A tennis court guide to the Solar System

When thinking about astronomy it is sometimes very difficult to visualise just how big distances are between objects, and also how they compare in size.

For example, we know that the Sun is vastly bigger than Planet Earth, but just how much bigger? The answer is 109 times, in terms of diameter. Or, to put it another way, if the Sun was the size of a tennis ball, Earth would be the size of a piece of grit half a millimetre across!

OK – so if we stick with the idea of the Sun as a tennis ball, which you can easily visualise being held by a tennis player who is about to serve at the start of a game, where would the piece of grit that we live on have to be placed to be the same scale? The answer is 12.5 metres or 41 feet away, which would get the ball over the net. If, when playing tennis, you can spot an object of that size in the service court on the other side of the net, you must have excellent eyesight!

The distance from the Sun to the Earth is known as the Astronomical Unit, because it is a useful measure for making comparisons. The outermost planet is Neptune (now that Pluto has been “demoted”). This would be about the size of a small cake-decoration silver ball on our scale, but at 30 astronomical units from the Sun it is unlikely to be visible by even the keenest-eyed tennis player standing on the baseline!

If you were to place 16 tennis courts end to end, our player would serve a fault on the 16^th court if his serve managed to reach silver ball Neptune! 

© John Welford

The Tailor, by Giovanni Moroni

Giovanni Battista Moroni (c.1520-78) was a painter, mostly of portraits, who worked in the northern Italian cities of Brescia, Bergamo, Trento and Albino. His early works were mainly full-length lifesize portraits of local noblemen, but in his later years, spent mostly in his birth town of Albino, he developed a more intimate style in which the aim was not to glorify the sitter but to convey their personality. “The Tailor”, dating from around 1570, falls into the latter category.

The painting, which measures about 39 by 30 inches (100 by 77 cm), shows the subject standing at his workbench with his shears in one hand and a piece of dark cloth in the other. He is a youngish man, possibly in his mid-thirties, so he is well established in his trade and has the look of a confident professional businessman. He has clearly come far enough in his career to afford to have his portrait painted by such an eminent artist.

As a tailor, the subject clearly wants to be portrayed in clothing that befits both his status and his skill, assuming that he has made what he is wearing. This portrait was probably intended to be as much an advertisement for his wares as an accurate depiction of the tailor himself. He is wearing the typical dress of a prosperous man-about-town in 16^th century Europe, namely “doublet and hose”. The doublet was a close-fitting buttoned jacket with long sleeves and the hose was a padded garment that covered the area from waist to mid-thigh and was covered in vertical strips of material. These are sometimes referred to as “pumpkin pants” which would be worn over “under hose” that today would be called tights.

It is quite likely that these clothes would not have been what the tailor would normally have worn when at work. Just as the workbench is completely clear of any stray pieces of cloth or thread, the tailor is also seen in a deliberate pose that says: “this is what I am, this is what I do, and these are the clothes I make”.

Even so, the artist has done a lot more than merely produce an advertising poster. The tailor looks directly at the viewer as he turns his head slightly. It is almost as though he has been about to start work when somebody has come into his workshop but he has not had time to take in who they are. His glance is not unfriendly, but neither is it warm in the sense of breaking into a smile. This is very much a “snapshot” of a portrait, which is why it succeeds in being both intimate and revealing.

The lighting of the picture is cleverly done. The background is a blank grey wall, but a shaft of light falls across it from the top left-hand corner. This also lights the tailor’s face as he turns towards the viewer, thus giving it a realistic three-dimensional effect. The same applies to the details on the tailor’s doublet, where light and shade are used to indicate his slightly rounded stomach and convey the impression that this is not a man on the breadline but a prosperous artisan and trader who is well patronised.

The eye is taken by highlights of white on the tailor’s cuffs and belt, which are matched by the white of the small ruff at his neck. The way the arms are painted, being lit from the source mentioned above, also has the effect of leading the eyes upwards towards the tailor’s face, which is the painting's true focus. The viewer sees a man at work, but he/she is far more conscious of the man than of the work.

The composition of the painting thus gives the impression of simplicity and immediacy but the whole thing is a subtle arrangement of shapes and lighting effects that lead to a desired conclusion.

