Tag: astronomy

Book review: The First Astronomers by Duane Hamacher

My next review is of First Astronomers: How Indigenous Elders read the stars by Duane Hamacher. It is fair to say that Western astronomers, and other Western scientists have not treated Indigenous populations, and their knowledge, with a great deal of respect. Even now astronomers are in dispute with Indigenous populations in Hawaii over the siting of telescopes. In this book Hamacher tries to redress this imbalance and in my view does a good job of treating his interviewees, and their knowledge, with respect.

Western astronomers are not alien to interacting with people outside their professional group as part of their research most notably using historical data, like Chinese records of supernova but also amateur observers play an important in modern astronomy – particularly in the observation of comets and the like and other transient phenomena accessible using modest equipment.

The book starts with a prologue describing the background to the book and introducing a number of the Indigenous people who contributed, in the longer frontspiece they are listed as co-authors. They are largely from Australia but there are references to New Zealand, North American Native Americans, Artic peoples, South American and Africa groups.

Hamacher is an astronomer by profession and this has a bearing on this interviews with Indigenous Elders. In the past anthropologists have talked to Elders about their star knowledge and a lack of astronomical knowledge has led to mis-interpretation. I was intrigued to learn that in Western mythology the star name “Antares” is derived from the greek “anti Mars” – since Mars and Antares, in the same part of the sky and with a reddish hue are often confused!

The book is then divided thematically into chapters relating to different sorts of stars (including the moon). These are The Nearest Star (the sun), The Moon, Wandering Stars (planets), Twinkling Stars, Seasonal Stars, Variable Stars, Cataclysmic Stars (supernova and the like), Navigational Stars and Falling Stars (meteors and craters).

The big difference a Western reader will see is that Indigenous knowledge is transmitted via oral traditions, incorporating song and dance. Oral traditions are about creating a story around some star locations that provide useful information like where and when to hunt a particular animal or plant a particular crop, or where you are and how to get to where you want to be . The story linked to the stars allows it to be transmitted to the next generation without error. They are mnemonics rather than an attempt to describe a factual truth. This is obvious in Indigenous oral traditions which are still alive but I suspect it would have been the case for the oral traditions of Western Europe which give us our modern constellations.

Oral traditions can be very powerful, there is a group of craters in Australia (the Henbury Craters) which were created by a meteor impact around 4200 years ago – Aboriginal oral traditions have held this knowledge of their creation across that period of time.

Indigenous constellations can overlap and change through the seasons, they also incorporate dark space – particularly in the Milky Way. These constellations are locally determined to fit with local conditions, and land features used as landmarks.

As well as maritime navigation where the stars are used directly for finding direction, the stars are also used as a navigational aid for terrestrial travel – the routes are learnt in the dark of the winter using the stars as a map of the ground (picking stars which approximate the locations on the ground). These “songlines” are reflected in some modern day highways in Australia.

What comes through from the book is that Indigenous astronomers were very astute observers of the sky, noting phenomena including the varying twinkle of stars (including colour and intensity variations), the 8 year period of Venus returning to the same location in the sky, variable stars, sunspots and their 11 year cycle, the sounds associated with aurora and so forth. Some of these phenomena were not widely recognised by astronomers in the West until into the 19th century. In addition they had a clear understanding of many phenomena: that the moon reflected the light of the sun, that the earth was a sphere, that craters were the result of rocks falling from the sky.

Unsurprisingly, I was constantly comparing with Western astronomy. The great divergence was sometime around the end of the 16th century when Western astronomers started making detailed written records of the locations of stars and planets and using mathematics to understand them, and then moved on to the use of telescopes. I can’t help feeling the Indigenous people were held back by a lack of writing.

What comes through at the end of the book is that in the Indigenous communities have a long history of passionate and astute astronomers, dedicated to their role, and increasingly they are taking part and excelling in Western astronomy and astrophysics.

Book Review: Stargazers–Copernicus, Galileo, the Telescope and the Church by Allan Chapman

stargazersIt’s been a while since my last book review here but I’ve just finished reading Stargazers: Copernicus, Galileo, the Telescope and the Church by Allan Chapman.

