6.Space physics Flashcards
Heliocentrism
The idea that the earth orbits around the sun
Orbit
A curved path that an object follows around another object. For example, the Earth orbits the Sun.
What are the two types of experiences on earth, caused by orbits?
- Day and night
- Seasons
What causes day and night?
The Earth spins on its axis once every 24 hours.
–> For approx, 12 hours a particular spot on the earth is facing away from the sun and experiencing night.
+ vice versa.
(the sun moving across the sky is actually jut the earth rotating to/away from it)
Why years/ seasons occur (basic reason)
The earth takes just over 365 days to complete one full orbit of the sun.
This is called a year.
Most countries (aside from those near the equator), experience four seasons.
This is because of the slight (23.5) tilt of the Earth’s axis.
Why does the tilt of the earth’s axis, cause seasons.
In December, the northern hemisphere is angled away from the sun + the southern hemisphere is angled towards the Sun.
This means that the northern hemisphere experiences less sunlight, whereas the southern hemisphere experiences more sunlight.
+ vice versa in June
Working out the circumference of an orbit (under the assumption it is perfectly circular)
C = 2πr
eg.
r = distance from the centre of the Earth to the centre of the Sun
C = circumference of earth’s orbit.
Working out the speed of an object in orbit. (eg. earth around the sun)
Speed = distance/time
Speed = 2πr/time
bc C = 2πr
What is the orbital period of earth
1 year
Why does the moon shine?
It reflects the light from the sun.
How long does it take for the moon to orbit the earth
1 month
What happens during the monthly orbit of the moon?
The moon travels around the earth whilst rotating at the same rate –> That way only one half of the moon is seen by the earth.
The sun shines towards the earth and the moon. Half the moon will always be lit up.
However, if the moon is between the earth and the sun, there will be no moon (known as a new moon) bc the earth can’t see the light reflected from the sun.
If the moon is behind the earth, all of the sunshine is being relfected by the moon –> Full moon.
The Solar System
Sun
Mercury
Venus
Earth
Mars
Asteroid belt
Jupiter
Saturn
Uranus
Neptune
Dwarf planets (eg. Pluto)
Comets also occur throughout the solar system.
Found in the milky way galaxy.
Order of the planets
My - Mercury
Very - Venus
Excellent - Earth
Mother - Mars
Just - Jupiter
Served - Saturn
Us - Uranus
Noodles - Neptune
Sun
All the planets, comets and asteroids in the Solar System orbit the Sun.
Mercury
Small rocky planet
1st planet in the solar system.
Venus
Small rocky planet
2nd planet in the solar system.
Earth
Small rocky planet.
3rd planet in the solar system.
Mars
Small rocky planet
4th planet in the solar system.
Jupiter
Gas giant planet
5th planet in the solar system
Saturn
Gas giant planet
6th planet in the solar system.
Uranus
Gas giant planet
7th planet in the solar system.
Neptune
Gas giant planet
8th planet in the solar system.
Dwarf planets
Small, rocky bodies orbiting the Sun, not big enough to be called planets. Pluto is an example.
Comet
Balls of ice which orbit the Sun in elliptical orbits. When they come close to the Sun they heat up and some of the ice evaporates, becoming a visible tail.
Asteroid belt
Millions of rocks, much smaller than planets, orbiting the Sun between Mars and Jupiter.
Dwarf planet Ceres can be found in the asteroid belt.
Natural satellite
An object that orbits a planet or another body that is larger than itself.
Natural satellites are not man-made.
Pattern of planet composition, moving out of the solar system.
Four planets closest to the sun = small + rocky
Four planets further from the sun = large + gaseous (primarily made of hydrogen and helium)
Interstellar clouds
Clouds of dust and gas found in space. Interstellar means between stars, so these clouds are found in deep space. They contain the elements necessary to eventually form stars and planets.
Sometimes referred to as a nebula
How was the solar system formed?
Over billions of years, interstellar clouds of dust gradually clump together because of its own gravity.
This eventually began to spin as a disc and eventually MOST of it ignited + became the sun.
