Space (separate science only)

Question 1

State the 8 planets in order of closest to furthest from the sun

Answer 1

Mercury

Venus

Earth

Mars

Jupiter

Saturn

Neptune

Uranus

Question 2

Explain what the difference between a planet and a dwarf planet is.

Answer 2

To be a planet something must:

1. Be large enough for its gravity to have cleared its own orbit of other debis
2. Be large enough for its gravitational pull to have fomed it into a spherical shape

Dwarf planets are bodies orbiting the sun that have not managed to fulfil one or both of these criteria

Question 3

What are the general differences between the orbit of a planet and the orbit of a dwarf planet?

Answer 3

1. Dwarf planets orbits tend to be more eliptical than a planets (higher eccentricity)
2. Dwarf planets orbits are inclined from the zodiacal plane but the orbits of planets are not.

Question 4

What is an asteriod?

Answer 4

These are small rocky bodies orbiting the sun, mostly between the orbits of Mars and Jupiter

Question 5

State 5 dwarf planets

Answer 5

Pluto

Ceres

Eris

Haumea

Makemake

Question 6

What is a comet?

Where to comets originate?

Answer 6

A comet is a ball of ice and dust that is orbiting the sun in a very eliptical orbit

Short period comets originate in the kuiper belt, long period comets originate in the Oort cloud.

Question 7

What is the life cycle of a star much larger than our sun

Include the elements that are created by the star at each stage

Answer 7

1. A protostar forms within a nebula
2. Fusion ignites in the protostar and it becomes a main sequence star, it remains here for most of its lifetime

Helium is fused to form hydrogen here

3. The core of the star runs out of hydrogen to fuse and gravitational forces now overwhelm the thermodynamic pressure forces and the star collapses inwards. As it collapses it gets hotter and hotter until a layer of the star surrounding the core starts to undergo fusion. The outward pressure force increases and the star swells to become a red supergiant.

This star is hot enough to neuclei together to form all of the elements up to iron

4. The Red supergiant runs out of fuel and collapes in on itself again. When it has collapsed enough to be hot enough to create fusion, the outer core undergoes a massive wave of fusing creating a massive explosion. This is a supernova.

All of the known elements are formed during this stage

5. The inner part of the star then collapses again. If the mass of the core is less than 1.4x the entire mass of our sun it collapses to become an incredibly dense neutron star. If the mass of the core is greater than 1.4x the mass of our sun then the core collapses into a singularity - a black hole

Question 8

Describe the life cycle of a small main sequence star, such as our sun

For each part of the life cycle state the elements created in the star

Answer 8

1. A protostar forms within a nebula
2. Fusion ignites in the protostar and it becomes a main sequence star, it remains here for most of its lifetime

Hydrogen is fused to form helium here

3. The core of the star runs out of hydrogen to fuse and gravitational forces now overwhelm the thermodynamic pressure forces and the star collapses inwards. As it collapses it gets hotter and hotter until a layer of the star surrounding the core starts to undergo fusion. The outward pressure force increases and the star swells to become a red giant.

Hydrogen is fused to form helium

4. the Red giant runs out of fuel and collapes in on itself again. When it has collapsed enough to be hot enough to create fusion, helium is fused into larger elements in one great and brief event that ejects the outer layers of the star to form a planetary nebula

Helium is fused to form heavier elements here

5. The inner part of the star collapses to create a dense hot white dwarf star. This is very dense and no fusion occurs. it gives of light as it cools to become a red dwarf then a brown dwarf

Question 9

What is a main sequence star?

what is the relationship between the mass of the star and how long it remains on the main sequence.

Describe the forces acting in a main sequence star

Answer 9

A main sequence star is a stable star. Stars will remain on the main sequence for the majority of their lifetime. The lower the mass of the star, the more slowly it uses up its fuel so the longer it remains on the main sequence.

Inside a main sequence star, the gravitational force trying to make the star collapse inwards are balanced by the radiation pressure from the fusing hydrogen neuclii which is exerting a force outwards.

