »]]> This post is a review of “Stargazers:The Life and Times of the Telescope” by Fred Watson. It traces the history, and development of the telescope from a little before its invention in 1608 to the present day.

The book begins its historical path with Tycho Brahe, a Danish astronomer who lived 1546-1601. He built an observatory, Uraniborg, on the Danish island of Hven in view of his patron, King Frederick II of Denmark. Brahe’s contribution to astronomy were the data which were to lead to Johannes Kepler’s laws of planetary motion and ultimately Isaac Newton’s laws of gravitation. On the technical side his observatory represented the best astronomy of pre-telescope days with the use of viewing sights, his Great Armillary with it axis aligned with that of the earth and graduated scales to measure angles. Watson also cites him as a first instance of a research director running a research institute – alongside the observatory he ran a print works to disseminate his results.

The telescope was first recorded in September of 1608, when Hans Lipperhey presented one to Prince Maurice of Nassau in the Netherlands. Clearly it was a device of its time since in very short order several independent inventions appeared, Galileo constructed his own version which led to his publication of “The Starry Messenger” in 1610 which reports his observations using the device. The telescope grew out of the work of spectacle makers; there are some hints of the existence of telescope-like devices in the latter half of the 16th century but these are vague and unsubstantiated. Roger Bacon and Robert Grosseteste both conceived of a telescope-like device in the 13th century, around the time the first spectacles were appearing. Although there are a few lenses from antiquity there is no good evidence that they had been used in telescopes.

The stimulus for the creation of the first telescopes seems to have been a combination of high quality glass becoming available, and skilled lens grinders. The lens making requirements for telescopes are much more taxing than for spectacles. The technology required is not that advanced, if you look around the web you’ll find a community of amateur astronomers grinding their own lenses and mirrors now using fairly simple equipment, typically a turntable with a secondary wheel which produces linear motion for the polishing head back and forward across the turning lens blank. The most technologically advanced bit is probably captured in the first step: “acquire your glass blank”.

Through the 17th century refracting telescopes were built of ever greater length in an effort to defeat chromatic aberration which arises from the differential refraction of light as a function of wavelength (colour) – long focal length lenses suffered from less chromatic aberration than the shorter focal length ones which would allow a shorter telescope. Johannes Hevelius made telescopes of 46m focal length (physically the telescope would be a little shorter than this), mounted on a 27m mast; Christiaan Huygens dispensed with the “tube” of the telescope entirely and made “aerial telescopes” with even longer focal lengths, up to 64m.

It was known through the work of Alhazen in the 10-11th century, and others, that reflecting, curved-mirrors could be used in place of lenses. A telescope constructed with such mirrors would avoid the problem of chromatic aberration. However, the polishing tolerances for a reflecting telescope are four times higher than that of a lens. Newton built the first model reflecting telescope in 1668 but no-one was to repeat the feat until John Hadley in 1721.

Theoretical understanding of telescopes developed rapidly in the 17th century both for refracting and reflecting telescopes, indeed for reflecting telescopes there were no fundamental advices in the theory between 1672 and 1905. The problem was in successfully implementing theoretical proposals. Newton claimed that chromatic aberration could not be resolved in a refracting telescope, however he was proved wrong by Chester Hall Moor in 1729, and somewhat controversially by John Dollond in 1758 who was able to obtain a patent despite this earlier work (which was defended aggressively by his son) – the trick is to build compound lenses comprised of glass of different optical properties.

Also during the 18th century the construction of reflecting telescopes became more common, William Herschel started building his own reflecting telescopes in 1773 with the aid of Robert Smith’s “Compleat system of opticks”. Ultimately he was to build a 40ft (12m) telescope with a 48 inch (1.2m) mirror in 1789, supported by a grant from George III. During his lifetime Herschel was to discover the planet Uranus (nearly called George in honour of his patron), numerous comets and nebulae. At the time “official” astronomy was more interested in the precise measurement of the positions of stars for the purpose of navigation. Herschel was to be followed by Lord Rosse with his 1.8m diameter mirror telescope built in 1845 at Birr Castle, this has been recently restored (see here). He too was interested in nebula and discovered spiral galaxies.

During the 19th century there were substantial improvements in the telescope mounts, with engineers gaining either an amateur or professional interest (men such as James Nasmyth and Thomas Grubb). Towards the end of the century photography became important, which placed more exacting standards for telescope mounts because to gain maximum benefit from photography it was necessary to accurately track stars as they moved across the sky to enable long exposure times. This is also the century in which stellar spectrography became possible with William Huggins publishing the spectra of 50 stars in 1864. Léon Foucault invented the metal coated glass mirror in 1857 which were lighter and more reflective than the metal mirrors used to that point. As the century ended the largest feasible refracting telescopes with lens diameters of 1m were just around the corner, above this size a lens distorts under its own weight reducing the image quality.

