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