Bacchanalian Revel

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Poussin, A Bacchanalian Revel before a Term (1632). Oil on canvas, 98 x 142 cm. National Gallery, London

When it is time to paint a bunch of revelers

Arcadian party goers are drinking and dancing near a pillar.

This pillar has a head on it and they are giving worship to Pan (or possibly Priapus) who were both connected to fertility, partying, dancing and heavy drinking, which is very clear in this painting!

These dancers have been very carefully painted in structured, flowing design; even though they clearly appear to be frantic mad.

Poussin almost certainly researched the landscape from Venetian pictures in Roman collections.


 Edouard Manet, The Balcony (1868). Oil on canvas, 170 x 124 cm. Musee d’Orsay, Paris
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Why the balcony painting was a turning point in Manet’s career
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Disapproval seemed to follow Edouard Manet around Paris. Many critics considered his painting The Balcony discordant when it was exhibited at the 1869 Salon, while some suggested it implied aggression!
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The Battle of San Romano

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Uccello, The Battle of San Romano (1438). Tempura on panel, 182 x 320 cm. National Gallery, London

Who the wonderful Paolo Uccello really was

Florence v Siena in 1432 is the battle depicted in this painting.

Just one part of this battle is shown by Uccello here in London, and the middle figure is Tolentino leading the Florentines on his white horse; he has ‘Knot of Solomon’ up upon his banner!

There are two other versions of this painting: one is in the Louvre in France, and the other in the Uffizi in Italy.

This version in London is very much a linear, rather than painterly, version of the battle and so, so typical of Uccello.

The London panel is probably the left part of the triptych; it probably represents dawn. In Florence, the central part is midday and the one in Paris finishes the set at dusk.

The battle only lasted eight hours in reality, thus the broken lances and the dead soldier are carefully aligned to give perspective in this very old painting.


 Raphael, The Madonna del cardellino (1506). Oil on wood, 107 x 77 cm. Uffizi, Florence
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When ornithology and art history blended together

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Carduelis carduelis is the Latin name for the goldfinch species of bird; this beautiful little creature is often seen in many works of Renaissance art and appears usually in the hands of the child Christ to blend ornithology with art history.

Raphael often united Jesus with John the Baptist when they were children, thus John fittingly became Patron Saint of Florence (according to James Beck, 1993) and anything destined for a Florentine commission meant St John had an almost obligatory inclusion.

Tuscany can be seen in the background of Raphael’s masterpiece where the landscape greatly enhances the beauty of the figures: John’s curls, the plumpness of Jesus and the youthfulness of Mary all add up to make a pure human relationship within this small unit.

Raphael has injected warm flesh tones within an airy landscape of trees, streams and mountains, hence one can almost hear the cascading brook in the Tuscan countryside. The walled city behind, vaguely resembles Florence with the Duomo and Palazzo Signora just about visible in the distance, linking religion to world-centre of art.

Christ appears as a Child and caresses the tiny goldfinch while being protected by the mass of his mother’s body in an arrangement reminiscent of Michelangelo’s Bruge Madonna. Michelangelo’s influence is again evident in the well structured figure of Christ, who somehow doesn’t really look like a child, but is all-knowing, powerful and elegant. He is lifting his arm up to stroke the goldfinch, and tilting his head back in a manner unlike any normal boy.

This is also a painting of two children and one mother. The youngsters are doing childlike things, such as showing a pet to one another with mother looking down protectively, whilst at the same time, Mary is isolated from those children as if to indicate their separate destinies and diverse roles of the future.

Mother Mary, the baby Jesus and the infant St John are all arranged geometrically in Raphael’s painting but the Virgin Mary is at the top of the triangle with the other two figures positioned naturally at her feet.

Despite Raphael own personal style – portraying extreme sweetness of the faces and showing the profound intimacy between the figures – the influence of Leonardo is also evident. There is a realistic reproduction of landscape and a pyramidal composition with Mary at the top, giving the picture stability and balance, thus emulating Leonardo’s most famous work in many ways!

Madonna’s book indicates wisdom and the goldfinch (this beautiful little bird) is symbolic of many things: the soul, resurrection, sacrifice, death, healing and redemption. In this case, the goldfinch probably means suffering and Passion of the Christ.

The glorious goldfinch bird identifies the forthcoming suffering of Jesus because it naturally feeds among the thorns and one particular goldfinch is said to have plucked out a thorn, that was digging painfully into Christ’s brow as he was on his way to be crucified.

