Topic 7- Astronomy Flashcards
What is our solar system made up of ?
Moons
Planets and dwarf planets
The sun
Asteroids and comets
What galaxy contains our solar system?
The Milky Way
What do moons orbit ?
around many of the planets.
What are moons called ?
natural satellites.
What to planets and dwarf planets orbit around ?
the Sun
What are the 8 planets in our solar system ?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (Pluto is a dwarf planet).
What is a terrestrial planet ?
a planet that is composed primarily of silicate rocks or metals.
What are the terrestrial planets ?
Mercury, Venus, Earth and Mars
What is a gas giant ?
a large planet composed mostly of gases, such as hydrogen and helium, with a relatively small rocky core
What are the gas giants ?
Jupiter, Saturn, Uranus and Neptune are gas giants.
What is the only star in our solar system?
The Sun
What do comets and asteroids orbit around ?
the Sun
Briefly how was the sun formed ?
from a cloud of dust and gas (called a nebula). The forces of gravity pulled the dust and gas together.
Describe the formation of the sun ?
The gas and dust collapsed.
The cloud suddenly decreased in volume as the pressure in the cloud increased.
This formed a protostar
Materials continued to collide (come together) until the temperature and pressure were high enough for hydrogen nuclei to start fusing and form helium (in nuclear fusion).
The star then went into a stable period, called a ‘main star sequence’.
The energy released from the nuclear fusion in the Sun keeps the Sun’s core hot.
What phase is the sun in at the moment ?
its stable main sequence phase.
What is happening in the suns current phase (stable main sequence phase) ?
In this phase, the outward force of the energy released by nuclear fusion (thermal expansion forces) is balanced by the force of gravity pulling the Sun inwards.
In the Sun, what process creates a force outwards, balancing the inward force of gravity?
Nuclear fusion
What are the two important ideas that have been put forward throughout history about the structure of the Solar System ?
Heliocentric model
Geocentric model
What does the heliocentric model of our solar system propose ?
the Sun is at the centre of the Solar System (helio = Sun, centric = centre).
The Earth and other planets orbit around the Sun.
What does the geocentric model of our solar system propose ?
the Earth is at the centre of the Solar System (geo = Earth, centric = centre).
Everything else in the sky was believed to orbit the Earth.
Why do we now believe in the heliocentric model of our solar system?
Thanks to observations by Galileo and other technological advances
Why did people used to believe in the geocentric model of our solar system ?
People didn’t have telescopes, so they saw everything travel across the sky in the same way every day
What model of the Solar System do we believe to be true today?
Heliocentric
What does gravity vary with ?
mass
Is the acceleration due to gravity , g, smaller or larger for a smaller object ?
is smaller for a smaller object.
What does weight depend on ?
Gravity
Is your weight less or more on a smaller object ?
your weight is less on a smaller object
Do you weigh less on the Moon or the Earth ?
The moon as it is smaller
Why do you weigh less on the moon then on earth ?
The weight of an object is its mass multiplied by g.
Therefore, the weight of an object varies depending on where you are.
Because the Moon has a smaller mass than the Earth, and therefore has a smaller value of g, your weight on the Moon is less than your weight on Earth.
Why is the value of gravity larger on earth then the moon ?
The acceleration due to gravity, g, varies depending where you are.
The larger the body of mass, the larger the gravitational pull.
The value of g is therefore larger on the Earth than on the Moon (the Earth is bigger than the Moon).
How are all things kept in orbit ?
by gravity
All things in orbit also travel in circular motion (fact)
What orbit the earth ?
Artificial satellites
What is stable orbit ?
If the speed of the object in orbit changes, the radius of the orbit also changes.
If the speed increases, the radius of the orbit decreases.
If the speed decreases, the radius of the orbit increases.
This explains why planets closer to the sun travel at a faster speed
What happens when the radius of an object in orbit decreases?
Speed increases
What is the weight of an object equal to?
Mass x gravitational field strength
Are planets closer to the sun travelling at a slower or faster speed ?
faster speed.
What happens when the radius of an object in orbit increases?
Speed decreases
If the body of mass is larger what does this mean for gravitational pull ?
The larger the body of mass, the larger the gravitational pull.
What does the life cycle of a star depend on ?
its size
How do all’s stars begin their life cycle ?
the same way as the Sun:
Gravity pulls nebulae (more than 1 nebula) together to form a protostar
This protostar then becomes a main sequence star
If a star is about the same size as the Sun, what’s it’s lifecycle like ?
a collapsing nebula, becomes a main sequence star, then a red giant, then shrinks to a white dwarf, then forms a black dwarf.
