What is the Solar System?
The solar system consists of a star (the sun) with things orbitting it...
- there are 8 planets which orbit the sun in circular patterns called ellipses
- the inner planets are those closest to the sun (Mercury, Venus, Earth and Mars)
- the outer planets are Jupiter, Saturn, Uranus and Neptune
- There are other things within the solar system such as dwarf planets, comets etc. which all orbit the sun aswell; in addition, planets have moons orbitting them.
How old is the Solar Sytem, and how did it form?
- The solar system was formed when large clouds of ash and dust were squeezed slightly
- Once the particles had moved a bit closer to eachother, gravity took over and the whole cloud collapsed in on itself.
- The particles at the centre of the collapse formed a prostar, (the temperature got high enough for fusion to take place where hydrogen nuclei join together to make helium)
- This process gives out a lot of heat and light and this created a star (the sun)
- Around the sun, material from the cloud containing helium, hydrogen and heavier elements clumped together becoming planets
- The oldest rocks on earth are meteorites, we believe formed shortly after the birth of the solar system. These rocks are 4500 million years old, making the solar sytem at least this old.
Asteroids and Comets:
- Asteroids and comets are made from all the materials left over after the formation of the solar system
- The rocks between Mars and Jupiter didn't form a planet but stayed as small lumps of, these are asteroids.
- Comets are balls of rock, dust and ice which orbit the sun in elongated ellipses, often in different planes from planets.
- As a comet approaches the sun, it's ice melts which leaves a a bright tail of gas and debrees, this is what we see from earth.
What's beyond the solar system?
- Our sun is one of thousands of millions stars which form the Milky way galaxy
- The whole universe has more than a thousand million galaxies...
- Galaxies are often millions of times further apart than the stars are within a galaxy
- This means that a lot of the universe is empty space
How are distances measured in space?
- Outside of the solar system, the distances between stars and between galaxies are so enourmous that kilometers aren't an appropriate measurement.
- So instead lightyears are used, a light year is the distance that light travels through a vacuum in one year
- Light travels very fast, 300,000km/s
- REMEMBER: a light year is a measure of distance, not time.
Important sizes and ages:
- Diameter of the Earth
- Diameter of the sun
- Diameter of the Earth's orbit
- Diameter of the solar system
- distance from the sun to nearest star
- diameter of the milkyway
- distance from milkyway to the nearest galaxy
- Earth- 5000 millions years old
- Sun- 5000 millions years old
- Universe- 14000 millions years old
What can radiation tell us?
- We can learn about a star by studying the electromagnetic radiation it emits. For example, the colour the star appears can tell us its surface temperature
- You can also work out how far away a star is, for nearby stars you can use parallax (this is when something appears to move when you look at it from distant places). Astrononmers take pictures of the sky six months apart, which is when earth is at oppostie ends of its orbit.
- The movement of a star between the two photos lets you work out how far a way it is, as stars further away appear to move less and really distant star don't move at all.
- Another way to measure it's distance from earth is to measure a star's brightness
- However, a star that looks very bright on earth could be close but not that bright, or a very far away and very bright
Atmosphere and Light Pollution:
- If you're trying to detect light, the atmosphere can cause problems as it absorbs of the light from space before it reaches us
- In addition, light pollution such as the light going upwards from streetlamps, can make it hard to see dim objects.
Why do we see galaxies and stars as they were?
1. Electromagnetic radiation travels very fast meaning it can travel around the earth in 0.13 seconds.
2. The sun is about 150 million km away from earth, meaning the radiation from the sun that reaches us must have left about 8 minutes before we actually see it.
3. This means we see the sun as it was 8 minutes ago
4. Since the nearest star to us is 4.2 light years away, light from it takes 4.2 years to reach us meaning we only see the star as it was 4.2 years ago.
5. The further away something is, the longer it takes for the light it emits to reach us, meaning we see it as it was longer ago.
Red Shift and The Big Bang Theory:
- As a galaxy is moving away from us, the wavelength of it changes and the light becomes redder, this is known as red shift.
- By seeing how much of the light has become red you an work out how quickly it is moving away. The greater the red shift the faster it is moving away.
- Observations have told scientists, the more distant the galaxy, the faster is moves away from us.
- This provides evidence that the whole universe is expanding.
- It has proven (with red shift) that the galaxies are moving apart from a single point but people question how this began
- According to the big bang theory, all the matter and energy in the universe must have been compressed into a very small space and then exploded, which caused the expansion of the universe
- The current rate of expansion csn be used to estimate the age of the universe, it is believed the Big Bang happened about 14 thousand million years ago.