Portrait of Leonardo Loredan

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Bellini, Portrait of Leonardo Loredan (1501). Oil on panel, 61 x 45 cm. National Gallery, London

Why the portrait of Leonardo Loredan is so important to art history

Leonardo Loredan was officially the doge of Venice in Italy.

After various conflicts in that hotbed of an area, the Papacy was forced to repay the Loredan family an enormous amount of money in compensation.

This picture is perhaps the very first frontal portrait of a reigning doge, which means that such portraiture back then was usually the profile of the sitter.

The doge here is wearing his ceremonial garments: the hat is called a corno ducale. Venice always had a tradition of formal portraiture for her rulers to be dressed in state robes.

Stylistically, Bellini’s painting is a sculpted portrait – probably inspired by Roman sculpture – thus, Bellini was the most famous portrait artist of the time and made portraiture especially popular.

It is uncertain how this painting made its way to London, though it is thought to have been looted when Napoleon came to Venice.


Manet, Olympia (1863). Oil on canvas, 130 x 190 cm. Musee d’Orsay, Paris
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Who

Energy in Stars

Nuclear_Fusion

Where do stars get their energy from?

The stars in the main sequence have stability as they don’t swell up or shrink.

The Sun also has a  force of gravity exerted on it, meaning it contracts under its own weight. This is balanced by forces directed at the core supporting it against its own weight; that means the Sun doesn’t explode or collapse upon itself, because of what is known as hydrostatic equilibrium.

A bit like a bicycle pump that heats up – gases do the same when compressed – thus, there is a connection between temperature and pressure. Microwave food is similar when you pierce the lid so the pressure / heat is released.

The gas in the middle of a star is being crushed by that above and temperature is proportional to mass, therefore high mass stars have much hotter cores: the weight upon the middle is much higher!

The surface temperature of the star is plotted on the HR Diagram. Because the temperature is found (calculated) by the light emission, it is, at the same time, impossible to see the core, and measure the core’s temperature to a great level of accuracy.

It is the best method for understanding the correlation between how stellar luminosity increases and how energy is released; essentially, how luminosity relates to core temperature which should depend on the star’s mass. Many factors are involved in unravelling the solution to these equations, but the readings are becoming more accurate.

Any light released from a star has escaped – it is believed – a torturous journey. Energy release probably depends on core temperature, and the best estimates can be gained by examining the nature of nuclear reactions that power the star.

Henceforth, the infamous equation E= MC2 relates energy and mass.

When a sugar cube melts in a tea cup it is like mass converting to energy. It realigns power quite quickly. The Sun is similar in that it loses a small amount of mass when using up its fuel in a nuclear explosion in the middle, the same way the mass of the sugar cube reduces but doesn’t vanish and the energy remains but moves.

The Sun will run out of fuel eventually but it will take thousands of billions of years for the mass to convert to energy (and that is a lot of sugar cubes melting!) thus, fire lighters on barbacues burn longer and brighter than matches and eventually run out of mass and energy. This is fuel converting to energy like petrol does in a car. The only difference is that stars have a nuclear reaction to create energy – more like an atomic bomb being dropped.

By splitting the atom a new nuclei of different mass is formed and this is the difference between chemical and nuclear reactions. Energy is the result but in a different way.

Nuclear reactions are the source of the Suns energy and a big bright light is the result!

Nuclear fusion comes in a series of reactions fusing atoms to protons. Then from protons to neutrons. This makes less mass; the missing bit becomes energy, in a conversion process in accordance to Einstein’s equation.

All stars are like the Sun with regard to the power coming from this conversion of mass to energy.

Reactions are like pistons in an engine and are continuous every second, which means – in the case of nuclear reactions – that hydrogen must be present in an abundance to fuel something like the Sun, the same way oxygen would be needed in a a petrol engine but not in such huge volumes!

Hydrogen converting to helium is the fusing process. It creates a chemical reaction known as the proton chain: two hydrogen protons fusing will repel giving an increased force the closer they get; and the higher the temperature, the faster they move, so as to overcome the repulsion. This produces more energy, and lots of it, evident by the illumination like fireworks are full of energy when they light up the sky.

Energy release relates to temperature and luminosity rises with stellar mass. More massive, more hot. Thus, nuclear reactions occur more often at higher temperatures as you would expect.

More energy is released by the nuclear reactions of the more massive stars, hence, the Arches Cluster is in the central region of our galaxy and thought to host one of the most massive stars possible according to the laws of physics, with a mass of over 100M.

The Doppler Effect

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What is the Doppler Effect?