The book covers the period from the end of the 16th century, the time of Copernicus and Tycho Brahe, to the early 18th century and Bradley’s measurement of stellar aberration passing Galileo, Newton and others on the way. Conceptually this spans the full transition from a time when people believed in a Classical universe with earth at its centre, and stars and planets plastered onto crystal spheres, to the modern view of the solar system with the earth and other planets orbiting the sun.

This development parallels that in Arthur Koestler’s classic book "The Sleepwalkers”, however Chapman’s style is much more readable, his coverage is broader but not so deep. Chapman introduces a wealth of little personal anecdotes and experiments. For instance on visiting Tycho Brahe’s island observatory he recounts a meeting with a local farmer who had in his living room a marked stone from the Brahe’s observatory (which had been dismantled by the locals on Brahe’s death). Brahe was hated by his tenants for his treatment of them, a hate that was handed down through the generations. Illustrations are provided in the author’s own hand, which is surprisingly effective. He discusses his own work in reconstructing historical apparatus and observations.

Astronomy was an active field from well before the start of this period for a couple of reasons: firstly, astrology had been handed down from Classical times as a way of divining the future. To was believed that to improve the accuracy of astrological predictions better data on the locations of heavenly bodies over time was required. Similarly, the Christian Church required accurate astronomical measurement to determine when Easter fell, across increasingly large spans of the Earth.

The period covered by the book marks a time when new technology made increasingly accurate measurements of the heavens possible, and the telescope revealed features such as mountains on the moon, sunspots and the moons of Jupiter visible for the first time. Galileo was a principle protagonist in this revolution.

Amongst scientists there is something of the view that the Catholic Church suppressed scientific progress with Galileo the poster boy for the scientist’s case. Historians of science don’t share this view, and haven’t for quite some time. Looking back on Sleepwalkers, written in 1959 I noted the same thing – the historians view is generally that Galileo brought it on himself in the way he dismissed those that did not share his views in rather offensive terms. Galileo lived in a time when the well-entrenched Classical view of the universe was coming under increased pressure from new observations using new instruments. In some senses it was the collision with the long-held Classical view of the universe which led to his problems, the Church being more committed to this Classical view of the physical universe rather than to anything proposed in Scripture.

The role of the Church in promoting, and fostering science, is something Chapman returns to frequently – emphasising the scientific work that members of the Church did, and also the often good relationships that lay “scientists” of different faiths had with Church authorities.

Chapman introduces some of the lesser known English (and Welsh) contributors to the story. Harriet who made the earliest known sketches of the moon. The Lancashire astronomers, who made the first observations of the transit of Venus. John Wilkins whose meetings were to lead to the foundation of the Royal Society. He also notes the precedent of the Royal College of Physicians, formed in 1518. The novelty of the Royal Society when compared with earlier organisations of similar character was that the Fellows were responsible for new appointments, rather than them being imposed by a patron. This seems to have been an English innovation, repeated in the Oxbridge colleges, and Guilds.

Relating to these English astronomers was the development of precision instruments in England. This seems to have been spurred by the Dissolution of the monasteries. The glut of land, seized by Henry VIII, became available to purchase. The purchase of land meant a requirement for accurate surveying, and legal documents. Hence an industry was born of skilled men wielding high technology to produce maps.

I was distracted by the presence of Martin Durkin in the acknowledgements to this book, he was the architect of “polemical” Channel 4 documentary “The Great Global Warming Swindle”, so it cast doubt in my mind as to whether I should take this book seriously. On reflection Chapman’s position as presented in this book seems respectable, but it is interesting how a short statement in the acknowledgements made me consider this more deeply.

Overall, Stargazers is rather more readable than Sleepwalkers, not quite so single-tracked in it’s defence of the Catholic Church as God’s Philosophers and a different proposition to Fred Watson’s book of the same name, which is all about telescopes.

…when the sun is eclipsed by the moon

Friday 20th March 2015 saw a solar eclipse visible over the British Isles, subject to the vagaries of the British weather. I have some form in taking pictures of the sun through my telescope. With solar eclipses taking place in the UK only once every 10 or so years (the last one was in 1999), I thought it worth the effort to take some pictures.

