THE COSMIC ENGINEOUR SUN IS JUST ONE STAR IN THE GALAXY AND OUR GALAXY IS JUST

ONE IN THE UNIVERSE

1.1: OUTLINE THE HISTORICAL DEVELOPMENT OF MODELS OF THE UNIVERSE FROM THE TIME OF ARISTOTLE TO THE TIME OF NEWTON

Aristotle’s: model of the universe said the earth was round. However his model of geocentric, meaning he thought that the earth was the centre of the universe. He also believed that the sun and the stars were in a celestial sphere that rotated around the earth

Aristarchus’s: model was heliocentric, meaning that the sun was the centre of the Universe. Aristarchus also believed that the sun was much bigger than the earth and that the reason why everything appeared to rotate around the earth was because earth rotates on its axis once a day.

Copernicus: also brought forward a heliocentric model.

Brahe’s: model of the universe was part geocentric and part heliocentric. He had the planets and stars rotating around the sun. However he had the sun rotating around earth.

Kepler: discovered 3 Laws:1. Planets travel in elliptical orbits around the sun with

the sun at one of the two foci.

2. The speed of the orbiting planet increases as its radius decreases, and the speed decreases as the radius increases.

3. Law of Period: The time a planet takes to orbit is dependent of the radius of the orbit.

Galileo: was the first person to look at the stars and planets with a telescope. He made many observations of planets, stars and moons.

Newton: deduced the Law of Universal Gravitation. Gravity is a force that pulls masses together. Every mass in the Universe exerts a force of gravity on every other mass. The force of gravity between two bodies is determined by their masses and the distance between them.

THE FIRST MINUTES OF THE UNIVERSE RELEASED ENERGY WHICH CHANGED TO MATTER, FORMING STARS AND GALAXIES

2.1: OUTLINE THE DISCOVERY OF THE EXPANSION OF THE UNIVERSE BY HUBBLE, FOLLOWING ITS EARLIER PREDICTION BY FRIEDMANN

Friedmann mathematically proved that the universe was expanding, but he made some assumptions in order to prove it.

He used Einstein’s equations to determine his own solutions about the universe and when he omitted Einstein’s cosmological constant from his equations then all his solutions suggested that the universe was expanding.

Hubble using the world’s largest telescope discovered the cosmological red shift. When light from distant stars and galaxies is examined with a spectroscope and compared to light from the same elements on Earth, the spectrum from the star or galaxy shows a shift towards the red end of the spectrum.

A red shift corresponds to a shift to the lower frequency (longer wavelength). This indicates that the light source, the galaxy is moving away from us. All galaxies show this effect indicating that the universe is expanding. The stretching of space causes the cosmological red shift.

2.2: DESCRIBE THE TRANSFORMATION OF RADIATION INTO MATTER WHICH FOLLOWED THE BIG BAND

About 300,000 years after the Big Bang, the temperature of the Universe had dropped enough for Hydrogen atoms to form from electrons and protons.

From this time the radiation was set free from matter.

At the beginning of the big bang, there was only radiation. However over time ranging from 300 seconds to 1 million years, the particles combined to form atoms (matter).

Radiation tends to interact with charged particles, being bounced around so that it is not free to move through the universe.

2.3: IDENTIFY THAT EINSTEIN DESCRIBED THE EQUIVALENCE OF ENERGY AND MASS

In 1915 Einstein proposed his Special Theory of Relativity in which he deduced the relationship between energy and mass as e=mc2

This equation indicates that energy and mass are simply different forms of the same entity; mass could be created from energy and energy could be created by mass.

2.4: OUTLINE HOW THE ACCRETION OF GALAXIES AND STARS OCCURRED THROUGH:O EXPANSION AND COOLING OF THE UNIVERSE

O SUBSEQUENT LOSS OF PARTICLE KINETIC ENERGY

O GRAVITATIONAL ATTRACTION BETWEEN PARTICLES

O LUMPINESS OF THE GAS CLOUD THAT THEN ALLOWS GRAVITATIONAL COLLAPSE

Expansion and cooling of the Universe

As the universe expanded, it cooled (because the energy has to be distributed over a larger volume). The Steady State theory says that as the universe is expanding, more matter is created to keep its density constant, however, this theory is not supported.

About 10,000 year after the big bang, the expansion of the Universe resulted in the temperature falling enough so that ‘matter’ particles exceeded the light and other radiation that had dominated earlier

Subsequent loss of particle kinetic energy

The temperature of a body is related to the kinetic energy in it particles. So as the particle kinetic energy got lower the temperature decreased. This resulted in the amount of matter in the universe exceeding the amount of radiation.