Although this is the work of an Italian painter, it seems to foreshadow the work of 17^th century Dutch painters such as Vermeer and De Hooch who would also take simple subjects from everyday life and elevate the ordinary into the extraordinary.

“The Tailor”, which is easily Moroni’s best-known work, is part of the permanent collection at the National Gallery, London.

© John Welford

Planet Earth's lopsided core

There is plenty of evidence to suggest that the core of Planet Earth consists mostly of iron (around 80%) with the rest probably being nickel, although there is some doubt about this. It is also thought that there is an inner core that is solid, surrounded by a liquid outer core. The vast amounts of iron at the centre of the Earth, and the convection currents in the outer core, cause the planet to have a magnetic field. This is profoundly important for life on Earth, because the magnetic field helps to shield the surface from harmful solar radiation. It also accounts for why compasses point to the Magnetic North Pole.

There is also evidence that points to the fact that compasses – had there been any around at the time – would have pointed to the Magnetic South Pole in past times. Samples of rock from extinct volcanoes show clearly that there have been periods in Earth’s history when the magnetic polarity has been the opposite of what it is now, and that there appear to have been many such switches in the past.

The last full switch in polarity occurred around 780,000 years ago, but there was a partial switch a mere 41,000 years ago. This was not a long-lasting arrangement, with the polarity returning to its previous state after only a few hundred years.

These switches do not seem to happen with any regularity, and it is impossible to predict when the next one will occur.

But why should such switches happen at all? One theory – which cannot be confirmed given our current knowledge – was proposed in 2012 by Peter Olson and Renaud Deguen who were working at Johns Hopkins University, Baltimore, Maryland, USA. They termed their theory “translational instability”.

The idea is that the iron at Earth’s core is not uniformly distributed but lopsided, with a greater amount having crystallised out on one side than the other during the cooling period after the initial formation of the planet.

When scientists speculate about what might have happened in the distant past, they build models (these days using computers) that can then suggest what the effects might be were their speculation to be correct. In this case, a lopsided iron core would – according to Olsen and Deguen’s model – cause the axis of any magnetic field to shift to the side where there was a greater concentration of iron. In turn, this would cause irregularities in the patterns of convection currents in the outer core, which would cause the polarity to switch from time to time.

The shifting position of the axis in the inner core could also – according to the theory – account for why Magnetic North is not the same as True North, and why the position of Magnetic North is not constant. Indeed, the shift in Magnetic North can be measured at around 35 miles (56 kilometres) per year, which is extremely rapid in geological terms.

Careful monitoring of the position of Magnetic North, and calculation of the speed of change, might be one way of determining when another polarity change is going to occur. Would that make a huge difference to how we live our lives? It would certainly mean that all navigation systems used by ships and planes would have to be revised, and it might also cause temporary chaos to communication systems, but otherwise the period of adjustment should not be too traumatic. It could, however, make life difficult for animals and birds that rely on Earth’s magnetic field for their migrations, but even they should be able to adjust before too long.

© John Welford

Mr and Mrs Clark and Percy, by David Hockney

David Hockney (born 1937) is by far the best-known and most critically acclaimed British artist of his generation. He is also highly regarded in the United States, where he was based for much of his life before returning to his native Yorkshire (albeit the coast at Bridlington rather than his birth-town of Bradford) in 2005.

Hockney has been an experimenter throughout his career, working with different styles and media and becoming as well-known for his graphic art as for his painting. He has also been highly successful as a photographer and a stage designer.

His “Mr and Mrs Clark and Percy” dates from 1970-71, with Hockney taking a full year to complete it. It was painted using acrylics on canvas and measures 305 by 213 centimetres (120 by 84 inches), thus making the subjects virtually life-size.

It is one of a series of double portraits made by Hockney at around that date, the subjects in this case being two people who were well known to him, the fashion designer Ossie Clark (1942-96) and fabric designer Celia Birtwell (born 1941). The couple had met at Salford College of Art in 1960, and David Hockney had known Clark since 1961. 