The Changing Earth:
Rocks provide a record of changes in the earth:
- Erosion occurs everywhere for example cliffs are worn away by the sea
- However, something must be making new rock- an example of this is when a volcano errupts the lava sets forming new rock
- Fossils also provide evidence that rock is always forming, animals and plants are found in the middle of rocks meaning the rocks must have built up around them
- The age of the earth can be estimated using rocks- the oldest rocks found so far are about 4,000 million years old.
Rocks are constantly being recycled:
- Particles eroded from existing rock get washed into the sea and become sediment, these build up into sedimentary rocks.
- These can get pushed to the surface or can descend into the heat and pressure inside the earth . If the rock descends the structure can change, sometimes because the rock melts and cools
Before the theory...
- For years the same fossils were found on oppostie sides of the atlantic ocean and many people believed this was becasue of 'land bridges' which had now sunk or were underwater.
- There were other unanswered questions aswell- such as why the african and south american coastlines matched so well and why the fossils of sea creatures were found on mountains
- He believed that it was possible that Africa and South america were previously one continent which had split, and when he looked for evidence he found it.
- There were matching layers of rock on both continents aswell as similar fossils
- His theory of continental drift, stated that about 300 million years ago there was a supercontinent called Pangea, but parts of it broke off because the continents were slowly drifting apart.
Why wasn't Continental Drift accepted at first?
- His theroy of 'drifting' wasn't detectable and many believed it was simply impossible
- In addition Wegner was a meteorologist which many thought meant he wasn't qualified to make this sort of prediction
Why was the theory eventually accepted?
- In the 1950's scientists investigated the Mid-Atlantic Ridge and found evidence that magma was rising up throught the sea floor and solidifying. This suggested the sea floor was spreading by a few cm each year.
- In additon, it was discovered that as the liquid magma was rising the iron particles were aligning with the earth's magnetic field at the time. This meant that because the earth's magnetic field swaps polarity every half a million years, there were strips of rock in a 'zebra pattern' with alternate polarities.
The Structure of the Earth:
- The earth has a crust which is very thin, only around 20 km thick. The crust is made up of oceanic crust and continental crust
- Below that is the Mantle, this is liquid but flows very slowly and has many properties of a solid. This flows in convection currents because of the heat from the core.
- At the centre of the earth is the core, we believe this is mainly made from iron and nickel.
- Tectonic plates are large peices of the crust which float on the mantle
- The convection currents, caused by the heating of the mantle by the core, casue the plates the move arounf
- Tectionic plates will occasionally jolt suddenly which can cause an earthquake
- Volcanoes often form at the boundaries of two plates, where they meet. Magma is produced which can rise up forming volcanoes
- As two plates crash into eachother, mountaines are formed. (the himalayas are found where the Indian and Eurasian plates collide).
- When there's an earthquake, it produces shock waves which travel on the surface and inside the earth. We can measure these waves using seismographs.
- Seismologists measure the time it takes for the shock waves to reach each seismograph
- They also note which parts of the earth don't recieve any shock waves.
- There are two different types of seismic waves, P-waves and S-waves.
P-waves: These travel through solids and liquids, they also travel faster than s-waves and are longitudinal
S-waves: These only travel through solids, are slower than p-waves and are transverse.
- When seismic waves reach a boundary between different layers of the earth some waves will be reflected
- The waves change speed as the density changes in the mantle and core, this can cause the waves to change direction and is known as refraction.
- The speed tends to change gradually, resulting in a curve, however if there is a sudden change there will be a kink in the path
What Seismograph results tell us:
- Roughly half way throught the earth, the P-waves change direction suddenly, this indicated there is a abrupt change in properties from the mantle to the core
- S-waves are not detected in the outer core which tells us it it is liquid, s-waves only travel through solids
- P-waves travel faster through the inner core which suggests it is a solid
- S-waves DO travel through the mantle which shows it is a solid, it only melts and forms magma in some areas.
Features of a wave:
- Waves carry and transfer energy in the direction that the wave travels.
- The bigger the amplitude the more enery a wave has
- The wavelength is a full cycle from e.g. crest to crest
- Frequency is the number complete waves passing a certain point each second, measured in hertz Hz. To work out the distance a wave has travelled: distance= speed x time
Most waves are transverse, such as light and s-waves
- In Transverse waves, the vibrations are at 90 degrees to the direction of the wave.
Some waves are lonitudunal, such as sound and p-waves
- In longitudinal waves the vibrations are along the same direction as the wave is travelling.
Wave Speed= Frequency x Wavelength