Particles in the remaining disc of dust began to clump together + combine
–> grow into larger chunks, pulled together by gravity. –> Planets
(This is called the accretion model)
At what angle is the earth tilted
23.5 degrees
Accretion model
The conceptual model for how planets are formed from a disc of material around a star. Planets and other natural satelittes form through matter clustering together due to gravity.
Accretion disk
The disc of matter which surrounds a newly formed star. Slowly, the matter clumps together due to gravity to form planets.
What was the accretion disk around the sun made from?
Many different kinds of elements…
But most common were hydrogen + helium.
Why did planets form using the materials they did and how is the accretion disk responsible?
Accretion disk around sun = several elements but mostly H and He.
Close to sun = higher temperature
–> Materials like hydrogen + helium with low boiling points couldn’t solidigy into planets.
–> Less common but heavier elements (eg. iron) = only elements that could form planets closer to the sun
–> Further from the sun, hydrogen + helium can condense nto a liquid to form planets like Jupiter, Saturn, Uranus and Neptune
–> Bc so many of these elements –> planets are much bigger.
Gravitational field strength of objects in the solar system.
More mass = Greater gravitational field strength at its surface.
–> Sun has the strongest gravitational field strength (bc it has the highest mass)
–> Why all the planets orbit the Sun
Speed of light
3 * 10⁸ m/s
Working out how long it would take for light to reach other planets…
Speed = Distance / Time
eg.
3 * 10⁸ = 7.8 * 10¹¹m / time
Time = 2600s
Effect of distance in the solar system
Further from an object = Lower gravitaitonal pull + less light
Elliptical orbits
An orbit that is not circular. The orbiting objects gets closer and further away from each other at different points in the path.
How an elliptical orbit works
The planet is closer to the star in certain areas of the orbit than others.
The planet moves faster during the part of the orbit where it was closest to the star.
Bc closer to the star = more gravitational potential energy –> converted to kinetic energy.
Travels further away –> kinetic energy = converted back into gravitational potential energy –> so slows down.
Total energy = KE + GPE
If one increases, the other will decrease.
How does orbital radius affect speed of orbit?
Mercury = closest to sun = fastest orbit
Earth = further away from the sun = slower orbit than mercury
… Bc gravitational force of attraction from the Sun is weaker at these larger distances.
What happens to the orbital duration as the orbital distance increases?
As orbital distance increases, the orbital duration also increases.
This happens because the gravitational effect of the Sun is less as you travel further from it.
What happens to temperature as the orbital distance increases.
In general, the temperature decreases as you move further from the Sun.
(Venus is the exception to this rule. Venus has a thick atmosphere which traps in a lot of the heat, making it much hotter than it would be with no atmosphere.)
What happens to gravitational field strength on the surface of the planet as mass increases?
Generally, the higher the mass of the planet, the stronger the gravitational field at its surface.
There are some exceptions to this, most notably Saturn which has a large mass but a relatively weak gravitational field. This is because Saturn has a very low density.
Describe how the density of the planets change with orbital distance?
The innermost four planets (Earth, Venus, Mars and Mercury) have much higher densities than the four gas giants (Jupiter, Saturn, Uranus and Neptune).
This is because the four rocky planets are made from dense, heavy materials like iron, whereas the gas giants are made predominantly from hydrogen and helium, two very light elements.
Star
A ball of gas which radiates energy in the form of electromagnetic waves.
Usually (unless dying) made of hydrogen + helium
eg. our Sun
What type of energy does the sun emit?
Most of its eneryg is emitted by infrared, visible and ultraviolet regions of the electromagnetic spectrum.
- Created through nuclear fusion
Nuclear fusion in stars
- Energy emitted by star comes from reactions called nuclear fusion.
- Inside the star, hydrogen atoms join together with enough force to cause them to fuse into helium atoms
- This reaction produces energy whcih is released in the form of electromagnetic waves.
–> This only happens in stable stars
–> As a star gets older –> runs out of hydrogen –> Has to fuse other elements –> more unstable
Galaxies
Galaxies are collections of billions of stars, all orbiting around a galactic centre which is usually a black hole.
Milky way
The galaxy in which our Sun and Solar System exist.
Our solar system exists towards the edge of the ‘disk’ shaped galaxy.
Measuring large distances
Large distances measured using light years.
A light year = distance travelled by light waves through the vacuum of space in one earth year.
