Space physics

What lies at the center of the solar system

The sun is a star which makes 99% of the mass of the solar system

What is the difference between dwarf planets and normal planets

The gravitational field around planets is strong enough to have pulled in all nearby objects except natural satellites while dwarf plants gravitational field is not strong enough

What are moons

These are natural satellites that orbit around planets

What is an asteroid

This is a small rocky object that orbits the sun. The asteroid belt lies between Mars and Jupiter

What are comets

• 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

What is a nebula

A cloud of dust and gas in space

Describe the formation of the sun

• The sun is formed from massive clouds of dust and gas in space

• Gravity pulls the cloud together into a giant ball

• As the nebula collapsed the center of this ball got very dense and hot and began to rotate

• Eventually nuclear fusion was able to begin and a dense prostar was formed- our sun

Describe the forces in the sun

• 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 pressure

  • This is an outward force which is exerted from the expanding hot gases inside the star

Describe equilibrium in stars

• When the inward pull of gravity and the outward pressure acting on the star are equal the star will be in equilibrium

How does increase in temperature affect equilibrium in a star

• If the temperature of a star increases, the outward pressure will also increase

  • This will cause the star to expand

How does decrease in temperature affect equilibrium in stars

• If the temperature drops (because, perhaps, the rate of fusion has slowed) the outward pressure will also decrease

  • This will cause the star to contract

Describe fusion in stars

• All the naturally occurring elements, apart from hydrogen, have been formed by nuclear fusion in stars

• Nuclear fusion occurs when two light nuclei collide at high speed and join to create a larger, heavier nucleus

• When the Universe was first formed, 13.8 billion years ago, the only element present was hydrogen

• If two hydrogen nuclei collide with enough energy they will fuse into a helium nucleus

  • For example, the nuclei of two different isotopes of hydrogen (protium and tritium) can join to form a helium nucleus by the process of nuclear fusion

  • The process of nuclear fusion releases energy

    • The energy is released in the form of heat and light

Describe the formation of new elements lighter than iron in a star

• 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

Two helium nuclei fusing together to form a beryllium nucleus

• The beryllium nucleus could then fuse with a helium nucleus to form a carbon nucleus

A beryllium nucleus fusing with a helium nucleus to form a carbon nucleus

• Elements lighter than iron are formed in fusion reactions like the ones above

Describe the formation of elements heavier than iron in a star

• Elements heavier than iron are produced in supernovaexplosions

  • 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 reactions get thrown out and combine with the neutrons to form heavier elements

What is life cycles after of a star same size as the sun

• Stella nebula→ protostar→ main sequence star → stars about the same size as the sun→ red giant star → planetary nebula → white dwarf → black dwarf

Describe the nebula stage of a star

1. Nebula

• All stars form from a giant cloud of hydrogen gas and dust called a nebula

Describe protostar stage

2. Protostar

• The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas, known as a protostar

• As the particles are pulled closer together the densityof the protostar will increase

  • This will result in more frequent collisions between the particles which causes the temperature to increase

Describe main sequence star stage

• Once the protostar becomes hot enough, nuclear fusion  reactions occur within its core

  • The hydrogen nuclei will fuse to form helium nuclei

  • Every fusion reaction releases heat (and light) energy which keeps the core hot

    during the main sequence the star is in equilibrium

Describe red giant stage

• After several billion years the hydrogen causing the fusion reactions in the star will begin to run out

• Once this happens, the fusion reactions in the core will start to die down

• This causes the core to shrink and heat up

  • The core will shrink because the inward force due to gravity will become greater than the outward force due to the pressure of the expanding gases as the fusion dies down

• A new series of reactions will then occur around the core, for example, helium nuclei will undergo fusion to form beryllium

• These reactions will cause the outer part of the star to expand

• It will become a red giant

  • It is red because the outer surface starts to cool

Describe planetary nebula stage

• Once this second stage of fusion reactions have finished, the star will become unstable and eject the outer layer of dust and gas

