PP1 TOPIC 5

What does the solar system contain

Sun, 8 planets, their natural satellites, dwarf planets, asteroids, comets

Order of planets going from the sun

Mercury » Venus » Earth » mars » Jupiter » Saturn » Uranus » Neptune

Natural satellites

Earth has one natural satellite called the moon whilst larger plants such as Saturn and Jupiter have many natural satellites

A dwarf planet

Pluto used to be classed as a planet but due to its small mass and location in space it was degraded to a dwarf planet in 2006

Asteroids

Most asteroids form a ring of rocks that orbits the sun and is found between Mars and Jupiter

Comets

Travel in highly elliptical paths and come from many millions of miles always

What has been changing over time

Ideas about the structure of the solar system

Old idea

Many early people thought that the Sun and all the planets moved around the earth . Geocentric (Earth- centred) model was published which tried to explain the motions of the planets , Earth is at the centre and the sun and the planets orbit the earth

Current idea

The Earth and planets are in orbits around the sun- heliocentric model (Sun-centred model) Sun is at the centre and planets orbit the sun

Suggest why some planets have been discovered more recently than others

Greater distance makes them dimmer; recent developments in telescope allow these to be seen

Natural satellites

Formed by natural processes e.g 8 planets in solar system which orbit the sun

Moons which orbit planets

Comets which orbit the sun

Artificial satellites

Manufactured and have been launched in space from earth by using rockets

Example 1

Satellites in geostationary orbits around the Earth being used for global positioning sat systems (GPS)

Example 2

Sat in lowers polar orbits round earth being used for wearher monitoring , military, spying or earth observ purposes

Example 3

Sat sent from earth to orbit and monitor the sun other planets or aestroids in the solar system

Orbits in general

Bodies of lower mass will travel in orbits around bodies of higher mass

Type of orbit 1

Artif satellites orbiting the Earth and plants orbiting the sun tend to move in circular or non circular orbits

For circular orbits

The gravit force acting on the body in a circular orbit willl be the same at each point of the orbit since radius is fixed , speed of orbit will not change but velocity will be constantly changing be wise direction is constantly changing

Orbit type 2

Comets travel in highly elliptical orbits around the sun, speed and velocity of comet change constantly, gavit force of the sun acting on comet gets weaker as it gets further from sun and will travel more slowly when it is far form the sun and faster when it is closer to sun

Compare motion of earth Jupiter Saturn as they orbit the sun

All 3 plants travel in circular orbits and have a constant speed and a changing velocity , as distance from sun increases orbit speed decreases so earth has higher orbital speed than Jupiter which has a highe orbital speed than Saturn

Planets in solar system are also

in stable orbits → if earth’s OS increases then the GVF from the sun would not keep it in orbit and it would fly out of its orbit into a new orbit of greater radius

If earth’s OS decreases

Sun’s gravit field would cause it to fall towards it into a new orbit of smaller radius

Explain how speed and velocity of a comet changes over the course of one orbit

Speed is greatest near the sun and velocity changes the most nearest the sun as direction changes most when near away the sun , velocity and speed are lower when further from the sun

Explain what might happen to a GPS sat if it’s orbital speed changes

OS increases → radius of orbit decreases as centripetal force exceeds that of the GRAVIT pull

OS decreases → radius of orbit increases as grabit pull greater than centripetal force

State nature of sped and velocity of a body that is moving in a circular orbit

Speed of body in circular orbit is constant but velocity is changing as the direction of body is constantly changing

First theory about the universe

BB theory: the whole UNI started out as a tiny particle 13.8B years ago, the universe expanded form this point in space and the UNI is still expanding today

Theory 2

The steady state theory: the universe has always existed it is expanding and new matter is being created as it expands

Explain the concept of red shift

When objects that emit light such as galaxies are moving away from us then the light they emit is red shifted which means the wavelengths from them when detected back on Earth will be ‘stretched’

What does that mean

The spectral lines will be shifted further to the red end of the spectrum compared with a stationary object observed on Earth

the speed of the galaxy

The faster the galaxy is travelling away from us The more these lines will be shifted to the red end of the spectrum since the furthest a galaxies show more red shift than those nearer to us suggesting universe is expanding

CMB - cosmic microwave background radiation

Is the ‘echo’ of the BB

Explain

At the time of the BB this radiation would have been incredibly hot and intense but over time this radiation has cooled and is now very weak at a temp of -270°C close to absolute zero

How does it act as evidence

The fact that CMBR is detected in all directions and has the temp that it does is evidence that the UNIV started with a BB almost 14B Years ago