Question 10

Describe how stars are formed in a nebula

Answer 10

1. Nebula are large clouds of hydrogen and helium gas, some areas of the nebula are more dense than others.
2. The stronger gravitaitonal force of the more dense areas pulls the surrounding gas in the cloud towards it
3. As the gas falls towards the denser area energy is transferred from the gravitational potential energy store to the kinetic energy store. The gas particles get faster and therefore hotter. This is now an object called a protostar
4. As the protostar collapses in on itself it gets hotter and hotter. When it reaches 15 million kelvin it is hot enough for the hydrogen neucli to form into helium.
5. When fusion ignites the outer layers of the protostar are ejected into orbit around the star, this material will eventually coalesce into planets.

Question 11

Explain why neutron stars appear to give off pulses of radio waves (pulsars)

Answer 11

Neutron stars spin at an incredibly fast rate. As they spin they give off radio waves in beams from the magnetic north and south poles, which are in a different place to the pole around which it spins

This acts like a lighthouse beam, when the beam is pointing directly at us we experience a bright radio beam, then as it passes the radio wave intensity drops off to nothing again.

Question 12

Explain why Neutron stars are incredibly dense

Answer 12

An entire neutron star is made of neutrons tightly packed together. This is means there are no spaces between the subatomic particles, like there are in atroms, so the entire star is as dense as the nucleus of an atom

Question 13

Explain why black holes cannot be seen directly

How do we detect black holes?

Answer 13

Black holes have a strong enough gravitational force that even light cannot escape its gravitational pull. This means that light cannot leave the black hole and get to the Earth, meaning that we cannot see it

As material falls into a black hole it gains energy and gets hotter. As it heats off it gives off light and infrared waves which reach the earth and can be detected

Question 14

What is the Hertzsprung-Russell diagram?

Explain why this diagram is useful

Answer 14

The Hertzsrpung-russel diagram is a chart that plots each star on a scale where its temperature is compared to its brightness.

It can be used to show which stars are on the main sequency and which ones are red giants, red supergiants and white dwarfs. This classification can then be used to predict what will happen to the star in the future and to infer some of its characteristics from similar stars.

Question 15

What is the doppler effect?

Explain why red shift and blue shift occur

Answer 15

The doppler effect is the changing of the wavelength (and therefore colour) of the light emitted by an object when that object is moving towards or away from you.

Red shift is when the light moves towards the red end of the spectrum (the wavelength becomes longer) this happens when the galaxy is moving away from us

Blue shift is when the light oves towards the blue end of the spectrum (wavelength becomes shorter) this happens when a galaxy is moving towards us

Question 16

Explain why the Andromeda galaxy is blue shifted

Answer 16

The andromeda galaxy is blue shifted becuase it is moving towards us. This is becuase the gravitaional force between Andromeda and The Milky Way is pulling the two galaxies towards each other at a rate that overcomes the expansion of the universe

Question 17

What is a galaxy?

Answer 17

A massive collection of billions of stars bound together by gravity and all orbiting a common centre

Question 18

Explain why galaxies moving away from us are red shifted

Answer 18

The galaxy is the sours of the waves. After the galaxy emits a wavefront of light it then moves in the opposite direction to the wave motion before emitting the next wave. This has the effect of lengthening the wavelength of the wave.

Question 19

What is hubble’s law?

Explain how it can be used to find out how far away a galaxy is.

Answer 19

Hubble’s law states that the distance of a galaxy from the earth is proportional to the speed of recession of the galaxy.

v = Hd

v = speed of recession (km/s - kilometers per second)

H = Hubbles constant (km/sMpc)

d = the distance of the galaxy from the earth (Mpc - mega parsec)

To find the distance of a galaxy away from the earth first use the doppler shift to find the recession speed in km/s. Then rearrange the Hubbles law equation to give

d = v/H

Question 20

Describe the motion of most galaxies relative to us

Answer 20

The galaxies are all moving away from us. The only galaxies that are not doing this are ones that are close enough to be affected strongly by the gravitational force of the milky way (e.g. Andromeda)

Question 21

What is the relationship between the distance of a galaxy from us and the amount of red shift it experiences?

Explain why this is

Answer 21

The further away a galaxy is from us, the more red shifted the light that it emits. This is because galaxies that are further away from us are moving faster away than galaxies that are close by

Question 22

Describe the big bang

Answer 22

The big bang is the theory that all of space, time and matter all started off in one place and exploded outwards. It is scientifically accepted as the most likely theory for the origin of the universe.

