What is in our solar system?
- The Sun (a star)
● Eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)
● Dwarf planets (Pluto)
● Natural Satellites (Moons)
● The asteroid belt (this exists between Mars and Jupiter)
● Comets are frozen rocks that move around the Sun in often very elliptical orbits
Where is our solar system?
- Milky Way galaxy, a collection of around 100 billion stars.
How was our Sun formed?
- 4.5 billion years ago
- a cloud of gas and dust (a nebula) was pulled together by gravitational attraction.
- particles in the cloud got faster and collided more. The gas warmed up and eventually became hot enough to glow. This was a protostar.
- the protostar gets more dense, more collisions take place and it gets hotter. Eventually the cloud gets hot enough for hydrogen atoms to fuse, forming helium. We call a star in this state a main sequence star.
Why does the Sun remain in the main sequence stage?
- the gravitational attraction still pulling on the gas is balanced by the outward force of the radiation from the nuclear fusion in the core.
- forces are in equilibrium.
Why do we have uranium?
Uranium and other such heavy elements naturally present on Earth can only be formed in a supernova explosion so the Sun must have formed from the remnants of a supernova.
What is going to happen to our Sun eventually?
- When a star starts to run out of hydrogen to fuse, its core collapses and the outer layers swell, cool down and the star will become a red giant.
- Here, helium and other light elements in the core fuse to form heavier elements.
- When there are no more light elements in the core, fusion stops and no more radiation is released.
- The star collapses, becoming a white dwarf
- Such stars eventually fade out becoming black dwarfs.
What would happen eventually if our Sun was much bigger?
- Stars much bigger than ours become red supergiants then they collapse.
- more mass the collapse is more violent and a supernova explosion occurs.
- explosion compresses the core into a neutron star.
- If the original star was massive enough, it becomes a black hole instead of a neutron star.
How do we decide if something is a planet, moon or satellite?
- A planet orbits a star, enough gravity to make it spherical and sweeps out its own orbital path of other smaller objects.
- A moon orbits a planet.
- A satellite is something that orbits something else.
What provides the force that allows planets and satellites (natural and artificial) to maintain their circular orbit?
Gravity. It is an example of a centripetal force because it is acting towards the centre of a circle.
Describe a circular orbit.
- An object orbits another at a constant speed. Its direction is constantly changing so its velocity is changing
- Therefore we say the object is accelerating towards the centre of the circle. The acceleration is a change of velocity per second.
What happens to the orbit of an object if its speed changes?
If an object in orbit slows down, it will fall into a lower orbit, if it gets to slow it will crash to the surface
- If an object in orbit speeds up, it will move to a higher orbit, if to fast it will fly off to space
- At the correct speed an object will orbit at a constant height and speed.
What is red-shift?
Light waves are stretched out if a star or galaxy is moving away from an observer. The wavelength of the light increases.This is called red-shift because the light is shifted towards the longer wavelength - red end of the visible spectrum.
What is red-shift evidence for?
universe is expanding
What does the Big Bang theory suggest?
The universe is expanding and originated as a very small and extremely hot and dense region.
What other evidence is there for the Big Bang theory?
scientists discovered microwaves coming from every direction in space, there must have been a massively
energetic event in one place to still have evidence of it today. This radiation was called the Cosmic Microwave Background Radiation
Were there any other theories for the origin of the universe?
The Steady State theory suggested that the universe was expanding, but it had always been there and matter was created into the spaces that the universe expanded into.
What will happen to our universe?
1)[If the universe is less dense than a certain amount] Expand forever, the stars will gradually die out and the universe will cool (Big Yawn)
2) [If the universe is more dense than a certain amount] Stop expanding and collapse (Big Crunch)
