What does our solar system consist of?
What is a Galaxy?
The sun is at the centre of the solar system then There are 8 Planets and the dwarf planets that orbit around the Sun. Natural satellites, the moons that orbit planets, are also part of the solar system.
A galaxy is large group of stars.
How do stars form?
Stars form when:
1. Stars form from clouds of dust and gas called nebula that are pulled together by gravity. The gas is mainly hydrogen. Scientists is call this collapsing gas and dust a **protostar.**.
2. As the dust particles move faster, the temperature rises to millions of degrees Celsius due to more collisions.
If the Temperature of the protostar is high enough then hydrogen nuclei join together to form helium. This is called nuclear fusion.
3. The forces are balanced and a main sequence star is formed which can remain like this for billions of years.
What are the two opposing forces within a star?
There are two opposing forces acting within the star:
- The force of gravity acts inwards and tends to make the star collapse.
- The energy from nuclear fusion creates a force acting outwards. This force tends to make the star expand.
The force of gravity and force due to fusion energy makes them balanced(Equilibrium)
What is the Lifecycle for a star the same size as the sun?
Nebula and protostar then:
- At this point the nuclear fusion has turned it in to a star. Fusion releases large amounts of energy. At this point we have a main sequence star and they can stay in this form for a long time.
- But at some point the hydrogen begins to run out and the forces become imbalanced so the star collapses inwards(due to gravity) which increases temperature.
- Now helium fuse together to create heavier elements and the star expands become a red Giant.
- But when the star stops fusing helium the star shrinks and forms a white dwarf but because the white dwarf is not fusing helium it becomes cooler and eventaully becomes a black dwarf.
What is the lifecycle for a star bigger than the sun?
- Once these stars run out of hydrogen they leave the main sequence stage then expand into red super giants.
- Once again helium nuclei fuse to make heavier elements.
- At some point, the Red giant stops fusing nuclei and explodes(SUPERNOVA) in which elements heavier than iron are made(due to high temperature) and distributed across the universe.
- After the supernova either one of two objects are formed:
- Neutron star - consists of neutrons densely packed together
- Black hole - Has such a large gravity that not even light can escape
- Stars that are larger than the Sun have much shorter lifespans - in the region of hundreds of millions of years (instead of billions)
- This is because they burn through the fuel in nuclear fusion much quicker than smaller stars
What are the 3 types of satellites?
Gravity provides the force that allows planets and satellites (both natural and artificial) to maintain their circular orbits.
- The moon is a natural satellite. The force of gravity holds the moon in orbit
- Artificial Satellites are man-made
- Geostationary satellites orbit once every 24 hours. They always point to the same part of the earth but orbit less frequently than Artificial satellites.
How does the force of gravity lead to changing velocity but unchanged speed?
- force of gravity causes the satellite to accelerate towards the Earth
- the acceleration causes a change in direction
- velocity changes because direction changes
When an object moves in a circle at a constant speed, its direction constantly changes.
A change in direction causes a change in velocity. This is because velocity is a vector quantity – it has an associated direction as well as a magnitude.
A change in velocity results in acceleration, so an object moving in a circle is accelerating even though its speed may be constant.
What happens if the speed of satellite increases
If the satellite is moving too quickly then the gravitational attraction between the Earth and the satellite is too weak to keep it in stable orbit.
If this is the case, the satellite will move off into space increasing the radius. The satellite needs a greater force of gravity to prevent it from flying off in space.
By moving closer to the earth the gravitational force on the satellite is greater and the satellite remains in stable orbit.
What is red shift?
Red-Shift - observed increase in Wavelength of light from distant galaxies so frequency decreases. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. This effect is called red-shift.
Astronomers have discovered that, in general, the further away a galaxy is, the more red-shifted its light is. This means that the further away the galaxies are, the faster they are moving. This is similar to an explosion, where the bits moving fastest travel furthest from the explosion. Red-shift data provides evidence that the Universe, including space itself, is expanding.
What are all the objects in the solar system?