Question 23

Describe 3 bits of evidence for the big bang

Answer 23

1. Galactic red shifts - the further away a galaxy is the the more ded shifted the light is, meaning that it is travelling faster. This implies that all of the galaxies started in the same place.
2. Cosmic microwave background radiation - During the big bang gamma rays were predicted to be released. As time and space has streched the waves have also stretched, so now the gamma rays are longer microwaves that can be detected coming from all directions at once
3. Proportions of hydrogen (75%) and helium (25%) in the universe - the probotions of hydrogen and helium are the same as in the center of a star. This follows the theory that at the begining of the big bang the entire universe was one large fusing star (big bang nucleosynthesis)

Question 24

Explain why the sun radiates visible light, ultraviolet and infraed radiation

Answer 24

In the core of the sun protons are fused together to create helium nuclei. This process has a mass defect (the mass of the helium is lower than the mass of the hydrogen that created it) and that mass is released as energy in the form of gamma rays.

The gamma rays emitted are transferred into thermal energy in the convetion zone of the sun, the convection zone heats up the phososphere which emits the energy as visible light, infrared and ultraviolet radiation.

Question 25

Describe what happens to the intensity and wavelength of light that a star produces when it enters its giant phase towards the end of its life cycle.

Answer 25

Towards the end of its life cycle a star will swell to form a red giant or a red supergiant. This causes the star to increase in luminosity (become brighter) but release light of a longer wavelength (it becomes more red)

Question 26

Describe the effect of moving from the red giant to the white dwarf phase in terms of wavelength and luminosity

Answer 26

The luminocity of the star goes down, this is becuase no fusion is occuring so the total power output drops by a large ammount The wavelength becomes shorter, this is becuase the light is no longer being emmited from a large cooler star surface with a large area but from a very hot compact core remnant, meaning that there is a higher surface temperature. This occurs becuase the cooler outer shell of the star is blown off as the star transitions from the red giant to the white dwarf phase

Question 27

Why are elements heavier than iron only created by fusion in a supernova (not in the core of a star)

Answer 27

Fusion of elements greater than iron takes in energy rather than releasing it. This means that fusion of these elements cannot be used to power a star. In a supernova there is a large bust of fusion releasing a lot of energy at once. This energy is transferred to thermal energy of atomic nuclei in the sun, causing them to collide with each other and fuse into heavy elements, storing energy inthe nuclear potential energy store as part of this process

Question 28

What type of star is the sun? How long will it remain in this state for?

Answer 28

The sun is a main sequence star of slightly lower than average mass. It will remain in this state as a stable main sequence star for another 5 billion years

Question 29

Compare the orbit of planets and moons

Answer 29

Similarities: Both have eliptical orbits Both rotate as they orbit They are both held in their orbit by gravity Differences: Planets orbit the sun and moons orbit a planet Planets have cleared their orbital path of debris while moons have not (e.g. ring systems)

Question 30

Compare the orbits of moons and artificial satellites

Answer 30

Similarities Both are held in their orbit by gravity Both orbit around a planet Differences Moons have eliptical orbits while satellites tend to have spherical orbits Moons tend to orbit in the plane of rotation of their planet, but artificial satellites often do not The radius of orbit and therefore the period of orbit (time taken for one complete orbit) tends to be longer for moons than for artificial satellites.

Question 31

Descrbe the force required to make something move in a circular motion Explain how this occurs for satellites

Answer 31

To make something move in circular motion there needs to be a force acting at right angles to the direction of motion. As the force is not acting with or against the motion it does not accelerate or decelerate the body, instead it makes it move in a circle In an orbit it is the weight force that holds the body in orbit. If the body is travelling at the right speed at the right distance, the weight force will cause the body to constantly turn towards the earth without falling towards it.

Question 32

Explain why the velocity of a body changing when an object is in orbit but not the speed

Answer 32

When an object is in orbit the centripetal force does not act with or against the motion (it is a right angles) this means it does not speed up or slow down the body so speed does not change. Velocity is a vector, it has both magnitude and direction. When a body is in orbit the force makes it change direction, this causes the velocity to change becuase the direction is changing

Question 33

Describe two factors that cause a body orbiting with a larger radius to have a longer period (time for one complete orbit)

Answer 33

1. The body has further to travel in its orbit 2. It has to travel at a slower speed to remain in orbit becuase the force of gravity is weaker further away from the Earth

Question 34

What are satellites used for?

