Topic 7: Astronomy Flashcards
7.1 Explain how and why the weight of any body and the value of g differ between the surface of Earth and the surface of other bodies in space, such as the Moon?
weight is the force of gravity acting on you, so if g changes, weight does too.
the gravitational field strength on the surface of a body (such as a planet or moon) depends on the mass of the body and the distance from its centre to its surface. the greater its mass and the smaller its radius, the greater its surface gravity.
7.2 what does our solar system consist of?
the Sun (our star), eight planets and their natural satellites (such as our Moon), dwarf planets, asteroids, and comets
7.3 what is the order of the planets in terms of distance from the Sun?
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
(My Very Easy Method Just Speeds Up Naming Planets)
7.4 describe how the ideas about the strcture of the solar system have chnaged over time
Geocentric Model - Earth was at the centre of the Solar System and the Sun and Moon orbited the Earth
Heliocentric Model - The Sun was at the centre of the Solar System and the Earth orbited it.
7.5 describe the orbits of moons, planets, comets and artificial satellites
moons: almost circular orbits
planets: ellipse orbit
comets: highly elliptical
artificial satellites: circular orbits
7.6 why do satellites with circular orbits have constant speed but constantly changing velocity?
as the planets orbit the Sun (or the Moon orbits the Earth), the gravitational force causes the planet to change direction constantly (because it is moving in a circle around the Sun), but the speed of the planet is constant. this means the velocity is all ways changing, hence the force causes the planet to accelerate without increasing its speed.
7.7 if orbital speed changes, how must the radius of the orbit change to keep it stable?
the gravitational force on a satellite in a low orbit is greater than that on a satellite in a high orbit.
the satellite in the low orbit has to be moving much faster to stay in its orbit.
if it slows down it will fall towards the Earth.
it gains speed as it falls, until it is moving fast enough to stay in a new, lower orbit.
if it goes low enough to encounter to the top of the atmosphere, contact with the air will slow it down and it will eventually fall to Earth.
7.8 what is the difference between the Steady State and Big Bang theories?
the Big Bang theory says that the whole Universe and all the matter in it started out as a tiny point of concentrated energy about 13.5 billion years ago. the Universe expanded from this point and is still expanding. as the Universe expanded, gravity caused matter to clump together to form stars.
whereas
the Steady State theory, says that the Universe has always existed and is expanding. new matter is continuously created within the Universe as it expands.
7.9 what evidence is there to support the Big Bang Theory?
red shift and cosmic microwave background radiation (CMB) support the Big Bang theory.
red shift shows that the universe is expanding, which suggests that it formed from a single point.
when the universe was very young, everything, the first stars and rock, were very hot, and should have emitted lots of short-wavelength radiation.
this radiation, as the universe expanded over time, would have been stretched to become microwaves.
this background radiation is present wherever you point a telescope in the sky, which proves that the hot young universe has cooled and expanded since.
as the Big Bang accounts for all the experimental evidence, it is the most accepted model currently.
7.10 what is the currently accepted model for the origin of the Universe, and why?
the Big Bang Theory, because there is more supporting evidence
7.11 if a wave source is moving relative to an observer, what will change?
the observed frequency and wavelength
7.12 how does the red-shift in light differ from different galaxies at different distances away from the Earth?
the further away they are, the more red-shift there is
7.13 how does red-shift provide evidence for the Universe expendaning?
the light from a distant galaxy shows red-shift if it is moving away from Earth. the movement of the source of light ‘stretches’ the wavelengths and so the pattern of lines had shifted towards the red end of the visible spectrum.
in the 1920s, Edwin Hubble investigated how far the pattern of lines was shifted for around fifty galaxies in comparison to the Sun. he discovered that they were almost all red-shifted and concluded that these galaxies were moving away from us. we interpret this relationship to mean that the Universe is expanding.
7.14 how do both the Steady State and Big Bang theories account for the red-shift of galaxies?
red-shift shows that the Universe is expanding. someone that believes that the Steady State theory would say that this is because the Universe is constantly expanding and creating new matter, whereas someone that believes in the Big Bang theory would say that this is because things are still moving because of the Big Bang.
how did the discovery of CMB radiation lead to the Big Bang theory becoming the currently accepted model?
- two radio astronomers who were building a radio telescope detected microwave signals coming from all over the sky.
- at first, they thought these were caused by a fault in their equipment, but eventually they realised that this was the radiation predicted by the Big Bang theory.
- the Big Bang theory says that huge amounts of radiation were released at the beginning of the Universe.
- because the Universe is expanding, the wavelength of this radiation has increased and so now it is only detectable as microwave radiation.
- it is called cosmic microwave background (CMB) radiation.