The key piece of equipment was the Baader AstroSolar filter mount I made a while back. It’s designed to fit on my telescope but works pretty well for naked-eye viewing and with my Canon 600D camera. I used a Canon 70-300m lens, mainly at the maximum zoom with varying exposure parameters depending on cloud. I used autofocus in the main but manually set exposure time, aperture and ISO. Consumer cameras aren’t designed to give good auto exposure for usual activities such as eclipse observations.

Here’s a closeup of the filter:


The uninitiated may not be impressed by the finish on this piece of equipment but as a scientist of 20 years standing I’m happy to report that I’ve had plenty of stuff in my lab in similar style – it’s good enough to do the job.

Solar eclipses last a surprisingly long time, this one was a little over two hours with first contact of the moon on the suns disk at 8:26am in Chester. This photo was taken at 8:26am, you can just see the moon clipping the edge of the sun top right.


By 9:01am things were well under way. The birds had started their evening song around this time and it was starting to feel unusually dark for the time of day.


The maximum of the eclipse was at 09:30am, by this time clouds had appeared and I used them as an ad hoc solar filter.


By 09:50am we were well past the maximum:


The last photo I managed was at 10:18 before the sun disappeared behind the clouds:


Finally, this is a collage of the majority of pictures I took – some of them are pretty rough:

010 - Eclipse - 20mar151

Messier and messier

Regular readers with a good memory will recall I bought a telescope about 18 months ago. I bemoaned the fact that I bought it in late Spring, since it meant it got dark rather late. I will note here that astronomy is generally incompatible with a small child who might wake you up in the middle of the night, requiring attention and early nights.

Since then I’ve taken pictures of the sun, the moon, Jupiter, Saturn and as a side project I also took wide angle photos of the Milky Way and star trails (telescope not required). Each of these bought their own challenges, and awe. The sun because it’s surprisingly difficult to find the thing in you view finder with the serious filter required to stop you blinding yourself when you do find it. The moon because it’s just beautiful and fills the field of view, rippling through the “seeing” or thermal turbulence of the atmosphere. Jupiter because of it’s Galilean moons, first observed by Galileo in 1610. Saturn because of it’s tiny ears, I saw Saturn on my first night of proper viewing. As the tiny image of Saturn floated across my field of view I was hopping up and down with excitement like a child.

I’ve had a bit of a hiatus in the astrophotography over the past year but I’m ready to get back into it.

My next targets for astrophotography are the Deep Sky Objects (DSOs), these are largish faint things as opposed to planets which are smallish bright things. My accidental wide-angle photos clued me into the possibilities here. I’d been trying to photograph constellations, which turn out to be a bit dull, at the end of the session I put the sensitivity of my camera right up and increased the exposure time and suddenly the Milky Way appeared! Even in rural Wales it was only just visible to the naked eye.

Now I’m keen to explore more of these faint objects. The place to start is the Messier Catolog of objects. This was compiled by Charles Messier and Pierre Méchain in the latter half of the 18th century. You may recognise the name Méchain, he was one of the two French men who surveyed France on the cusp of the Revolution to define a value for the meter. Ken Alder’s book The Measure of All Things, describes their adventures.

Messier and Mechain weren’t interested in the deep sky objects, they were interested in comets and compiled the list in order not to be distracted from their studies by other non-comety objects. The list is comprised of star clusters, nebula and galaxies. I must admit to being a bit dismissive of star clusters. The Messier list is by no means exhaustive, observations were all made in France with a small telescope so there are no objects from the Southern skies. But they are ideal for amateur astronomers in the Northern hemisphere since the high tech, professional telescope of the 18th century is matched by the consumer telescope of the 21st.

I’ve know of the Messier objects since I was a child but I have no intuition as to where they are, how bright and how big they are. So to get me started I found some numbers and made some plots.