In 1930 Bernhard Schmidt designed a reflecting telescope which avoided the problem of aberrations away from the centre of the field of view making large field of view “survey” telescopes practicable. As a youth in the 1970s I learnt of the 200-inch (5 metre) Hale telescope at Mount Palomar, since then space telescopes able to see in the infra-red and ultra-violet as well as the visible have escaped the distortion the atmosphere brings; adaptive optics are used to counteract atmospheric distortion for earthbound telescopes and there are “distributed” interferometric telescopes which combine signals from several telescopes to create a virtual one of unfeasible size.

Watson mentions briefly radio telescopes and in the final chapters speculates on developments for the future and gravitational lensing – natures own telescopes built from galaxies and spread over light years.

I enjoyed “Stargazers” as a readable account of the history of the telescope which left me with a clear understanding of its principles of operation and the technological developments that enabled its use, it also provides a good jumping off point for further study.

Footnotes

My Evernotes for the book are here, featuring more detailed but slightly cryptic notes and links to related work.

Continue reading »]]>

Bullied teachers fear culture of ‘macho managers’. Union survey shows 67% were affected by abuse and harassment from their colleagues

The Observer 08.04.12

This is the headline and subtitle to an article in The Observer today. Sound terrible doesn’t it? If I were working in an organisation where 67% of the staff were being bullied I’d probably want to leave, and I’d certainly expect senior management to be addressing the problem. Fortunately I suspect this headline is almost entirely misleading.

Firstly, the first line of the article says “more than two-thirds of teachers have experienced or witnessed workplace bullying in the past 12 months” (my emphasis) – so one teacher shouting at a colleague in a busy staffroom would generate an awful lot of “yes” votes.

Secondly, it’s described as an “online poll”, giving no information on the nature of the poll. If the respondents are randomly selected then fine, however if they are self-selected then it’s close to meaningless.

It’s possible that the level of bullying of teachers by their colleagues is at the level implied by the headline, but they’ve been done a great dis-service by their union and The Observer in the poor example of polling and reporting.

You’d have thought The Observer would have learnt its lesson by now, having published a mea culpa “When is a poll not a poll?” over a headline claiming “Nine out of 10 members of Royal College of Physicians oppose NHS bill” which highlighted exactly the issue with self-selecting surveys.

Continue reading »]]> It’s been a while since I did a data driven blog post, so here I am with one on the “Board of Longitude”. The board was established by act of parliament in 1714 with a headline prize of £20,000 to anyone who discovered a method to determine the longitude at sea to within 30 nautical miles. The members of the Board also had discretion to make smaller awards of up to £2,000 in support of proposals which they thought had merit. The Board was finally wound up in 1828, 114 years after its formation.

The latitude is your location in the North-South direction between the equator and either of the earth’s poles, it is easily determined by the position of the sun or stars above the horizon, and we shall speak no more of it here.

The longitude is the second piece of information required to specify ones position on the surface of the earth and is a measure your location East-West relative to the Greenwich meridian. The earth turns at a fixed rate and as it does the sun appears to move through the sky. You can use this behaviour to fix a local noon time: the time at which the sun reaches the highest point in the sky. If, when you measure your local noon, you can also determine what time it is at some reference point Greenwich, for example, then you can find your longitude from the difference between the two times.

The threshold for the highest Longitude award amounts to knowing the time at Greenwich to within 2 minutes, wherever you are in the world, and however you got there. This was a serious restriction at the time, because a journey to anywhere in the world could have taken months of voyaging at sea with its concomitant vibrations and extremes of temperature, pressure and humidity all of which have serious implications for precision timekeeping devices.

The Board of Longitude intertwines with various of the people whose biographies I’ve read, and surveying efforts taking place during the 18th and 19th centuries. It made a walk on appearance in Tim Harford’s Adapt, which I’ve just read, as an early example of prizes being offered to solve scientific problems.

Below I present data on the awards made by the Board during its existence from 1714 to 1828. The data I have used is from “Britain’s Board of Longitude: The Finances, 1714-1828” By Derek Howse¹ which I reached via The Board of Longitude Project based at the Royal Museums at Greenwich. The chart below shows the cumulative total of the awards made by the Board (blue diamonds), awards made to John Harrison who won the central prize of the original Board (black triangles) and the dates of Acts of Parliament relating to the Board (red squares). Values are presented as at the time they were awarded, the modern equivalent values are debatable but the original £20,000 award is said to have been worth between £1million and £3.5million in modern terms, so a rule of thumb would be to multiple by 100 to get approximate modern values.

Although established in 1714, the Board made no reward until 1737 and until 1765 made the great majority of awards to John Harrison for his work on clocks; clockmakers Thomas Earnshaw (1800, 1805), Thomas Mudge (1777,1793) and John Arnold (father and son 1771-1805) also received significant sums from the Board.

A second area of awards was in the “lunar” method of determining the longitude which uses the positions of stars relative to the moon to determine time and hence longitude. The widow of Tobias Mayer received the largest award, £3,000, for work in this area. The list of awardees contains a number of famous European mathematicians including Leonhard Euler, Friedrich Bessel, and Johann Bernoulli. 