Clark and Birtwell worked together in a highly successful partnership from 1965 and were very much part of the “Swinging Sixties”, having a client list that included many of the leading figures in music and entertainment. They became lovers and their first son, Albert, was born in 1969. They married when Celia became pregnant with their second son, George, and Hockney was best man at the wedding.

The painting that Hockney began in 1970 therefore portrays his two friends in the early months of their marriage, with Celia showing signs of being pregnant, dressed elegantly in a purple dress with red trimmings. She stands, hand on hip, to the left of an open shuttered door that leads on to a brightly lit balcony on an upper floor of a London terraced house. To the right of the door sits Ossie, slightly slouched, on an office chair. His feet are bare and partly buried in the deep pile of a rug that extends across part of the floor. Percy, a white cat, sits perched on Ossie’s knee.

(It has since been pointed out that the cat is not actually Percy! The couple had two cats and the one in the painting is Blanche, but Hockney thought that “Percy” would sound better in the painting’s title)

It has long been the custom of portrait painters to surround the subject with items that say something about their work or what it is that makes them what they are. However, the viewer would be hard pressed to work out that this couple are just about the hottest thing in town as far as the fashion industry is concerned. Celia’s dress is elegant and functional, but it is not characteristic of either her textiles or Ossie’s designs.

Incidentally, it is interesting to compare this painting with Gainsborough’s “Mr and MrsRobert Andrews”, painted around 1748. The title of Hockney’s work may be a deliberate reference to the earlier work, which also features a young newly-wed couple, albeit with a dog instead of a cat.

The room is minimalist in its furnishing, which is not unsurprising for the time, but this means that few clues can be given that would distinguish this couple from millions of others. On a small plain white table there sits a slender vase of flowers (possibly artificial) and a yellow notebook. Behind Ossie, on the floor, is an ordinary dial telephone and an art deco-style lamp. The only item in the room that seems to betray any degree of lifestyle choice made by the couple is a print on the wall, which happens to be by David Hockney!

The focus therefore comes back to the painting’s subjects, and the somewhat disturbing conclusion, in the mind of the viewer, that they do not seem to be connected in any way apart from happening to be in the same room at the same time. One stands, the other sits; one is dressed formally, the other informally in trousers and a sweater; neither of them looks at the other but at the viewer. 

Percy (or Blanche) is likewise uninterested in either of the subjects, preferring to look out through the open door towards the sunlight. The viewer might also take the hint that the world outside this room has more to offer than this dull room occupied by two un-communicating people.

The impression that is conveyed, namely that these people have little to do with each apart from occupying the same space, no doubt comes in part from the circumstances under which Hockney constructed the painting. The couple posed separately in his studio, with Ossie’s pose being taken from a photograph of him having just got out of bed, which is why he has nothing on his feet. This latter fact may account for why Ossie has a cigarette between his fingers but there is no ashtray in sight; it would seem unlikely that Celia would approve of him dropping ash into the shagpile!

However, it has also been suggested that Hockney is using certain symbols to give other messages. The flowers next to Celia are lilies, which symbolise purity, whereas the cat, on Ossie’s knee, is a symbol of infidelity. At least, those are interpretations that some people accept. But there are other readings that can be made, such as the open doorway, with the sunlight streaming in, symbolising a rift between the couple.

At all events, the marriage did not last with the couple divorcing in 1974, although the two of them continued to have glittering careers in fashion (for a time; Ossie Clark later fell victim to drugs and was eventually murdered). Hockney knew that Ossie Clark was bisexual, and it is believed that the two had been lovers at some time during their friendship. Hockney therefore had a pretty good idea that this marriage was doomed, and clues in the painting are not difficult to spot.

Hockney made a present of the painting to the couple, and whether its message of ultimate separation was appreciated by them can only be guessed at. However, Hockney himself was of the view that the painting may have hastened the rift. He continued to be a good friend to both Celia and Ossie, with Celia posing for a number of portraits after the divorce.

The painting now hangs in Tate Britain, London, where it is one of the most popular of the gallery’s exhibits. In 2005 it was voted number 5 in the “Greatest Painting in Britain” poll held by BBC Radio 4, being the only painting by a living artist in the top ten.

