Topic 7- Astronomy Flashcards
Why does the weight of objects change on different planets? e.g the Earth and the moon
- As F =G(mass1 x mass2)/Distance ^2
- G is a constant 6.674
- Meaning an object with LESS MASS (the moon) will have a SMALLER GRAVITATIONAL force (than the earth)
- As Weight= Gravitational field strength x mass
- An object on the moon (with the same mass) will weigh less
What is the gravitational field strength of the moon?
- 1.6 N
What is the gravitational field strength of the Earth?
- 9.8 N
- 10N
What is the (our) solar system made of?
- The sun
- Eight planets
-Dwarf planets - Natural sateleits (moons, asteroid, comets)
What are the names of the planets in order?
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
- (Pluto, dwarf)
How have ideas surrounding the solar system changed over time?
Geocentric- idea that the Earth was the centre of the solar system, and the sun, moon and planets orbited
Heliocentric- Idea that the sun is at the centre of the solar system, that the planets orbit it, and moons orbit the planets
What did the geocentric model not prove?
- Why planets changed brightness ( because they are not always the same distance from Earth)
- Jupiter and mars appeared to move backwards sometimes
- Why moons seemed to orbit planets (not everything orbited the Earth)
What in our solar system have a circular orbit/ slightly elliptical?
- Moon
- Planets
- Asteroid
What in our solar system have a highly elliptical orbit?
- Comets
Low Earth orbits: Height, speed, time to orbit, use
- 160 Km -> 2000km above Earth’s surface
- 7780 m/s
- 1.5/2 hours to orbit
- ISS (international space station)
- Communications
Polar Orbit: Height, speed, time to orbit, use
- About 160- 2000km above Earth’s surface
- 7500 m/s
- 1.5 hours
- Goes over poles
- Monitors weather, used for spying/image taking
Geo-stationary: Height, speed, time to orbit, use
- 35,900 km above Earth’s surface
- 3000 metres/s
- 24 hours
- Communications, television, weather
Elliptical: Height, speed, time to orbit, use
- Faster closer to the Earth
- Communications
How does a circular orbit due to gravity mean change in velocity but not speed?
- Gravity acts as the CENTRIPETAL force keeping the object in a circular orbit (changes linear direction)
- Velocity is a VECTOR quantity and changes as DIRECTION CHANGES
- Speed is a scalar quantity
What is the equation for the (centripetal) force in a circular motion?
F= mv^2/ radius
Explain how, for a stable orbit, the radius must change if
orbital speed changes (qualitative only)
What happens when the radius changes in a stable orbit (same centripetal force)?
- As f=mv^2/r
- If the velocity changes, but the mass and force remain constant
- Radius must change to keep the constant
- If speed increases, radius must increase
- If speed decreases, radius must decrease.
What happens when the speed of a satellite decreases?
- Falls out of orbit, towards the centre (Earth) by gravity
- Gains speed when accelerating towards the Earth
- Stabilises as speed begins to increases and radius decrease for the F and M to be constant (F=mv^2/r)
Do objects in a lower orbit feel more gravity?
- Yes
- Lower radius means the object feels more gravity and therefore has to move faster
What happens if a satellite is moving too fast?
- Force of gravity cannot keep it in circular motion as it is too fast
- Moves off into space
- 11,200 metres/sec
Why are v and r always inversely proportional?
not for centripetal force
- Force felt= g(m1xm2)/r^2
- Force= mv^2/r
simplified
v^2= g(m1, the larger body’s mass)/ r
Therefore if v is to increase, r has to decrease as gravity (6.67) and mass are constant
What in the equation F=mv^2/r changes when radius increases?
for centripetal force
- V and R are directly proportional ( v^2= g(6.67) x m1/ radius
- When Velocity increases radius has to increase
- meaning force felt is NOT CONSTANT
- F also DECREASES.
Steady state: How the world began, Expansion, Density
- Always existed
- New matter is created by expansion
- Density remains the same as new matter (mass) is being created at the same rate of expansion (volume)
Big bang: How the world began, Expansion, Density
- All universe (abt 14 billion years ago) was a very small and dense region which exploded
- Explosion caused rapid continuous
expansion - Density decreases as no new matter (m) is created but the universe (v) is expanding
What is red shift?
- Spectrum of colours absorbed by (our atmosphere) are more red shifted on the spectrum
- As light travels to us, space expands and thus the light’s wavelength increases
- Causes more red shifted light to travel to us (thus more red shifted light is absorbed)
What is CMB radiation?
- Cosmic microwave background radiation
- Earliest form of light emmitted
- Radiation emitted from all directions
- As space expands the wavelength of CMB increased into microwaves
How does red shift prove both steady state and big band?
- Both believe universe is expanding
- Steady state believes universe is expanding and new mater is being created between already existing places
What does cmb prove?
- The big band theory
- That all matter came from one place
What happens to an observer when the object emitting light/ sound is heading towards us?
- Higher frequency/ lower wavelength
- Purple/ blue
- Higher pitch
What happens to an observer when the object emitting light/ sound is away from us?
- Larger distance between waves
- Higher wavelength, lower frequency
- Red shifted colour
- Lower pitch
Why the further away a galaxy the more red shifted it is?
- More distance between two objects
- More space expands
- More red shifted/ longer wavelength
How was CMB discovered?
- Accidentally by two Americans on a radio
- Noticed a noise constant from every direction
- Arno Penzias + Robert Wilson
What are the fist 3 stages for every star?
x3 stages
Nebula
Protostar
Main sequence star
What comes after a main sequence star of smaller mass?
- Red giant
- White dwarf
- Black dwarf
What comes after a main sequence star of larger mass?
- Red super-giant
- Supernova
- Neutron star or Blackhole
What is and how does a nebula become a protostar?
Nebula- cloud of gas and dust
gravity draws the cloud together causing rise in density and temperature and pressure
Protostar- Nuclear fusion begins where hydrogen is turned into helium generating energy
How does pressure change a protostar into a main sequence star?
- As pressure increases due to nuclear fusion
- thermal expansion occurs- pressure from hot gas
- Causes expansion as FORCE due to pressure is stronger than gravity
- Pressure then decreases and gravity causes the star to shrink slightly
- Constant imbalance but stable
How long is a star a main sequence star?
-For most of its life
- Our sun for 10 billion years
Why do stars become red giants/ supergiants?
- Core runs out of hydrogen
- Uses helium as its fuel to form carbon
What is a white dwarf and what does it become?
- Very small dense core
- Initially very hot but cools into
- A black dwarf (cold)
What happens to red giants?
- Unstable
- expels outer layers quickly
- Turns into a white dwarf
What happens to a red supergiant?
- After a few million years all helium is used up
- Starts to use carbon as its fuel
- Continuous until it builds up an iron core
- Explodes as the core succumbs to gravity and there is no fuel left (supernova)
What happens during a supernova and after?
- All elements heavier then iron are created and expelled into space
- smaller mass core becomes a neutron star
- Larger mass core collapses into a black hole
What did the invention of photography allow for astronomers?
-Ability to take photos of the universe that we are unable to see
-Clearer + easier to study
Why are telescopes placed outside the Earth’s atmosphere?
- Atmosphere absorbs radiation the telescopes needed to detect
- Away from the blurring effect of the atmosphere- clearer images
What did the invention of computers allow astronomers to do?
1960S create the first detailed model of supernova explosions
What did the invention of telescopes allow us to see?
Earth’s place in the heliocentric solar system
- Planets and asteroids
- Mountains and craters on the moon
