space physics Flashcards
What does our solar system contain?
- One star (the Sun)
- Eight planets
- Dwarf planets
- Natural satellites (the moons)
Describe the Sun in terms of its position in the solar system
- The sun lies at the centre of our solar system, it is heliocentric.
What orbits the Sun?
- The eight planets and the dwarf planets orbit around the Sun
What orbits the planets?
- Natural satellites (the moons) orbit planets
Define a planet
- Large objects that orbit a star
- Large enough so that their gravity is strong enough to have pulled in any nearby objects apart from their satellites
List the planes that orbit the Sun in order
- Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, (pluto)
Define a dwarf planet
- Planet-like objects that orbit stars, but don’t meet the rules of being a planet
Give an example of a natural satellite
- Not man-made
e.g. the moon
Define an artificial satellite
- Satellites that humans have built
- They generally orbit the Earth
- There are also asteroids and comets
What is our solar system a small part of?
- Our solar system is a small part of the Milky Way galaxy
Define the Milky Way galaxy
- A collection of billions of stars that are all held together by gravity
How was the sun formed?
- The Sun was formed from a cloud of dust and gas (nebula) pulled together by gravitational attraction
Describe the differences between the planets
- Smaller planets are made of primarily rock whereas larger planets are primarily gas
- Planets rotate at different speeds
- Some planets rotate in the opposite direction or on a skewed axis to the other planets - may be due to past collisions throwing its axis off balance
- Larger planets have rings - gravitational field is so strong it attracts debris
Describe the similarities between the planets
- All planets orbit the Sun on the same plane
- All planets rotate
What were the initial theories about the solar system?
- Initially, Earth was at the centre, the planets, our moon, and the sun, orbited the Earth
- “Geocentric” model
- Everything orbited in perfect circles
- With a fixed background of stars
When was the heliocentric model formed?
- 600 years after the geocentric model
What was the evidence for the heliocentric model?
- The main evidence being Mars’ “retrograde motion” - Earth orbits the Sun faster than Mars, so we undertake it (appears to reverse its direction in the sky)
- Galileo observing moons orbiting Jupiter showed not everything orbited the Earth
- Kepler showed that the planets orbited in ellipses, and not circle
- (HT only) for circular orbits, the force of gravity can lead to changing velocity but unchanged speed
*As the planet orbits the sun, the gravitational force causes the planet to change direction constantly (it moves in a circle around the sun)
* This means the velocity is always changing
* Hence the force causes the planet to accelerate without increasing its
speed
(HT only) for a stable orbit, the radius must change if the speed changes.
For a stable orbit: the radius must change if the speed changes
* If the planet moves closer to the sun, (i.e. its orbital radius decreases)
* The gravitational attraction to the sun increases (Force increases, and so does acceleration)
* So the orbital speed of the planet increases
Explain how, at the start of a star’s life cycle, the dust and gas drawn together by gravity causes fusion reactions
- Dust & gas cloud is present in a galaxy - the gravitational attraction between the gas/dust particles draws them together
- The cloud becomes more concentrated, as the particles get closer
- The temperature and pressure of the cloud increases as the particles get pushed so close together
- Eventually the pressure gets so great that the gas/dust particles are able to fuse together
Explain how fusion reactions lead to an equilibrium between the gravitational collapse of a star and the expansion of a star due to fusion energy
- Fusion occurs as the light (mainly hydrogen gas) nuclei fuse together to form helium nuclei
- This creates a large amount of energy
- This release opposes the collapsing of the cloud due to gravity
- So eventually an equilibrium forms, where the energy released due to fusion balances the pressure of gravitational collapse
This means a star has now formed, and it will stay like this for billions of
years
- Eventually the star runs out of gas to fuse
o This means it is not in equilibrium, so it collapses
Describe the life cycle of a massive star
- The star will collapse, increasing the pressure + temperature of the core,
meaning heavier elements can fuse. Once all the fusion has happened, it is
too massive to be stable, so the star collapses, rebounds on its centre and
produces a supernova - What remains is either a neutron star or black hole
Describe the life cycle of a normal-sized star (the Sun)
- The same process happens (as a massive star), less fusion occurs however (less fuel to fuse)
- The star collapses, and produces a planetary nebula
- A lower scale supernova
- A white dwarf remains
A star goes through a life cycle. The life cycle is determined by the size of the star.
What does fusion processes in stars produce?
- Fusion processes in stars produce all of the naturally occurring elements.
How are elements heavier than iron produced in a star?
- Elements heavier than iron are produced in a supernova
What happens when a massive star explodes (supernova)
- The explosion of a massive star (supernova) distributes the elements throughout the universe.
Explain how fusion processes lead to the formation of new elements
What does allows planets and satellites to maintain their circular orbits?
- Gravity provides the force that allows planets and satellites (both natural and artificial) to maintain their circular orbits.
Describe the similarities and distinctions between the planets, their moons, and artificial satellites
There is an observed increase in the wavelength of light from most distant galaxies. The further away the galaxies, the faster they are moving and the bigger the observed increase in wavelength. This effect is called red-shift.
What provides evidence for the expansion of the universe and supports the Big Bang theory?
- The observed red-shift provides evidence that space itself (the universe) is expanding and supports the Big Bang theory.
What does the Big Bang theory suggest?
- The Big Bang theory suggests that the universe began from a very small region that was extremely hot and dense
Since 1998 onwards, observations of supernovae suggest that distant galaxies are receding ever faster.
Students should be able to explain:
• qualitatively the red-shift of light from galaxies that are receding
explain that the change of each galaxy’s speed with distance is evidence of an expanding universe
Explain how scientists are able to use observations to arrive at theories such as the Big Bang theory
explain • that there is still much about the universe that is not understood, for example dark mass and dark energy.
Expalain the red shift
Light appears red shifted from galaxies which are moving away from Earth
- The change with distance of each galaxy’s speed is evidence of an expanding universe
- Imagine start of the big bang as an un-stretched balloon, with galaxies on the surface of the
balloon, and as the universe expands, the balloon expands
o The distance from the galaxies also expands
o So light from a galaxy has its wavelength “red-shifted” as it appears to move away
from us
o As wavelength appears to get larger (more in the red-end of the visible spectrum)
o Frequency appears to decrease, as each time a wavelength is emitted, the source
(galaxy) is further away
How does the Red Shift give evidence for the Big Bang?
- This shows universe is expanding
- So initially, it must have been formed from a single point
How does Cosmic Microwave Background radiation give evidence for the Big Bang?
- CMB
o Cosmic Microwave Background radiation
o When the universe was very young, everything, the first stars and rock, would be
very hot, and should have emitted lots of short-wavelength radiation
o This radiation, as the universe expanded over time, would have been stretched to
become microwaves
o This background radiation is present wherever you point a telescope in the sky
o 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
There is much about the universe that is not understood, for example dark mass and dark energy