  • The layer of dust and gas which is ejected is called a planetary nebula

Describe white dwarf stage

• The core which is left behind will collapse completely, due to the pull of gravity, and the star will become a white dwarf

• The white dwarf will be cooling down and as a result, the amount of energy it emits will decrease

Describe black dwarf stage

• Once the star has lost a significant amount of energy it becomes a black dwarf

• It will continue to cool until it eventually disappearsfrom sight

What are the stages of the lifecycle of a star larger than the sun

• stellar nebula→ protostar→ main sequence star→ stars much bigger than sun → red super giant star → supernova→ neutron star or black hole

Why do stars larger than the sun have shorter lifespans

• 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

• The life cycle of a star bigger than the Sun starts in the same way as a solar mass star

Describe red super giant stage of a star larger than sun

• Eventually, the main sequence star will reach a stage when it starts to run out of hydrogen gas in its core

• Once this happens, the fusion reactions in the core will start to die down

• This causes the core to shrink and heat up

  • The core will shrink because the inward force due to gravity is greater than the outward force due to the pressure of the expanding gases

• A new series of fusion reactions will then occur around the core, for example helium nuclei will undergo fusion to form beryllium

• These fusion reactions will cause the outer part of the star to expand and it will become a super red giant

  • A super red giant is much larger than a red giant

Describe the supernova stage of a star larger than the sun

• Once the fusion reactions inside the red supergiant finally finish, the core of the star will collapse suddenlycausing a gigantic explosion

  • This is called a supernova

• At the centre of this explosion a dense body, called a neutron star will form

• The outer remnants of the star will be ejected into space during the supernova explosion, forming a planetary nebula

Describe the neutron star or black hole stage of stars larger than the sun

• In the case of the biggest stars, the neutron star that forms at the centre will continue to collapse under the force of gravity until it forms a black hole

  • A black hole is an extremely dense point in space that not even light can escape from

What is a supernova

supernova is a bright and powerful explosion that happens at the end of a massive star's life

• It occurs when the star is bigger than the Sun

What happens during a supernova

• The explosion releases a large amount of energy

• During a supernova, all of the elements which were produced by the fusion reactions are exploded outalong with neutrons

• The neutrons combine with the elements to form even heavier elements

• These elements are ejected into the universe by the supernova explosion and form new planets and stars

  • Since Earth contains many heavy elements up to Iron, this is proof that it must have once been made from the remains of a Supernova

What are the orbits of different objects in solar systems

Describe the circular orbit of bodies in space

• smaller body or object will orbit a larger body

• In order to orbit a body such as a star or a planet, there has to be a force pulling things towards that body

  • Gravity provides this force

• The gravitational force exerted by the larger body on the orbiting object is always attractive

• Therefore, the gravitational force always acts towards the centre of the larger body

• The gravitational force is the centripetal force as it will cause the body to move and maintain in a circular path

Describe the circular motion of an object in orbit

• Planets travel around the Sun in orbits that are (approximately) circular

• Objects in circular orbit are travelling at a constant speed

• The orbit is a circular path, therefore the direction in which the object is travelling will be constantly changing direction

• A change in direction causes a change in velocity

• Acceleration is the rate of change of velocity, therefore if the object is constantly changing direction then its velocity is constantly changing and so the object in orbit is accelerating

• A resultant force is needed to cause an acceleration

• This resultant force is gravity and it must act at right angles to the instantaneous velocity of the object to create a circular orbit

  • This is always towards the centre of the orbit

  • The instantaneous velocity of the object is the velocity at a given time

What are the similarities in the way different planets orbit the sun

• Their orbits are all slightly elliptical (stretched circles) with the Sun at one focus (approximately the centre of the orbit)