Which theory is currently the accepted model for the beginning of the UNIVN

BB because it has the most evidence supporting it

Explain

Although red shift is evidence for both the SS and the BB theory it is the CMBR that provides the key evidence for the BB theory

CMBR as evidence r

Radiation is detected by radio telescopes and comes from all over the sky. The BB theory says that this radiation was released at the beginning of the Universe

Galaxy A is further away than galax B explain the similarities and differences you would expect in the light from these galaxies as a result of their movement

The universe is expanding so the galaxies are moving away from us and the light from them will be red shifted. More distant galaxies are moving away from us faster so their light will have more red shift. Galaxy A is further away from galaxy B so light from it will have a greater red shift

Explain how red shift suggests the universe is expanding

The light received on earth from most galaxies is red shifted which means most galaxies are moving away from us. The furthest galaxies from us have the greatest red shift so are moving away from us faster which suggests universe is expanding

Doppler effect

When a wave source is moving relative to an observer there is a change in the observed frequency and wavelength of the waves

For example, away from observer

When siren is moving away from the observer this stretches the sound waves out giving it a longer wavelength and so a lower frequency the pitch therefore sounds lower

For example towards observer

The siren is travelling towards an observer this compresses the sound waves making the frequency higher and so the pitch of the siren sounds higher to the observer

However the driver of the car with the siren

He is not moving relative to the siren so the pitch he hears is the same all the time as it would be for eam external observer if the car was stationary

What does the Doppler effect occur for

Light waves as well as for sound waves

For example for light

A light source moving away from an observer will have a greater wavelength and a lower frequency ‘red shifted’

Light source moving towards observer will have a smaller wavelength and a higher frequency ‘blue shifted’

Describe an example for Doppler effect for sound waves

Siren changing its frequency as it lives relative to an observer frequency greater for approach of the observer and lower on recession from observer

Describe an example of Doppler effect for light waves

Red shift of light/ spectral lines for light from a galaxy or star that is moving away from us

Suggest how the speed of a galaxy can be determined from absorption lines its spectrum

Absorption lines in the spectra of the light from the galaxy can be compared with the corresponding absorption lines of a stationary source. The difference in the position/ wavelength/ frequency can be used to calculate the speed of the galaxy

How was it discovered that the light reaching the earth from galaxies is red shifted

By looking at the spectral lines in the absorption of stars that are moving away from us. The lines of the galaxy that are red shifted the most is moving away from us the fastest

What happens to stars

They go through a number of stages in life but their eventual fate depends on their mass

The sun

It was formed about 4.6B years ago and is nearly half way through its life

Low mass stars

Stars with masses up to 4 times the mass of the sun

First step in a life cycle of a low mass star

The flow of dust and hydrogen gas (nebula) is pulled inwards by the force of gravity. As the dust and gas contracts the nebulae gets hotter since work is being done on it

Second step

Eventually the dust and gas becomes hot enough for the hydrogen nuclei to fuse. Nuclear fusion leads to heavier helium nuclei being produced and large amounts or energy being released

What will start to happen

The star will begin to give out light and is now a main sequence star, stars are MSS’s for most of their lives

Forces

The inwards force of gravity is balanced by an outward force of thermal expansion

Third step

When most of the hydrogen gas has been converted to helium the star will expand and become a red giant

What else will happen

When the core of this star collapses other heavier elements are formed

fourth and last step

Eventually all nuclear fusion stops due to the elements that cause fusion being used up and the star collapses to become a white dwarf

Whereas a star with a much higher mass than the sun

Will follow the Sam efurst stages of the life cycle but each stage is shorter

Another difference

When most of the hydrogen is used up it forms a super red giant and at the end of this stage the sun will explode as a supernova

after

If what remains after explosion is less than 4x the mass of the sun it will be pulled together by gravity to form a very small dense star called a neutron star

More massive remnants form black holes

Explain how the fate of a low mass star is different from that of a high mass star

A low mass star will move off the main sequence and expand to become a red giant before cooling and contracting to become a white dwarf. A high mass star will move off the main sequence become a super red giant and explode in a supernova. The mass that is left in the core will become a very dense neutron star or a black hole

Stages in the life cycle of a low mass star

gravitational attraction of dust and gas » main sequence star » red giant » white dwarf

Stages in a life cycle of a high mass star

Same until main sequence » followed by red supergiant and supernova explosion » followed by a gravitational collapse to a neutron star for a massive star » to a black hole for a supermassive star

What happens to the white dwarf

It’s temp increases despite it losing thermal energy

Explain

Star radiates thermal energy as it loses heat but gains temp due to work being done it by gravitational collapse which raises its temp