The mass of a star is an astronomical figure. It is measured by using pairs of stars orbiting each other – binary systems!

Pairs in binary star systems are bound together by the force of gravity. The stronger this force is, the faster the pair orbit each other. Oddly enough, stars with bigger masses have stronger gravity force between them and move more quickly.

Using this method, astronomers were also able to prove the presence of dark matter from the rotation of entire galaxies.

Absorption lines in spectra (or the opposite which is emission lines) and other such narrow features must be detected from both the stars (in the binary pair) to measure their speeds using the Doppler Effect.

The orientation is also very important because viewing from above or below the orbit you wouldn’t get any doppler effect. They would appear side by side, still moving around, but never out of sight.

When aligned to the orbit properly, you will see the stars move cyclically toward and away, again and again. They eclipse, and this is the Doppler Effect like a police siren getting louder and quieter, and then louder and quieter.

It is then possible to get accurate measurements of the star’s mass. Eclipsing stars pass in-front and behind each other and therefore changes in the brightness or luminosity occur; like for instance, when we see solar eclipses here on Earth and it can get very dark for a moment during the day!

You can calculate orbital speed from these movements and measure mass as from that, however, estimating mass when the stars do not eclipse is very difficult.

A smaller Doppler Effect reading means, smaller (slower) speed and more inaccurate estimation. The stars in the main sequence are evolutionary (meaning they get hotter and brighter moving through their lifecycle) and not of the same mass.

The HR Diagram is very useful for separating stars via temperature, luminosity, brightness and mass; and as such, all of these factors are hugely relevant for a great many things in astronomy, serving as a pre-requisite all kinds of research.

Mass is directly related to luminosity which is related to temperature and this is a reflection of the structure and process powering the star and generating the energy of the star, thus all of these factors are interrelated.

Stars must have a power source like the nuclear reactions in the middle of the Sun to power them, or they would cool and fade away. Using the HR Diagram the bigger the star, the higher the luminosity and the greater the energy production – this is clear.

The more massive the star, the more fuel that is being burned, and the energy produced equals brightness and (even greater) luminosity.

Brightness is dependent largely upon size; so for instance, a star that is 10 times the size of our Sun is 10,000 times brighter!

With luminosity being proportional to size it is possible to figure out how long stars live. Bright stars are burning more quickly and this means they have a shorter lifespan. There are far more faint stars than luminous ones on the HR Diagram for this reason – the bright ones aren’t there for much longer!

The HR Diagram

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Who it was that was responsible for the HR Diagram 

Clusters and constellations are different.

Constellations are not physically connected, but are patterns in the night-sky. Clusters however, are held together, and clusters are relatively close groups of stars, held by by their gravitational force!

This is hugely convenient for the study of stars. Clusters form together from the same material and this means that if differences are detected by astronomers, these differences are a result of change; thus, processes during the life cycle of the star are caused by a change and help build the jigsaw puzzle.

Within any cluster – it is pretty obvious – the collection of stars will all be approximately the same distance from us here on Earth.

Any difference in brightness or luminosity, in the cluster, is therefore not going to be related to distance. It is down to the energy within the star itself; and this is crucial for astronomy with regard to the life cycle of stars, and the physical processes that motor them.

The Jewel Box is a fine example. It is well known for the difference in brightness and range of colour; hence the name. It is now well known that the variety of colours in a cluster like The Jewel Box implies a difference in temperature.

The fact that the stars in the Jewel Box differ in appearance is important when you think they were formed at approximately the same time. Patterns and spectra conveniently provide relevant information on temperature and chemical composition.

The distance measurement is still very important though. This has been very accurately detected with scopes for a long time and can be used to calculate luminosity / light radiation as well, by factoring in how much light is actually received here on Earth alongside the distance which is far more certain.

There are enough variables to play with to gather enough accurate information, despite the vast distances involved!

The diagram by Hertz and Russell (HR Diagram) shows how stars have been allowed by nature just certain combinations of temperature and luminosity; there are limits involved with a range of luminosity or temperature a star has.

The formation of very luminous stars and very faint stars can conveniently be mapped by the laws of physics, thus there are very clear features on the HR Diagram, above.

Thick strip = highly luminous star of great temperature in the top-left. Faint cool stars are bottom right.

Luminosity is at its greatest with a bright blue color, before becoming red and fainter; above the Main Sequence are the red giants cooler than the Sun, with an orangy tint of visible light emission.

In the upper regions we have the super-giants, and these cover a wide range of temperatures.