The first plot shows where the objects are in the sky. They are labelled, somewhat fitfully with their Messier number and common name. Their locations are shown by declination, how far away from the celestial equator an object is, towards the North Pole and right ascension, how far around it is along a line of celestial latitude. I’ve added the moon to the plot in a fixed position close to the top left. As you can see the majority of the objects are North of the celestial equator. The size of the symbols indicates the relative size of the objects. The moon is shown to the same scale and we can see that a number of the objects are larger than the moon, these are often star clusters but galaxies such as Andromeda – the big purple blob on the right and the Triangulum Galaxy are also bigger than the moon. As is the Orion nebula.


So why aren’t we as familiar with these objects as we are with the moon. The second plot shows how bright the Messier objects are and their size. The horizontal axis shows their apparent size – it’s a linear scale so that an object twice as far from the vertical axis is twice as big. Note that these are apparent sizes, some things appear larger than others because they are closer. The Messier The vertical axis shows the apparent brightness, in astronomy brightness is measured in units of “magnitude” which is a logarithmic scale. This means that although the sun is roughly magnitude –26 and the moon is roughly magnitude –13, the sun is 10,000 times bright than the moon. The Messier objects are all much dimmer than Venus, Jupiter and Mercury and generally dimmer than Saturn.



So the Messier objects are often bigger but dimmer than things I have already photographed. But wait, the moon fills the field of view of my telescope. And not only that my telescope has an aperture of f/10 – a measure of it’s light gathering power. This is actually rather “slow” for a camera lens, my “fastest” lens is f/1.4 which represents a 50 fold larger light gathering power.

For these two reasons I have ordered a new lens for my camera, a Samyang 500mm f/6.3 this is going to give me a bigger field of view than my telescope which has a focal length of 1250mm. And also more light gathering power – my new lens should have more than double the light gathering power!

Watch this space for the results of my new purchase!

Book review: The Sleepwalkers: A History of Man’s Changing Vision of the Universe by Arthur Koestler

Sleepwalkers_ArthurKoestler.Another result of my plea for reading suggestions on twitter; this is a review and summary of Arthur Koestler’s book “The Sleepwalkers: A History of Man’s Changing Vision of the Universe”. The book is a history of cosmology running from Pythagoras, in the 6th century BC, to Galileo who spanned the end of the 16th century, just touching lightly on Newton. It traces a revolution from a time when the cosmos, beyond the earth, was considered different, stable and perfect, to a time when it was shown to be subject to earthly physics, be changeable and not perfect by any reasonable definition.

Kuhn’s language of paradigm shifts seems rather overused to me but here is an example of a true paradigm shift. The sleepwalkers in the title refers to the idea that the protagonists didn’t really know where they were headed with their ideas and quite often were lucky with errors which cancelled each other out.

The book starts with a cursory look at Babylonian and early Greek astronomy; despite considerable observational acumen their models of the universe were outright mythical. The Pythagoranean Brotherhood although in many senses still mystical started to think about the physics of the universe. I have a tendency to think of the ancient Greeks as one blob but as the book makes clear there is a huge span of time, and outlook, between Pythagoras, Aristotle and Plato and Ptolemy. Koestler is quite clearly disappointed with the Greeks: they make a promising start with Pythagoras, Aristarchus developed a heliocentric model for the solar system and then with Plato, Aristotle and Ptolemy they regress back to a geocentric model.

Following on from the Greeks the Middle Ages are covered, James Hannam in his book “God’s Philosophers” has covered why this period wasn’t all that bad in terms of intellectual development. Koestler is less sympathetic, his key accusations are that they philosophers of the middle ages were in thrall to the later Greeks and furthermore there were elements of Christian theology that abjured the pleasure of knowledge for knowledge’s sake.

After these preliminaries, Koestler turns to the core of his work: the cosmological developments of Copernicus, Tycho Brahe, Johannes Kepler and Galileo Galilei.

The model of the universe handed down from the ancient Greeks was one of circles (often referred to in this context as epicycles), they believed that motion in a circle was perfect, that the heavens were a separate, perfect realm and that therefore all motion in the heavens must be based on circular motion. Further, the model dominating at the end of their period, held that the earth lay at the centre of these circular motions. The only problem with this model is that it doesn’t fit well the observed motions of the sun, moon, Mercury, Venus, Mars, Jupiter and Saturn – the observable solar system which lay against an unchanging starry background. Or rather you can get a rough fit at the expense of stacking together a great number of epicycles – something like 50.