- The Sun lies at the centre of the Solar System
- The Sun is a star which makes up over 99% of the mass of the solar system
- There are 8 planets and an unknown number of dwarf planets which orbit the Sun
- The gravitational field around planets is strong enough to have pulled in all nearby objects with the exception of natural satellites
- The gravitational field around a dwarf planet is not strong enough to have pulled in nearby objects
- There are 4 rocky planets: Mercury, Venus, Earth and Mars
- There are 4 gas planets: Jupiter, Saturn, Uranus and Neptune
- Some planets have moons which orbit them
- Moons are an example of natural satellites
- Artificial satellites are man-made and can orbit any object in space
- The International Space Station (ISS) orbits the Earth and is an example of an artificial satellite
- Asteroids and comets also orbit the sun
- An asteroid is a small rocky object which orbits the Sun
- The asteroid belt lies between Mars and Jupiter
- Comets are made of dust and ice and orbit the Sun in a different orbit to those of planets
- The ice melts when the comet approaches the Sun and forms the comet’s tail
How does Equilibrium occur in stars?
- Stars are held together by a delicate balance of inwards and outwards forces
- One of these forces is the force of gravity
- This is an attractive force which pulls the outer layers inwards
- The other force is the force of energy
- This is an outward force which is exerted from the expanding hot gases inside the star
How are new elements formed?
The Formation of New Elements
- During the majority of a star’s lifetime, hydrogen nuclei fuse together to form helium nuclei
- As the star runs out of hydrogen, other fusion reactions take place forming the nuclei of other elements
- For example, two helium nuclei (produced by the fusion of 2 hydrogen nuclei) could fuse together to form a beryllium nucleus
Formation of Elements Heavier than Iron
- Elements heavier than iron are produced in supernovae explosions
- A supernova occurs at the end of a massive stars life
- When the star explodes it releases very large amounts of energy and neutrons
- All of the elements which have been produced by the fusion reactio ns get thrown out and combine with the neutrons to form heavier elements
How did we come to the conclusion that the universe is expanding?
- The diagram below shows the light coming to us from a close object, such as the Sun, and the light coming to us from a distant galaxy
The diagram also shows that the light coming to us from distant galaxies is redshifted
- The lines on the spectrum are shifted towards the red end
- This indicates that the galaxies are moving away from us
- If the galaxies are moving away from us it means that the universe is expanding
- The observation of redshift from distant galaxies supports the Big Bang theory
- Another observation from looking at the light spectrums produced from distant galaxies is that the greater the distance to the galaxy, the greater the redshift
- This means that the further away a galaxy, the faster it is moving away from us
What is the big band theory?
The Big Bang Theory
- Around 14 billion years ago, the universe began from a very small region that was extremely hot and dense
- Then there were a series of explosions, which we call the Big Bang
- This caused the universe to expand, cooling as it does so, to form the universe we currently observe
- Each point expands away from the others
- This is seen from galaxies moving away from each other, and the further away they are the faster they move
- As a result of the initial explosions, the universe continues to expand
What evidence is there for the big bang?
Evidence for the Big Bang
- By observing the light spectrums from supernovae in other galaxies there is evidence to suggest that distant galaxies are moving further apart ever faster
- These observations were first made in 1998
- The light spectrums show that light from distant galaxies is redshifted, which is evidence that the universe is expanding – the galaxies are moving away from us - and, indeed, each other
- This is what happens in an explosion
- Matter is first densely packed and as it explodes it, it moves out in all directions getting further and further from the source of the explosion
- Some matter will be lighter and travel at a greater speed, further from the source of the explosion
- Some matter will be heavier and travel at a slower speed, closer to the source of the explosion
What is dark energy and matter?
Dark Energy & Dark Matter
- Over the past two or three decades, astronomers have gathered plenty of evidence helping us to understand the universe much better
- However, there are still many observations that are still not understood, including:
- Evidence from the rotation and motion of galaxies suggests that there is much more matter in the Universe than we are able to account for
- This unseen matter is given the name dark matter and its nature is not currently known
- Measurements of the expansion of the Universe using supernovae suggest that the Universe is starting to expand at a faster rate
- It has been suggested that this accelerated motion is caused by dark energy pushing everything in the Universe apart
- If gravity is present everywhere in the Universe, it might be expected that everything will one day become closer together, but that is the opposite of what we see
- This is another reason why dark energy is a possible solution which could be counteracting gravity and expanding the Universe instead
What do fusion reaction lead to?
Fusion reactions lead to an equilibrium between the gravitational collapse of a star and the expansion of a star due to fusion energy.