Answer 34

1. Space telescopes 2. Scientific research - international space station 3. Survalence 4. Global positioning satellite 5. Communications - TV and mobile phone communications 6. Monitoring the weather

Question 35

What is a geostationary satellite? Explain why they need to orbit at a specific radius around the centre of the earth

Answer 35

A geostationary satellite is a satellite that always stays above the same place on the Earth To be geostationary it needs to orbit the earth with the same period that the earth rotates at (23h and 56 minutes). As the period of rotation is related to the radius of the orbit, it needs to be at a specific height to achieve this orbital period. Geostationary satellites also need to be located over the equator.

Question 36

What is the difference between a geostationary orbit and a polar orbit?

Answer 36

A geostationary orbit always stays over one place on the earth. It has to be at a specific distance from the earth and orbits around the equator. It is used for communications and global positioning satellites A polar orbit occurs where the satellite orbits over both of the poles of the earth. It is used to that a single satelite can cover all parts of the earth during succesive orbits and is used for survalence and weather monitoring. It can be at any desired height.

Question 37

Explain why scientists were reluctant to accept the big bang theory initally

Answer 37

At first the evidence for the big bang theory was weak and there were competing theories that explained the observation such as steady state theory. Over time as the evidence for big bang theory strenghened, for example with the discovery of Cosmic Microwave Background Radiation, more scientists accepted it.

Question 38

What has happened to the rate of expansion of the universe over time since the big bang?

Answer 38

After the big bang there was inflation, a period where space expanded very quickly. After this the expansion of the universe slowed down dramatically, but now it has started to acclerate again.

Question 39

Describe the two possible fates of the universe Explain what will decide which of these fates will occur

Answer 39

1. Big crunch - the gravitational force of the universe will slow down the expansion of the universe and eventually it will contract back to a single point. This creates a cyclical universe as another big bang will happen, causing the process to repeat, this is called the cyclical universe 2. Big Yawn - The univers continues to expand forever untli eventually it is so spread out that no energy can be transferred from one place to another. This causes the universe to die a 'heat death' The big crunch will happen if the effect of gravity (from dark matter) has a greater effect than the effect of expansion (from dark energy). The big Yawn will happen if the effect of expansion outweights the effect of gravity.

Question 40

Describe how recent evidence has changed our knowledge of the big bang

Answer 40

By comparing old and new supernovas, we have recently discovered that the rate of expansion of the universe is increasing. This has caused the big bang theory to have to change, as it originally prediced that the expansion would stop and then reverse. This has led to the inclusion of dark energy into the theory

Question 41

What is dark energy? Explain how dark energy is affecting the universe

Answer 41

Dark energy is energy in the universe that we cannot detect and know very little about Dark energy affects the universe becuase the expansion of the universe is accelerating. The energy to cause this acceleration is the dark energy

Question 42

What is dark matter? Explain how dark matter is affecting the universe

Answer 42

Dark matter is matter that cannot be seen or felt except because it exerts a gravitational force on surrounding objects Dark matter is important becuase stars at the edge of the galaxy are rotating around the galactic nucleus at a much faster rate than expected, implying a that there is a greater gravitational force in galaxies compared to theat from the matter that we can see.

Question 43

What is an emission spectrum? What is an abosorbtion spectrum?

Answer 43

An emission spectra is a characteristic set of wavlennghts that are emitted by an element when it is heated up. Each element will emit a unique combination of wavlengths, so it acts like an atomic fingerprint An absorbtion spectrum is the set of wavelengths that a cold element absorbs, it is the same wavelengths for each element as the emission spectrum

Question 44

How can emission or absorbption spectra be used to work out the distance of a galaxy from us.

Answer 44

By comparing the pattern of the absorption spectra for light emitted by galaxies you can work out how red shifted the light is. Hubbles law can then be used to find the distance of the galaxy from the Milky Way.

Question 45

Describe how we have gathered evidence to discover how the solar system was formed

Answer 45

By analysing the chemical composition of the earth and discovering heavy elements such as uranium occuring naturally, we can deduce that some of the material that has formed the earth was previously part of a supernova. We know about how the sun was formed in a nebula by looking at other, younger nebula in the solar system and observing how stars are formed by looking at stars in various stages of formation