How are stars are formed? (in-depth)
(accretion model)
All stars are born from a stellar nebula (more concentrated interstellar clouds of gas + dust)
Element hydrogen must be present in stellar nebula.
Bc of gravity, the interstellar cloud collapses upon itself + all the hydrogen (+ other elements) clump together.
Temp increases bc hydrogen nuclei fuse together
Temp continues to increase as gravity continues to pull in more material.
(This stage is called a protostar)
Protostar
The beginning of a star, where hydrogen begins to heat up and emit radiation.
Stable star
A star in which the inward force of gravity and the outward force due to the high temperature of the star are balanced.
Protostar –> Stable star
As temperature increases due to gravity, outwards force from star also increases.
Eventually force of gravity = outwards force
–> Star becomes stable
Why does a star die?
Stars remain stable for most of life
It eventually runs out of hydrogen –> Nothing more to fuse / create energy.
It can either become a red giant or a massive star.
Stellar nebula –> Protostar
The stellar nebula gradually collapses under its own gravity. As it collapses, the temperature increases, and it starts to emit light. This is a protostar.
Stars dying - Red giant
When average stars begin to run out of hydrogen, the outer layers expand, and the star becomes a red giant. When this happens to our Sun, it will grow so much that it will engulf the Earth!
Red giant –> Planetary nebula
When the red giant eventually runs out of fuel, the outer layers will spread out further while cooling down, eventually becoming a loose cloud of gas and dust.
(Despite the name, a planetary nebula has nothing to do with planets.)
Planetary nebula –> white dwarf
After the outer layers of the red giant have spread out, the core of the star remains.
No fusion happens, but the temperature is still extremely high, so it glows white and so it is called a white dwarf.
Stars dying - Massive star
If the star has a relatively high mass, around five times bigger than our Sun, it forms a massive stable star.
The force of gravity is balanced by the outward force due to the high temperature in the centre.
Massive star –> Red supergiant
When massive stars begin to run out of hydrogen, the outer layers expand, and the star becomes a red supergiant.
Red supergiants can be up to 1000 times bigger than our Sun.
Red supergiant –> Supernova
A red supergiant is so massive that it has a huge amount of gravity.
When the star finally runs out of fuel, this gravity pulls all the matter back into the centre. This creates a huge amount of pressure, which causes the star to violently explode.
This explosion is called a supernova and it is one of the brightest events in the Universe.
A supernova can create a stellar nebula, which in turn can form new stars and planets
Supernova –> Neutron star
After the supernova, the core of the star is left behind.
There is so much mass and therefore so much gravity that atoms cannot even exist and are crushed together to form a block of neutrons. This is known as a neutron star.
Neutron star –> Black hole
After the neutron star, If the star’s core is massive enough, even neutrons cannot exist because gravity is crushing them together with so much force.
All the matter in the core of the star is crushed together to a single point, creating the most dense object in the Universe, a black hole.
Two processes in which a star dies…
Red giant –> Planetary nebula –> White dwarf
Massive giant –> Red supergiant –> Supernova –> Neutron star –> Black hole
Cosmic Microwave Background Radiation (CMBR)
The microwave radiation left over from the Big Bang, which is observed everywhere in the Universe.
Big bang –> created a lot of radiation –> radiation redshifted into microwave region of EM spectrum
Calculating the age of the universe (6.2.3b)
???
How far can light travel in one year?
(What is the distance of a light-year)
3.0 * 10^8 m/s = distance / time
Distance = 9.5 * 10^15 m
Full life cycle of a star –> Explained.
1) Interstellar cloud/stellar nebula exists.
2) Gravity causes it to collapse in on itself –> Hydrogen + other elements clump together. Hydrogen nuclei fuse together.
3) Gravity pulls in more material –> more nuclear fusion –> Higher temperature.
4) Protostar created. (outwards pressure of nuclear fusion is less than gravity)
1) Eventually enough material is pulled into star so the outwards pressure of nuclear fusion is equal to gravity. (This is called a main sequence star.
2) A main sequence star can either be an ‘Average Star’ (average size) or a ‘Massive Star’ (massive size)
3) (Massive stars occur if the stellar nebula had a larger mass / more matter).