Copernicus’ contribution, published on his death in 1543, was to put the sun back at the centre of the universe. Copernicus led a rather uneventful life, was no sort of astronomical observer and only published his thesis at the end of his life at the strong urging of Georg Joachim Rheticus. He’d discussed his model fairly freely during his life, and his reasons for not publishing were more to do with fear of ridicule from his contemporaries rather than theological pressure. After his death his work, with the exception of the astronomical tables, sank into obscurity partly because it was a difficult read and partly because he managed to ostracise his former cheerleader, Rheticus. Copernicus’ model still holds to the epicycles of the Greeks, and only marginally reduces the complexity of the model.

Next up comes Johannes Kepler, interspersed with Tycho Brahe. Brahe was an astronomical observer and nobleman, funded very well by the Danish king; given his own island Hveen where he built his observatory. As a keen astrologer he began his observation programme when he found a conjunction of Jupiter and Saturn was poorly predicted by current astronomical tables – how can you cast an accurate fortune under these circumstances?

Kepler was a theoretician rather than an observer but also a keen astrologer. I emphasise this because these days astrology is not held in high regard but it is the father of observational astronomy. He had started to develop a model of the solar system based on the Platonic solids – something of a mystical exercise but realised he needed better data to support his model. Brahe was the man with the data, Kepler was only just in time though – he travelled to work with Brahe when Brahe moved to Prague less than 2 years later Brahe was dead. Nowadays we know Kepler for his three laws of planetary motion – it’s worth noting that Kepler’s laws are labelled retrospectively.)

He left copious records of his progress which Koestler traces in great detail, Kepler’s struggle to recognise that planetary orbits were ellipses was heroic and has something of a pantomime air to it – “They’re right in front of you!”. His approach was unprecedented in the sense that he sought to accurately model the very best, most recent measurements. Kepler also made some attempts at a physical model to describe the motions but ultimately he is remembered for the detailed description of their motion. Since it is not central to his theme, Koestler makes only passing reference to Kepler’s work on optics.

The penultimate figure in the story is Galileo, despite Kepler’s best efforts Galileo pretty much ignored him. Galileo gets quite short shrift from Koestler who feels that he brought his troubles with the Catholic Church upon himself. Reading this account his position is not unreasonable. Galileo’s two big contributions to the story are his promotion and use of the telescope, and his work on the motion of terrestrial bodies, the generalisation of which and application to the solar system was Newton’s great triumph. Cosmologically he was only later in his life a supporter of the somewhat retro Copernican model which was a cul-de-sac in terms of theoretical developments. At the time the Catholic Church, particularly the Jesuits, were interested in astronomy and not particularly hardline about the interpretation of Scripture to fit observations. Galileo wound them up both by claiming all newly observed celestial phenomena as his own and by putting the words of the Pope in the mouth of an idiot in one of his Dialogues.

This highlights two of the wider themes that Koestler brings to his book. At one point he describes his cast of characters as “moral dwarves”, he states this is relative to their scientific achievements but returns to this theme in the epilogue where he feels that our scientific developments have not been matched by our spiritual development. The second is the schism between science and the Church that began in this period, Koestler seems to put much of the blame for this on Galileo’s head feeling that it is by no means inevitable. In the epilogue he also draws a comparison between biological evolution and scientific developments, highlighting specifically that there are long periods of not that much happening and many diversions from the “true” path.

The book finishes with a brief mention of Newton’s synthesis of Kepler’s laws and Galileo’s dynamics to produce a model of the solar system which is close to that which we hold today.

This really is a rollicking good read! This is a relatively old book, published in 1959 and one might anticipate that it has not fully caught up with modern historiography however a brief look around the internet suggests that he is not criticised in any great sense. Koestler does tend to focus on a limited number of “great” individuals and goes for “firsts” but this perhaps is what makes it a good read.


My Evernotes for the book are here, last page of the book at the top!