The Sun is the benchmark for luminosity, and we therefore measure luminosity in general as a proportion of the Sun’s luminosity.

Toward the bottom of the HR Diagram there is a group of faint but hot stars known as white-dwarfs; they are in fact invisible to the naked eye.

Certain stars occupy certain regions of the HR Diagram. They move around this diagram because they don’t stay constant – clearly – but change in size and temperature during their lives / life-cycle.

Most stars appear in the main sequence.

Very long periods of time understandably involve tiny changes; thus, death stars are the ones that live for a fixed period.

Stars emit huge amounts of radiation continuously. Like a candle burning brightly, the stars only have a finite supply of fuel, which means the properties change as the fuel dwindles and the star moves further away from the main sequence.

Certain stars like super giants and white dwarfs don’t appear in young clusters, but do in older ones. This suggests their properties change, thus evolve in a life cycle rather than being born like it.

In the main sequence there are more cool / faint stars, and fewer luminous ones.

Logarithms are often used in astronomy because of the huge mathematical calculations, thus the magnitude scale represents brightness of stars and galaxies. Hence, our eyes respond to the brightness changes in a logarithmic way.

This isn’t enough to explain why stars cannot be found in every region of the HR Diagram though!

The Structure and Life of Stars

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Why stars have a life quite different

We can learn about the Universe from the production of heavier elements found here on Earth.

It is the structure and the life cycle of stars that played a crucial role in the chemical composition of the Universe and how it has changed over time – something called nucleosynthesis – and this physical process is just one part of a chain of events in the evolution.

The Sun is our star. It had a birth and will one day have a death!

At 150 million km from Earth, the Sun is 270 000 times as near us, than the next closest star, which of course is Alpha Centauri.

By studying the surface of our Sun, astronomers can infer the behavior of its interior; thus, it’s atmosphere includes: the photo-sphere, the chromosphere and the corona.

Dynamic and variable is the brightness and activity of the Sun, meaning it must contain a power and energy source. The problem surrounding what fuels the Sun had baffled many scientists until nuclear reactions were discovered about a hundred years ago.

Nuclear reactions are very different to normal energy provided by gas or coal or oil for instance; nuclear reactions need no oxygen; nuclear reactions generate heat and light for a far smaller amount of fuel.

These hydrogen nuclear reactions – it is now estimated – will sustain the Sun for another ten-thousand, million years and the Sun is just half way through its hydrogen fuelled part of the life cycle!

Astronomers deduce what is known about the Universe by observation from very great distances, thus analyzing the radiation received and similar experiments can be conducted in laboratories back here on Earth as well.

Nuclear reactions in space do have similarities to those providing energy here on Earth: nuclear power stations for electricity and nuclear bombs for destruction are two examples.

Scientists have now modeled what the Sun is like deep inside. It is mostly made up of hydrogen gas right the way through; thus, the hydrogen has to be at an extremely high temperature, for the nuclear reactions to take place. This means the reactions take place right in the middle, where of course it is hottest!

Energy radiates away from the core, it is absorbed and re-emitted continuously, while travelling through the radiative zone. Thus, high energy photons known as gamma rays are released during this process, and photons are then transferred to the surface of the Sun by the convection process.

Radiation and convection are similar concepts, because they transfer energy from a hot to a cool region. With radiation though, no matter actually moves, thus the energy is transferred, and energy is transferred by protons.

Convection is different.

Convected material moves along with the heat energy carried with it. This cannot happen with solids, thus a layer of hot gas or liquid, lays beneath a layer of cooler gas or liquid. Cooler material will sink under the hot layer (like hot air rising) and the two will separate!

These events repeat themselves and material constantly rises and heats, then cools and sinks. Temperature slowly increases toward the center (as we already know) and density does too, making the conditions perfect for nuclear reactions to occur. And they do!

Like when water boils, the heat transfers up with bubbles that get stronger; rising columns of hot matter do the same in the convective zone near the Sun’s photosphere.

Astronomers use helioseismology and the physical process that powers the Sun to understand how it functions. It was only in the 1960s that scientists realised that the surface of the Sun is constantly moving; there are regions contracting and expanding all of the time.

These vibrations and oscilllations affect the whole Sun. Temperature and density affect the Sun’s vibrations like a drum muffled by a cushion; thus, sound waves are affected by all of this activity as you can imagine.

Using sound wavelength activity, it has become possible to determine the inner structure of the Sun; like geologists understand the inner structure of the Earth, using the sound vibrations caused by earthquakes tearing up the Earth’s crust.