• They all orbit in the same plane

• They all travel the same direction around the Sun

What are the differences in the way different planets orbit the suj

• They orbit at different distances from the Sun

• They orbit at different speeds

• They all take different amounts of time to orbit the Sun

Define orbit of moons

• Moons will orbit planets in a circular path

• Some planets will have more than one moon

• The closer the moon is to the planet:

  • The shorter the time it will take to orbit

  • The greater the speed in the orbit

Describe the orbit of artificial satellites

• A satellite needs to travel at a specific speed to maintain a circular orbit at a particular distance from the object

Describe what happens when the speed of an artificial satellite is too big

• If the speed of the satellite is too big:

  • The radius of the orbit will increase and the satellite will spiral into space

  • This is because the gravitational attraction cannot provide enough force to keep it in orbit

What happens if the speed of a satellite is too small

• If the speed of the satellite is too small:

  • The radius of the orbit will decrease and the satellite will move towards the object it should be orbiting

  • This is because the gravitational attraction is too strong to maintain a constant orbital radius

How do satellites obtain a stable orbit

• If an artificial satellite is to change the radius at which it is orbiting then the speed at which it is travelling must change

• To maintain a stable orbit:

  • If the speed increases the radius must decrease

  • If the speed decreases the radius must increase

Describe orbit of a comet

• The orbits are highly elliptical (very stretched circles) or hyperbolic

• This causes the speed of the comets to change significantly as its distance from the Sun changes

• Not all comets orbit in the same plane as the planets and some don’t even orbit in the same direction

• As the comet approaches the Sun, it loses gravitational potential energy and gains kinetic energy

• This causes the comet to speed up

• This increase in speed causes a slingshot effect, and the body will be flung back out into space again, having passed around the Sun

• As it moves away from the Sun the body will slow down, eventually finishing its orbit and falling back into towards the Sun once more

• In this way, a stable orbit is formed

Describe the wavelength of a moving object

• A moving object will cause the wavelength, λ, (and frequency) of the waves to change:

  • The wavelength of the waves in front of the source decreases (λ – Δλ) and the frequency increases

  • The wavelength behind the source increases (λ + Δλ) and the frequency decreases

  • This effect is known as the Doppler effect

What is the Doppler effect

The change in frequency or wavelength due to the relative motion between a source and an observer

Describe how the Doppler effect affects light

• The Doppler effect also affects light

• If an object moves towards an observer, the wavelength of light decreases

  • This is known as blueshift as the light moves towards the blue end of the spectrum

• If an object moves away from an observer, the wavelength of light increases

  • This is known as redshift as the light moves towards the red end of the spectrum

What is red shift

The observed increase in the wavelength of light due to the source moving away from the observer

Describe the motion of light from a star

Light from a star that is moving towards an observer will be blueshifted and light from a star moving away from an observer will be redshifted

Light coming from the sun compared to light coming from a distant galaxy

Light from a star that is moving towards an observer will be blueshifted and light from a star moving away from an observer will be redshifted

Describe how red shift proves the Big Bang right

• The diagram also shows that the light coming to us fromdistant 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

Describe the Big Bang

• 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 is the evidence of the Big Bang

• By observing the light spectrums from supernovae in other galaxies there is evidence to suggest that distant galaxies are receding (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 slowerspeed, closer to the source of the explosion

• If you were to travel back in time and compare the separation distance of the galaxies they would become closer and closer together until the entire universe was a single point

• If the galaxies were originally all grouped together at a single point and were then exploded we would see a similar effect

  • The galaxies that are moving fastest would move the furthest - the distance they move would be proportional to their speed

  • The galaxies that are moving slowest would move the least

What are the observations not understood about the universe

• Evidence from the rotation and motion of galaxiessuggests that there is much more matter in the Universe than we are able to account for

• This unseen matter is given the name dark matterand 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

How does the earth gravitational force affect motion of satellites

• gravitational force causes the satellite to accelerate towards the earth

• This changes the direction of motion but not speed

• So changes the velocity of the satellite

How does red shift prove the Big Bang theory