After 1763 the Board started to branch out, having been mandated by parliament to prepare and print almanacs containing astronomical information. In the twilight of its years the Board gained responsibility for awards relating to the discovery of the North-West passage (a sea route from the Atlantic to the Pacific via the north of Canada), the second largest recipient of awards for the whole period were the crews of the Hecla and Griper of £5000 in 1820 for reaching 110^oW within the Arctic Circle, pursuing this goal.

The story of the Board of Longitude is often presented as a battle between the Board and John Harrison for the “big prize” but these data highlight a longer and more subtle existence with Harrison receiving support over an extended period and the Board going on to undertake a range of other activities.

References

1. “Britain’s Board of Longitude: The Finances, 1714-1828” By Derek Howse, The Mariner’s Mirror, Vol. 84(4), November 1998, 400-417. (pdf) Sadly the article notes that Derek Howse died after the preparation of this article.

2. Data from (1) can be found in this Google Docs spreadsheet

Continue reading »]]> This is a review of “Adapt: Why Success Always Starts With Failure” by Tim Harford which puts forward the thesis that “trial and error” is the only way forward for complex endeavours to succeed.

Opening up to trial and error is divided into three tasks:

• Providing scope for variation in what you do;
• Establishing whether or not a variant has been successful;
• Making sure that you have systems in place to cope with failure.

Each of these tasks is illustrated with a wide range of real-life examples: using the Iraq War to highlight the difficulties of running “trial and error” inside control structures that are designed to take in information, channel it to the top of the organisation and provide a channel back from the top to the bottom. Donald Rumsfeld, apparently, would not refer to the “insurgents” as “insurgents” so hobbling the US’s ability to fight an “insurgency”.

Alongside these major case studies are smaller ones, such as on Jamie Oliver’s school dinners which showed that feeding children healthy food at primary level led to measurably better outcomes in education and attendance than comparable groups not within the scheme, you can see the study here.

There is also a section on using a carbon tax to address anthropogenic climate change, this fits in as a way of making selection possible by providing a simple measure of “success”. Harford is scathing of the ”Merton Rule” which demands that new build of above a certain size generate 10% of their electricity onsite by renewable means. As put by Harford this means installing capacity rather than demonstrating capacity which has lead to the use of dual fuel systems (nominally able to take renewable fuel) that are ultimately only used with non-renewables so providing no benefit at all.

The Piper Alpha and Three Mile Island accidents are provided as examples of the importance of being able to fail safely, they didn’t or rather Piper Alpha didn’t – arguably Three Mile Island just about failed safely. This was linked to failings in the financial system where large organisations, such as Lehman Brothers failed in a matter of hours with administrators scrabbling around frantically to come up with a controlled-landing plan. This is failure at large scale, but there is also coping with failure at the personal scale. For example, using “Deal or No Deal” as a model system in which contestants can “lose” which changes their estimations of risk for subsequent play for the worse.

One issue with “trial and error” is that the proponents of any method are often so convinced of the value of their method that they feel it immoral to subject anyone to an “inferior” alternative in order to conduct a trial. This is highlighted with a story about Archie Cochrane, pioneer of the randomised control trial in medical studies. He had been running a study on coronary care, comparing home-based care to hospital care. This had met with some opposition, with medics insisting that the home-based arm of the trial was unethical because it was bound to be inferior. When results started to come in it turned out that one branch of the trial was inferior to the other – Cochrane misled his colleagues into believing it was the home-based arm that was inferior – they demanded that it should be closed down but were rather silent when he revealed that it was in fact the hospital-based arm of the trial that was inferior!

Harford also discusses funding for research, in particular that blue-skies research could not be valued because the outcomes were so uncertain, highlighting the success of the Howard Hughes Medical Institute which funds speculative biomedical research in the US. What he goes on to say is that the use of prizes is a way out of this impasse. Using as an example the Longitude Prizes, his presentation plays up the friction between Harrison and the Board of Longitude. The Academie Des Sciences also ran prizes but until recently the method had been out of favour for approaching 200 years. The recent revival has included things like the DARPA challenges for self-driving cars, Ansari X Prize, the Bill and Melinda Gates Foundation prize for vaccines and Netflix’s film selection challenge. These have been successful, however it’s difficult to see them finding more general favour in the academic community since the funding is uncertain and appears only after researchers have expended resources rather than receiving the resource before doing the work.

From a practical point of view “trial and error” happens in the private sector, if not within companies then between. In the voluntary sector it has taken some hold, for me some of the more compelling examples were by the “randomistas” studying the effectiveness of aid programmes. In the public sector “trial and error” is more difficult: there is less scope for feedback on the success of a trial – you can’t meaningfully count customers through the door, or profits made, so there is a need for proxy measures. Furthermore, the appearance of failure carries a high price in the political sphere. This is not to say it shouldn’t happen, simply that “trial and error” face particular challenges in this area.

I like the central thesis of the book, it fits with my training as a scientist; my field allows for more direct experimentation than a randomised trial but the principle is the same. It also has pleasing parallels with biological evolution, which Harford explicitly draws. The book is well referenced, in fact I hit the end unexpectedly as I was reading on a Kindle – I couldn’t “see” the length of the end notes!