Gravitational attraction between particles

The Law of Gravitation states that every mass in the universe is attracted by gravity to every other mass in the universe. So stars slowly attracted other stars, which over time resulted in masses of stars clumped together, known as galaxies.

This loss in Kinetic energy meant that the increased gravitational force between particles took effect.

Lumpiness of the gas cloud that then allows gravitational collapse

Lumpiness of gas cloud is where some parts are denser than others.

The small variations in the density of the particles would consequently grow; leading to accretion until eventually our current universe was created

2.4: DESCRIBE THE PROBABLE ORIGINS OF THE UNIVERSE

After Hubble showed in the 1920s that the Universe was not static but expanding then various scientists tried to explain this observation. The two best-known explanations were the Steady State Theory and the Big Bang Theory.

The Belgian, Georges Lemaitre, put forward the Big Bang Theory, in 1927 when he proposed that the Universe began from a primeval atom. For some reason the “primeval fireball” began to expand and as it expanded matter thinned out, cooled down and gradually condensed into stars and galaxies. In 1948 the British astronomers Hermann Bondi, Thomas Gold and Fred Hoyle put forward an opposing theory, namely the Steady State Theory. This suggests that the Universe has always existed essentially the same as it is today. As the Universe expanded a new atom of hydrogen would suddenly pop into existence in the space between galaxies.

Modern astronomers have largely rejected the steady state theory. While the amount of matter being created would be small (less than an atom per cubic metre per million years) it seemed to contravene the principle of conservation of energy and mass. As telescopes improved, astronomers were able to see further and further into the Universe. With the discovery of Quasars at great distances it was found that the Universe was far from uniform. Also, because of the time it takes the light from quasars to reach us, we are actually seeing what the Universe was like billions of years ago. It appears that a lot more quasars existed in the past than are present today.

In 1950, George Gamow predicted that radiation left over from the Big Bang should still be present in the Universe. Just as the spectra of stars are red shifted because they are moving away from us, so too the energy left over from the Big Bang should still be present in the Universe but at a much longer wavelength than it had originally because of the expanding universe. Calculations suggested that the temperature of the Universe should be in the order of 3 kelvin as characterised by a blackbody spectrum with a peak wavelength of around 1 mm. Arnio Penzias and Robert Wilson confirmed this in 1965 when they discovered this radiation now called the background microwave radiation. Its intensity is isotropic (the same in all directions) and its wavelength is consistent with the predicted temperature of just under 3 kelvin.

STARS HAVE AN LIMITED LIFE SPAN AND MAY EXPLODE TO FORM SUPERNOVAS

3.1: DEFINE THE RELATIONSHIP BETWEEN THE TEMPERATURE OF A BODY AND THE DOMINANT WAVELENGTH OF THE RADIATION EMITTED FROM THAT BODY

As the temperature increases the wavelengths become longer.

Hot: more energy is being emitted: short wavelengths.

Cold: less energy is being emitted: long wavelengths.

As the temperature of a body increases the peak wavelength decreases.

3.2: IDENTIFY THAT THE SURFACE TEMPERATURE OF A STAR IS RELATED TO ITS COLOUR

A cooler star, with a surface temperature of 3000-4000 Kelvin’s produces most of its visible radiation at the longer wavelength, or red side of the spectrum, hence appearing red.

As the temperature increases to around 6000 Kelvin’s. The wavelengths peak in the tallow and a star will appear yellow.

At slightly higher temperatures, around 7000 Kelvin’s, the distribution of the radiation is more even and as a result, the star will appear white.

A hotter star, with a surface temperature of 8000 Kelvin’s or more produces most of its visible radiation at the shorter wavelength, or blue end of the spectrum, hence the star appears blue.

Coolest: Dull red Orange Yellow

Hotter: White Blue-White

The hotter that the star is the shorter the wavelength indicating that the hotter the star the increased shift towards the blue end of the spectrum.

3.3: DESCRIBE A HERTZSPRUNG-RUSSELL DIAGRAM AS THE GRAPH OF A STAR’S LUMINOSITY AGAINST ITS COLOUR OR SURFACE TEMPERATURE

The Hertzsprung-Russell diagram plots a stars surface temperature against its luminosity. Each dot is a star. The stars can be classed into groups depending on their position on the H-R diagram. A stars life cycle can also be drawn on the H-R diagram.

3.4: IDENTIFY ENERGY SOURCES CHARACTERISTIC OF EACH STAR GROUP, INCLUDING MAIN SEQUENCE, RED GIANTS AND WHITE DWARFS.

Main sequence: is a diagonal band from the upper left of an hr diagram to the lower right corner of the diagram. Most stars are in this group.