© John Welford

Washington Crossing the Delaware, by Emanuel Gottlieb Leutze

“Washington Crossing the Delaware” is often seen as an iconic American image. However, it was not painted by an American, nor was it painted in America. It is also far from an accurate depiction of the event in question, because that was not the artist’s intention.

 Emanuel Gottlieb Leutze

Emanuel Gottlieb Leutze (1816-68) was born in Baden-Württemberg (now part of Germany) but emigrated with his family to the United States when he was nine years old. He trained as an artist and returned to Germany in 1841 to study at the Königliche Kunstakademie in Düsseldorf. He lived in Germany until 1859 when he settled again in the United States where he spent the rest of his life.

Leutze was inspired throughout his life by the principles of freedom and democracy which he saw embodied in the history of the United States, and much of his work as an artist was devoted to expressing those ideals on canvas. “Washington Crossing the Delaware” is a painting that embodies this motivation.

“Washington Crossing the Delaware”

It was painted in Germany in 1850, with a second version painted in 1851. It is this later painting that is currently exhibited in the Metropolitan Museum of Art in New York, and of which countless reproductions have been made. The 1850 version was destroyed during a British bombing raid on Bremen in 1942. The painting is very large, measuring some 149 by 255 inches (12 by 21 feet, or 378m by 648 centimetres).

The painting depicts an event during the American War of Independence when, on the night of 25th/26th December 1776, General George Washington took an army eastwards across the Delaware River in order to launch a surprise attack on the town of Trenton, New Jersey, which was garrisoned by a force of 1,500 troops from Germany (the “Hessians”) who were fighting alongside the British.

Crossing the river should not, in itself, have been an especially notable event, as the Delaware was not particularly wide at this location and armies had crossed it fairly regularly during the course of the war to this point. Washington had in fact crossed the river the other way a few months previously. However, conditions were not good on this particular night as the weather was poor and a strong wind was blowing. The main problem was the ice that stuck to the boats and had to be hacked off as they crossed. These factors made the crossing both dangerous and daring.

The significance of the event was that it marked a turning point in the war in that the overwhelming victory that followed the crossing had been preceded by a series of defeats and reverses. Morale had been falling among the Americans but news of Washington’s victory at Trenton changed all that.

Leutze’s painting, created 74 years after the crossing, was therefore intended to symbolize the spirit of victory as well as to portray Washington as a hero. It was never intended to be an accurate depiction of an event that happened 40 years before the artist was born and on a river thousands of miles from where he was living. Indeed, the river has more in common with the Rhine in Germany than the Delaware in the United States.

In the painting, Washington is shown standing on a boat that is being propelled across the river by poles and oars. The river is choked by blocks of jagged ice that his companions are clearing a way through. Behind Washington the Stars and Stripes are held proudly by another officer (who is thought to represent James Monroe who was to be the fifth US President). Other boats can be seen in which men and horses are following Washington’s boat.

Everything in this painting points to the heroism of George Washington, with all sorts of devices used to drive the point home. The light of the low sun, veiled by a stormy sky, forms a bright halo for Washington and the flag. The lines formed by the poles and oars, the flag and Washington’s figure all slope in the same direction to stress that progress and victory are inevitable. Despite the obstacles, the courage of the people on the boat will prevail.

As has often been pointed out, there are many errors and anachronisms in “Washington Crossing the Delaware”. The river is wrong (too wide), as is the boat (wrong type), and so is the flag (not in use at the time). Washington would not have been standing up proudly under the circumstances, and he would not have been in the leading boat. The crossing was at night. Indeed, there is very little about this painting that can be taken as a true portrayal of the event in question, apart from the fact that it did actually take place.

The painting’s symbolic importance

However, none of this really matters, because what Leutze was doing was offering an allegory rather than a depiction of a real event. At the time of the painting’s creation the United States was expanding to the Pacific, by means of its victory in the Mexican Wars, and thousands of settlers were moving west to colonize new lands.

Leutze was therefore celebrating this new venture by idealising a much older one. On board the boat with Washington can be seen a cross-section of people who represent Americans of the mid-19^th century. They are pioneers, farmers and settlers, rather than soldiers, and there is also a freed black slave among their number. They are led by an iconic hero towards new promised lands.