—– Average star continued —–
1) Eventually helium in the core begins being used up. The star starts fusing hydrogen in the outer shell.
2) The temperature of nuclear fusion usign hydrogen is much higher than that of helium –> Creates large outwards pressure + temperature –> Star expands into a red giant.
1) Eventually the red giant runs out of hydrogen as well and cools down (no more fusion)
2) This causes the layers to spread out even more.
3) This forms a planetary nebula (loose cloud of gas + dust).
1) Although a planetary nebula has been formed, the inner core of the star is still hot.
2) This is called a white dwarf.
—– Massive star continued —–
1) Same process in which a red giant is formed, occurs. However, the difference in mass means a red super giant is formed instead (expands even more drastically)
1) Red super giant is so large it has a lot of gravity.
2) Eventuallyt eh star runs out of fuel.
3) Large amount of gravity causes it to collapse in on itself.
4) Force of the collapse creates pressure –> Which causes a large explosion to occur (This explosion can sometimes create a stellar nebula as it flings matter out from itself)
1) Leftover core from the star after a supernova is called a neutron star.
2) (There is so much mass (and thus gravity) that atoms are crushed together to form a block of neutrons.
1) If the stars core is large enough –> gravity will be higher –> A black hole can be formed if gravity is strong enough.
Doppler effect –> Explained
An object emits sound waves at a constant frequency.
It emits a wave. It then moves towards you and emits another wave.
Since it is moving, the second wave reaches us faster. Therefore we PERCIEVE, that the wavelength has shrunk. THIS is relative to us.
As a wavelength shrinks, the pitch increases.
Therefore cars moving towards us create a large speed.
As an object moves away from us, it emits a wave.
The wave reaches us.
The object then moves further away from us and emits another wave. Since the distance between us and the object has increased, it takes longer for the wave to reach us.
Therefore the wavelength (WE PERCIEVE) has increased, and the pitch becomes lower.
The wavelength the object emits is constant (However, we experience it as changed.)
Red shift –> explained
Objects in space typically emit visibe light.
As an object moves further away from us, the wavelengths (WE PERCIEVE) expand. (This is because it takes longer for the waves to hit us)
Since red visible light has a longer wavelength, the expanded wavelength, gets percieved as red. This is called redshift.
Eventually the wavelength may expand (or be percieved to expand by us) to infrared or microwave radiation.
ADD ABSORPTION SPECTRUM
Big bang theory
The theory that the Universe started from a single point with an enormous explosion.
Cosmic microwave background radiation (CMBR)
The microwave radiation left over from the Big Bang, which is observed everywhere in the Universe.
- After Big Bang, Universe = hot –> thus a lot of radiation.
- Radiation not travelled across the universe
- Now extremely faint + redshifted to microwave region of EM spectrum.
The length of time that has occurred for can be determined by looking at galaxies as Hubble did.
Hubble constant
Hubble constant (H0) is the ratio of an objects speed in which it is moving away from earth, to its distance from earth.
H0 = v/d
v - receding speed (m/s)
d - distance from earth (m)
The numerical value of the hubble constant is 2.2 * 10⁻¹⁸ per second.
(applies to all galaxies measured + can therefore be used to estimate the age of the universe)
How it the age of the universe estimated?
H0 = v/d
v = d/t –> t = d/v
–> 1/H0 = d/v = t
t = 1/ (2.2*10⁻¹⁸) = 4.5 *10¹⁷ seconds = 14 billion years
What is the absorption spectra and how does it work?
Visible light contains several wavelengths, creating a spectrum of colours (ROY-G-BIV)
The sun emits visible light. However, chemicals int eh sun absorb certain wavelengths.
Therefore when visible light reaches the earth, certain colours / wavelengths are ‘missing’.
This creates dark lines on the absorption spectra
How does the absorption spectra connect to redshift?
When analysing light from distant galaxies, we can see that they also have colours/ wavelengths on the absorption spectra missing (in the same pattern as those on earth –> bc stars all contain same chemicals)
However, these lines have all shifted towards the red end of the spectrum.
This is because the wavelengths appear stretched because the universe is expanding and therefore the galaxy + earth aren’t moving at constant speeds.
How many metres in a light year?
9.5 * 10¹⁵ m
