Topic 7: Astronomy Flashcards
(16 cards)
Explain how and why both the weight of any body and the
value of g differ between the surface of the Earth and the
surface of other bodies in space, including the Moon
Different bodies in space have different gravitational field strengths, meaning the value of g would differ
The weight of any body would differ too as mass stays the same no matter where you are but since gravitational field strength is changing, weight would also change
For example, the moon has a much weaker gravitational field strength so the value of g and weight would hence be less
Recall that our Solar System consists of
the Sun (our star), eight planets and their natural satellites (such as our Moon); dwarf planets; asteroids and comet
Describe how ideas about the structure of the Solar System
have changed over time
Geocentric model:
Everything rotates around the earth, each planet is circling around orbiting themselves
Heliocentric model:
Central star in the middle of the system which everything orbits around. No more circling/orbiting itself
Describe the orbits of moons, planets, comets and artificial
satellites
Planets orbit the Sun in nearly circular paths, while moons orbit planets in a similar fashion. Comets, on the other hand, follow highly elliptical orbits around the Sun. Artificial satellites can have various orbits, including circular and elliptical paths around planets however they are mostly circular
Explain for circular orbits how the force of gravity can lead to
changing velocity of a planet but unchanged speed
the force of gravity can be seen as a centripetal force so the planet is constantly moving at the same speed around the star. The velocity changes because velocity is speed in a stated direction and because direction is constantly changing velocity is also constantly changing
Explain how, for a stable orbit, the radius must change if
orbital speed changes (qualitative only)
The gravitational attraction between two objects decreases with distance. This means that the closer the two objects are to each other, the stronger the force of gravity between them. If the force between them is greater, a greater acceleration will occur.
The greater the acceleration, the greater the change in velocity - this causes the object to move faster. This means that objects in small orbits travel faster than objects in large orbits. In order to change orbital speed, an object must change the radius of its orbit at the same time, to maintain a stable orbit.
Compare the Steady State and Big Bang theories
Steady State:
First suggested in 1948
Universe has existed for as long as time
Universe expands due to matter entering the universe through white holes
Density is constant over time
This way new matter is constantly being created
Big Bang:
First suggested in 1920
Whole universe and matter started out as a tiny point of concentrated energy (extremely hot/dense)
Universe is expanding after the sudden explosion
Universe is still expanding - density becomes less over time
Describe evidence supporting the Big Bang theory, limited to
red-shift and the cosmic microwave background (CMB)
radiation
Red Shift:
The shifting of absorption lines in the spectra of stars towards
the red end of spectrum.
This is the evidence that the universe is expanding as galaxies
are moving away.
CMB radiation:
At the beginning of the Big Bang huge amounts of radiation (gamma rays) were released
As the universe is expanding, wavelength of the gamma rays decreased so it becomes low energy radiation - only detected as microwave radiation
Why is the Big Bang theory the currently accepted theory
as there is more evidence supporting the Big Bang theory than the Steady State theory, it is the currently accepted model for the origin of the Universe
Describe that if a wave source is moving relative to an
observer there will be a change in the _____ _______ and
_________
observed frequency
wavelength
Doppler effect: change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source.
The waves are squeezed or spread apart
What are the absorption lines in red shift
Chemical elements in the object which absorb specific wavelengths of light
How does red shift account for the steady state theory
The Steady State theory proposes that the universe has always existed in a state of continuous expansion and that matter is created
to maintain a constant density.
As the universe expands, galaxies move apart from each other, leading to redshift.
Redshift as evidence:
The expansion of space between galaxies causes the light from them to be redshifted.
What is the evolution of stars similar mass to the sun
Nebula - a cloud of dust and gas
Protostar - Due to gravitational attraction, the gas and dust clumps together. Gravitational potential energy is converted into thermal energy. The gas starts to glow forming a protostar.
Main sequence star - When fusion of hydrogen occurs inside the core. Outward pressure from fusion is balanced out by gravity which acts inwards
Red Giant - Without outward radiation pressure the core will collapse under gravity and become even hotter. Eventually the temperature will be high enough to cause the fusion of helium into heavier elements such as carbon and oxygen. The now greater outward radiation pressure will cause the outer layers to expand into a Red Giant.
Planetary nebula and white dwarf - A final collapse of the core occurs to form a very hot dense object about the size of the Earth called a white dwarf. The rest of the Sun is blown away to form a planetary nebula (from which a new star might form).
What is the evolution of stars higher mass to the sun
Nebula - a cloud of dust and gas
Protostar - Due to gravitational attraction, the gas and dust clumps together. Gravitational potential energy is converted into thermal energy. The gas starts to glow forming a protostar.
Main sequence star - When fusion of hydrogen occurs inside the core. Outward pressure from fusion is balanced out by gravity which acts inwards
Red Supergiants - Supergiants will also cause elements such as carbon and oxygen to undergo nuclear fusion to form even heavier elements such as silicon and iron.
Supernovae - When a red supergiant star causes iron in its core to undergo nuclear fusion, energy is absorbed. This slows the fusion process, decreasing pressure in the core and causing a great implosion. This rebounds and causes a cataclysmic event that can for a few days outshine a whole galaxy. This is called a supernova.
Neutron stars - The core left over from a supergiant star can be so massive that gravity causes electrons and protons to combine to form neutrons. This is a neutron star.
Black holes - The most massive stars collapse to form black holes. The gravity caused by black holes is so strong that nothing can escape its event horizon, including light.
Explain how the balance between thermal expansion and
gravity affects the life cycle of stars
The balance between thermal expansion (outward pressure from nuclear fusion) and gravity (inward pull) dictates the life cycle of stars. During the main sequence, these forces are balanced, creating a stable star. However, when nuclear fusion ceases, the balance is disrupted, leading to either collapse and expansion (red giant), or, in massive stars, a supernova and potentially a neutron star or black hole.
Describe how methods of observing the Universe have
changed over time including why some telescopes are located
outside the Earth’s atmosphere
Modern telescopes provide much more data than the telescopes used hundreds of years ago, this is because: They can detect more wavelengths/frequencies in the EM spectrum than just visible light. They can be positioned above the Earth’s atmosphere where less radiation is absorbed. They can detect weaker signals.