“Washington Crossing the Delaware” is misunderstood if the viewer believes that he or she is seeing an accurate representation of General George Washington leading an army into battle. However, if they see it as an allegory of a young nation striding forwards towards a prosperous future based on freedom and justice for all, they will be a lot closer to understanding its message. The painting works first and foremost at an emotional level rather than as a historical document.

© John Welford

Trojan asteroids

Although the vast majority of asteroids (minor planets and rocky debris) in the Solar System orbit the Sun in a belt between Mars and Jupiter, there are many that do not. In particular, there are about 6,000 that can be found in the same orbit as Jupiter, either 60 degrees “ahead of ” or “behind” the giant planet.

These areas are known as “Lagrangian points”, their significance being that this is where the gravitational influences of the Sun and Jupiter cancel each other out. The asteroids can therefore have stable orbits.

These have been named “Trojans” because the larger asteroids have been given names derived from the names of warriors in the Homeric Trojan wars. The two groups are either “Greeks” or “Trojans”, but these objects, locked in their orbits as they are, are fated never to meet in combat.

The name Trojan asteroid has been given to objects that are similarly placed in orbits ahead of or behind other major planets. Mars, Uranus and Neptune are all known to have Trojans, and in 2011 one was discovered in Earth’s orbit, this having the somewhat unromantic name of 2010 TK.

© John Welford

Census at Bethlehem, by Pieter Bruegel the Elder

Census at Bethlehem is a painting by Pieter Bruegel the Elder (c.1525-69) that says much more about the Netherlands in the 16^th century than the scene it purports to depict.

The two Pieter Bruegels

There were two famous painters, father and son, with the name Pieter Bruegel, although the younger used the original family spelling of Brueghel which his father had abandoned. The elder Bruegel was the patriarch of a whole dynasty of well-known painters across four generations.

Pieter the Elder was born in the Netherlands (the exact year of his birth is unknown) and he worked as a painter in Antwerp and Brussels. He is often referred to as the “Peasant Bruegel” in recognition of his favoured subject for painting, namely the peasant life of his homeland.

Pieter the Younger (1565-1636) hardly knew his father, who died when the younger Pieter was a young child, but he became devoted to his father’s memory and copied many of Pieter the Elder’s works, as did other members of his workshop. He also painted many works that were original compositions.

Census at Bethlehem

Because of the copying mentioned above, several versions of this painting are known to exist, so the painting can be attributed to either Pieter, depending on whether one is considering the original or a close copy made only a few decades later. The original dates from 1566.

The scene looks to be nothing more than that of a Flemish village in the snow. A crowd has gathered at a tavern in the left foreground, but life seems to be going on as normal elsewhere, with well-wrapped-up peasants going about their business gathering fuel or walking or skating on the ice.

However, in the centre of the foreground is a woman in a blue cloak riding a donkey that is being led by her husband. This is Mary and Joseph making their way to join the throng of people queuing to pay their taxes.

This is therefore an example of something that was quite common in 16^th century Flemish art, namely the introduction of Biblical themes to a contemporary scene. By so doing, the artist hoped to make the Bible message relevant to the painting’s viewers and to make a moral point as well as a spiritual one.

A dig at the Hapsburgs

However, Bruegel has gone one step further in this particular painting. At the time, the Netherlands (which comprised the whole of present-day Belgium and Holland) was governed by the Hapsburg King Philip II of Spain. The Catholic monarch was far from popular in the Protestant-inclined Low Countries, and it would not be many years before the whole region would rise in revolt at Philip’s attempts to convert the people back to Catholicism.

The clue to Bruegel’s political message is on the wall of the tavern that has become the census/tax office. The poster displays a double-headed eagle; this was not only the symbol of ancient Rome but also that of the Hapsburg dynasty. The oppression of ancient Palestine by the Roman Empire is therefore translated into that of the Low Countries by Hapsburg Spain.

Bruegel’s paintings were not intended for public display but would have been bought by members of Antwerp’s intelligentsia. His witty dig at the Hapsburgs would have been appreciated by whoever bought Census at Bethlehem and proudly showed it to his friends and neighbours.

© John Welford