How is a main sequence star formed ?
Protostar —> main sequence star
hydrogen nuclei are fused together to form helium.
This releases energy as heat and light
How is a red giant formed ?
Main sequence star—> red giant
Eventually all the hydrogen fuel runs out.
The star then cools and expands, becoming a red giant.
The star then starts to fuse together helium nuclei to release energy.
How is a white dwarf formed ?
Red giant —> white dwarf
As the helium fuel runs out, the outward forces reduce in size and the star collapses inwards.
This causes its temperature to increase.
A white dwarf is formed, which is the hot core of the star.
How is a black dwarf formed ?
White dwarf —> black dwarf
When the star completely cools, the star becomes a black dwarf.
A black dwarf doesn’t emit (send out) any light or heat.
If a star is bigger than the Sun, what’s its lifecycle like ?
a collapsing nebula, becomes a main sequence star, then a red supergiant, then explodes in a supernova, then forms a neutron star or a black hole.
How is a red super giant formed ?
Nuclear fusion changes more and more of the star’s mass into energy.
The star expands into a red supergiant.
How is a supernova formed ?
The largest stars explode in a supernova.
A supernova produces elements heavier than iron and scatters them throughout the universe.
How is a black hole or neutron star formed ?
The supernova leaves behind either a black hole or a neutron star after exploding
What does a main sequence star become when the hydrogen fuel runs out?
A red giant
The balance between what two main processes rule the life cycle of stars ?
thermal expansion and gravitational collapse
If forces due to thermal expansion are larger than gravitational forces what happens to the the star ?
the star will expand
If forces due to gravity are larger than thermal expansion forces,what will happen to the star ?
the star will shrink/collapse
Main Sequence stars, like our Sun, have what processes in a delicate balance, meaning the Sun is stable (for now) ?
Thermal expansion and gravitational collapse
The fusion processes in stars produce what ?
all of the naturally occurring elements.
What elements do all stars fuse ?
All stars fuse hydrogen nuclei into helium in nuclear fusion
What do large stars form ?
Larger stars fuse hydrogen nuclei into lithium and other light metals
What do supernovas form ?
A supernova produces enough energy for hydrogen nuclei to form elements heavier than iron
What are the two principal theories about the origin of the Universe ?
the Big Bang model and the Steady State model
What does the Big Bang model propose ?
To begin with all the matter and energy in the Universe was compressed into a single point.
This point suddenly exploded and started to expand.
Just after the Big Bang, the Universe was extremely hot and dense.
The Universe is still expanding to this day
What does the steady state model suggest ?
that the Universe has always existed in the way it is now and always will exist this way.
It says that as the Universe expands, new matter is created so that the density remains the same.
This model implies that the Universe has neither a beginning or an end.
It does not account for the cosmic microwave background (CMB).
Why is the Big Bang model the most supported (correct in model in GCSE) ?
This model gives a finite age for the Universe: just under 14 billion years.
The Big Bang theory is currently the accepted model of how the Universe began.
There is more evidence to support it than the Steady State model.
What is a piece of evidence of red-shift ?
red-shift
What is the Doppler effect ?
the phenomenon of the observed wavelength and frequency of waves changing when the source of the waves is moving with respect to an observer
The Doppler effect can be experienced with what types of waves ?
all types of waves.
The wavelength and frequency of the waves do not actually change.
When the source of the waves is approaching, what happens to the frequency?
the frequency shifts upwards for observers
When the source of the waves is receding, what happens to the frequency?
the frequency shifts downwards for observers.
What is the red shift effect ?
When light from distant objects in space becomes shifted towards the red end of the spectrum.
As an object moves away from us, the wavelength of light that the object emits (sends out)
gets longer.
The light gets redder because red has the longest wavelength of the visible colours.
The faster the object is moving away from us, the longer its wavelength gets and the redder it appears.
What is evidence for the expansion of the universe?
Light from distant galaxies in space is red-shifted.
The further a galaxy is from Earth, the greater the red-shift.
This means that the further away a galaxy is, the faster it is moving away from us.
This is evidence that the universe is expanding.
Red-shift provides evidence for the Big Bang theory as it shows that all objects in the universe are moving away from one another.
This suggests that the objects began from a single point, the point at which the Big Bang occurred.
The Steady State model also accounts for red-shift because it states that new matter is being created to account for the expanding Universe.