Red giants: is the group of stars in the upper right corner. These are cool giant stars.

White dwarfs: is the group close to the lower left corner of the Hr diagram. These are exceptional small, hot stars.

THE SUN IS A TYPICAL STAR, EMITTING ELECTROMAGNETIC RADIATION AND PARTICLES THAT INFLUENCE THE EARTH

4.1: IDENTIFY THAT ENERGY MAY BE RELEASED FROM THE NUCLEI OF ATOMS

The nuclei of many atoms are unstable.

They try to achieve stability by releasing energy.

They do this in the form of alpha particles, beta particles and gamma rays.

Energy can also be released in the form of nuclear fusion reactions.

In the proton-proton chain, most of the energy is released in the form of the kinetic energy of the products of the reaction. These include Alpha and beta particles and gamma rays.

This is the nuclear binding energy, and may be released in two ways:

o (a) fusion from the combination of light elements into heavier ones (for instance hydrogen into helium);

o (b) fission from the splitting of heavy elements into lighter ones (such asuranium being split into barium and krypton when bombarded by neutrons)

4.2: DESCRIBE THE NATURE OF EMISSIONS FROM THE NUCLEI OF ATOMS AS RADIATION OF ALPHA ALPHA AND BETA PARTICLES AND GAMMA RAYS IN TERMS OF:

–IONIZING POWER

–PENETRATING POWER

–EFFECT OF MAGNETIC FIELD

` –EFFECT OF ELECTRIC FIELD

4.3: IDENTIFY THE NATURE OF EMISSIONS REACHING THE EARTH FROM THE SUN

Emissions from the sun include: Electromagnetic radiation – however most of it is not allowed through

our atmosphere.

Charged Particles – Protons and electrons, this is known as solar wind.|

Neutrinos – very small neutral particles.

The wavelengths of electromagnetic waves emitted by an object are related to the objects temperature.

The sun has a surface temperature of about ~5700K and thus emits primarily in the visible portion of the electromagnetic spectrum in a band from 4 x 10-9 to 4 x 10-9 .

This radiation, along with short wave infrared passes through the Earths atmosphere without being absorbed although some is reflected back into Space by the clouds.

About 7% of the sun’s radiation is below 400nm that is in the Ultra-Violet.

Electromagnetic radiation is visible and invisible.

4.4: DESCRIBE THE PARTICULATE NATURE OF THE SOLAR WIND

Solar wind consists of a stream of ionised particles, mostly protons and electrons that flow from the sun in all directions at speeds of about 400 km.s-1.

The source of the wind is the sun’s hot corona – the outer atmosphere of the sun extending a distance of a few solar radii into space.

Most of the corona consists of vast arches of hot gas – solar flares – that are millions of kilometres in length and are caused by the sun’s magnetic field.

The Solar wind comes from regions called coronal holes, regions of cooler, less dense gas. As the sun rotates there is a periodic variation in Solar wind activity every 27 days.

The Solar wind is responsible for pushing the tail of comets away from the sun.

4.5: OUTLINE THE CYCLIC NATURE OF SUNSPOT ACTIVITY AND ITS IMPACT ON EARTH THROUGH SOLAR WINDS

Sunspot cycle is a pattern of increasing and decreasing sunspots.

Sunsport is a dark spot on the sun with lower temperatures and intense magnetic activity.

Cycle is between 7-13 years.

Two types of emission reaching Earth from the sun: electromagnetic radiation and solar winds.

Earth’s atmosphere and magnetic field shelters as from theses emissions.

The sunspots themselves last for several days although larger ones may last up to a few weeks.

The number of particles and their velocity increases following sunspot activity and solar flares meaning that the solar wind is greater in the time of maximum sunspots.

Sunspot Activity follows an 11 year cycle. They release large amounts of electromagnetic radiation, which affects the earth in way such as:

o Causes aural displays.o Affects earth’s magnetic field.o Overloading electrical power lines, which causes blackoutso Disruption of radio/telephone communication.

4.6: DESCRIBE SUNSPOTS AS REPRESENTING REGIONS OF STRONG MAGNETIC ACTIVITY AND LOWER TEMPERATURE

A sunspot is an area on the sun that has strong magnetic activity and a lower temperature. They appear as dark regions, with an irregular shape.

Sunspots are relatively cool areas (~4500K), with magnetic field strengths some thousands of times stronger than the Earth’s magnetic field, that appear as dark imperfections in the photosphere.

They result from the penetration of magnetic field lines through the photosphere and are ~8000km across. Except for the smaller ones, all sunspots have a dark inner region – the umbra – where the magnetic field is strongest surrounded by a less dark region – the penumbra – where the magnetic field is weakest