Explain the role of gravity and thermal expansion

Gravity pulls dust and gas together to form a nebula leading eventually to fusion so thermal pressure balancing this when a main seequence star due to radiation pressure from fusion until thermal radiation pressure exceeds the pull of gravity at the end o the star’s main sequence life and it expands

ONSERVING UNIV

Methods used have changed, originally observ were made from the earth now there are telescopes in space to observe univ from above earth’s atmosp

The first scientists

Explored the univ by observing the visible light emitted by the stars and more discoveries were made after telescopes were invented

earlier vs modern telescopes 1

Greater magnification → can observer galaxies that are further away

Recording observ using photography or digital cameras → we can gather more data

Can be made with greater precision → we can get clearer images

Telescopes that can detect other parts of the EM spec→ can observe objects in space that emit more radio waves , infrared , UV, X rays than visible light

Some parts of the EM spectrum

Are absorbed by earth’s atmosphere

Therefore

Telescopes used to observe these wavelengths of radiation Must be put on satellites in space

For example

UV telescopes need to be placed in orbit to detect UV radiation whereas e.g. radio waves can reach us from space and be detected by radio telescopes on earth

Suggest why CMBR was detected on earth

The longer wavelength microwaves that form the CMBR are not absorbed by earth’s atmosp

Exmaplin why an X ray telescope needs to be placed In orbit

X rays are a of bed by earth’s atmos so cannot be detected by earth based satellites

Explain why visible light telescopes can be based on Earth or in space

Certain WL of visible light can penetrate earth’s atmosph so can be detected by earth based telescopes wherrsss other awls of visible light are absorbed by atmosph so cannot be detected on earth and this requires telescopes to be placed above earth’s atmosph in space

Explain how developments in modern telescopes have improved our knowledge of Univ

Greater magnif→ see further

Record data digitally → gather more data

Greater precision → clearer images

Detect other EM waves instead of light → observe other objects that emit other types of EM waves

EXAM Qs

Wavelength of light emitted from distant galaxies is different when light is detected on earth explain how this difference in wavelength shows universe is expanding

there is an increase int eh wavelength of light ACC wavelength stretches/ red shift

• shows galaxies are moving away from Earth

State what causes nebula to collapse -

gravitational force

Explain how its presence provides evidence for big bang theory

• The Big Bang theory has a beginning or initial explosion

• That realises radiation

State what it meat by cosmic background radiation

• Radiation that comes from all over the sky

Explain how red shift provides evidence for big bang theory

• big bang has expanding universe

• With a galaxies moving away from each other ACC the further away they are the greater their speed

Describe what is meant by red shift

• Wavelength increases

• As the star moves away from us ACC spectral lines move to the red end of the spectrum

Long time ago scientists believed Earth was at the Center of the solar system evidence proved that sun is at the centre of the plane system state one other idea about the solar system that has changed over time

• the earth rotate

• Planets have moons

• Orbits are elliptical

• Pluto is no longer a planet

• Planets orbit the sun

Explain why nebula stops collapsing as it becomes a main sequence star

• heavier causing increase in temp ACC increase in pressure or density

• Until hot enough for fusion ACC hydrogen to form helium / nuclear reactions

• Until abalnve between gravity and fusion / thermal

Wavelength of spectral line measured for a more distant galaxy was greater than wavelength of less distant galaxy explain how that provides evidence that universe is expanding

• the red shift value will be larger / longer wavelength

• The galaxy is moving away at a higher velocity

Observations of the Universe can be made using telescopes on Earth explain why some telescopes are located on satellites that orbit the Earth

• telescopes are above Earth/ outside earth’s armsophere

• Less interference from dust/ clouds

• Wavelengths that are absorbed by Earth’s atmosphere

• Can view the whole sky

Describe how light from distant galaxies shows universes is still expanding

• wavelength of light appears to increase

• ACC red shift shows galaxy moving away

Simailritt and difference between steady state and big bang

• both have expanding universe

• Steady state theory dewy upend the continual formation of new matter the BB theory doesn’t

State how the brightness of a main sequence star changes with its temp/:

greater the temp the higher the brightness

Stars how the brightness of a main sequence star changes with its mass

the greater the mass the higher the brightness

Explain how a nebula could revolve into a main sequence star

• nebula is a cloud of gas/ dust

• Gas / atoms pulled together

• By gravitational force

• Temp increase

• Hot enough for nuclear fusion

Describe the process that occurs to produce conditions necessary for nuclear fusion in a new star

• nebula collapses

• Under gravity

• GPE converted into KE or very high temps / pressures reached