Topic 7 - Astronomy Flashcards
Why does weight vary between bodies?
weight = mass x gravitational field strength
The greater the gravitational field strength, the greater the weight of an object. Same for mass.
Why does gravitational field strength vary between bodies?
Because they have different masses, radii (radiuses) and density
What does our solar system consist of?
-The sun as our star
-Eight planets
-The planets’ natural satellites (e.g. our Moon)
-Dwarf planets
-Asteroids
-Comets
State the names of the 8 planets in our solar system in terms of increasing distance from the sun
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Describe the initial model of the solar system
The initial model was geocentric, suggesting the earth was at the centre and orbited by the planets, our moon and the sun. Everything orbited in perfect circles with a fixed background of stars.
What enabled the geocentric model to be widely believed?
The only evidence was the naked eye which indicated that the sun, moon and planets moved across the sky in the same direction and motion every day
Describe the current model of the solar system
The current model is heliocentric, with the sun at the centre. Planets have their own moons. The earth rotates. Orbits are elliptical not spherical
Why has our view of the universe changed?
Evidence supported the heliocentric model.
-Telescopes allowed Galileo to observe that the moons of Jupiter rotate around Jupiter — indicating that not everything rotates around the earth. This debunked the geocentric model
Describe the orbits of moons, planets, comets and artificial satellites
-Planets follow an approximately circular orbit around the sun
-Satellites, including moons, follow an approximately circular orbit around planets
-Comets follow elliptical orbits around the sun
Explain for circular orbits how the force of gravity can lead to changing velocity of a planet but unchanged speed
When an object moves in a circle at a constant speed, its direction constantly changes — resulting in a change in velocity, and therefore accelerating. The centripetal force acts as a resultant force towards the middle of the circle. Gravitational attraction provides the centripetal force needed to keep planets and all types of satellite in orbit.
Explain how, for a stable orbit, the radius must change if orbital speed changes (qualitative only)
The gravitational attraction between 2 objects decreases with distance. The closer they are, the greater the force of gravity between them. If this force is greater, a greater acceleration will occur. The greater the acceleration, the greater the change in velocity. Therefore, objects in small orbits travel faster than objects in large orbits.
This means that, in order to change orbital speed, an object must change the radius of its orbit at the same time, to maintain a stable orbit.
Describe the Big Bang Theory
The Big Bang Theory states that the universe expanded from a very small dense point about 14 billion years ago
Describe the Steady State Theory
The Steady State theory says that the universe has always existed but is expanding and creating matter to counteract the loss of density.
It suggest the universe has no beginning. It also requires the continual formation of new matter.
Describe how the red shift is evidence for the Big Bang theory
As a star moves away from the earth wavelength increases and the frequency decreases — this is known as red shifting. In nearly all cases, the further away a galaxy is the more red shifted its light is, so the faster they are moving and the expansion is stretching out the light waves, shifting them towards the red of the EM spectrum.
This showcase of galaxies moving away from each other provides evidence for both the Big Bang and Steady State theories as both include an expanding universe.
Describe the Doppler effect
If a wave source is moving relative to an observer there will be a change in the observed frequency and wavelength.
This relates to the red shift as evidence for the expansion of the universe
Describe how cosmic microwave background radiation (CMBR) is evidence for the Big Bang Theory
CMBR radiation comes from all directions in space and has a temperature of about -270°C. It is suggested that this is the remains of the thermal energy from the Big Bang, spread thinly across the whole universe. It is believed that the short wavelengths of gamma radiation emitted in the initial explosion became stretched due to the expansion of space into longer wavelength microwaves.
This provides evidence that the universe began at one point and expanded, supporting the Big Bang theory.
What is the current belief about the origin of the universe and why?
The Big Bang theory is the currently accepted model for the origin of the universe because it has more evidence supporting it than the Steady State theory. This evidence includes CMBR and the red shift.
Describe a nebula and how it becomes a main sequence star
They begin as a nebula. This is a cloud of gas. The atoms are pulled towards each other by gravitational force and the temperature increases until the star becomes hot enough for nuclear fusion. This is a main sequence star.
Describe the relationship between the features of a main sequence star
The higher the brightness, the greater the temperature.
The greater the mass, the greater the temperature.
Describe how a main sequence star becomes a red giant
When all the hydrogen has been used up in the fusion process, larger nuclei begin to form and the star may to expand to become a red giant.
Describe how a red giant star becomes a white dwarf star
When all the nuclear reactions are over, a small star, around the mass of the sun, may begin to contract under the pull of gravity. It becomes a white dwarf which fades and changes colour as it cools.
Describe the evolution of stars with a mass larger than the sun when
These stars evolve from a main sequence star to a red super giant star (similar to a red giant).
It will then go on making nuclear reactions, getting hotter and expanding until it explodes as a supernova.
This throws hot gas into space.
The supernova will leave behind either a neutron star or a black hole. When a black hole is formed it allows nothing to escape.
How have methods of observing the universe changed over time?
Early refracting telescopes evolved to reflecting telescopes which could be made larger and cheaper (as refracting lenses are expensive and heavy).
Technological advances allowed other parts of the EM spectrum to also be measured and collected.
Why are some telescopes located outside the Earth’s atmosphere?
Observations can use any wavelength in the EM spectrum.
To measure X-rays, gamma and UV these telescopes need to be outside the atmosphere as the atmosphere does not allow these to reach the ground because it absorbs them. Light pollution can also make some images less clear.
