SP7 Astronomy Flashcards
Define weight
The force acting on an object due to gravitational attraction
What is the equation used to calculate weight?
weight = mass x gravitational field strength
How does the mass of a planet affect the weight of something on said planet?
The greater the mass of a planet = the greater its gravitational strength
The greater the mass of a planet = the greater its gravitational strength
Why is this true?
The more mass a planet has = a greater gravitational pull = higher the value of gravitational acceleration = greater value of g
What does the solar system consist of?
- the sun
- eight planets
- dwarf planets
- natural and artificial satellites
- asteroids and comets
What are the four gas giants?
Jupiter, Saturn, Uranus , Neptune
What are the four rocky planets?
Mercury, Venus, Earth, Mars
Why do larger planets have rings?
Their gravitational pull is so strong that it attracts debris
How long does light from the sun need to reach us here on Earth?
8 minutes
What was the geocentric model?
- model that put earth in the centre
- and the other planets + sun orbited earth
- everything orbited in perfect circles
- with a fixed background of stars
What is the heliocentric model?
Sun was at the centre of planets’ orbit, instead of the Earth
What was the evidence for the heliocentric model?
- mars being in retrograde
- Galileo observing Jupiters’s moons orbiting it
- Kepler showed that planets orbited in elipses instead of perfect circles
When a planet is orbiting the sun, its velocity is always changing. How is this possible?
- gravitational force causes planet to change direction constantly
- but speed of planet is constant
- velocity is always changing = accelerating without increasing its speed
- same goes for satellites around a planet
Why is it that closer planets have a faster orbital speed than gas giants?
- closer the planet = stronger the sun’s gravitational strength
- force increases
- therefore acceleration increases
- causing an increase in velocity
- therefore orbital speed is faster
Describe the orbits of all planets around the sun
- slightly elliptical
- orbit in the same plane
- travel the same direction around the sun
Describe the orbit of comets
- highly elliptical
- causes speed of comet to change
- not all comets orbit in the same field as planets + may not even be in the same direction
What are the two forces that stars are held together by?
Gravitational pressure and pressure caused by thermal expansion
What happens when the temperature of a star increases?
The star begins to expand because outward pressure will increase
What happens when the temperature of a star decreases?
Outward pressure decreases, star begins to shrink
Name the life cycle of solar mass stars
- nebulae
- protostar
- main sequence star
- red giant
- white dwarf
What is a nebula?
All stars form in giant clouds of hydrogen gas and dust called a nebula
Define protostar
- The force of gravity within a nebula pulls the particles closer together until it forms a hot ball of gas
- As the particles are pulled closer together the density of the protostar will increase
- This will result in more frequent collisions between the particles which causes the temperature to increase
Define main sequence star
- temperature and pressure of protostar increases as particles get pushed so close
- eventually, temperature and pressure gets so great that particles are able to fuse together
- fusion releases a large amount of energy that opposes the collapsing of the cloud due to gravity
- forming an equillibrium
Define red giant
- eventually, star runs out of gas to fuse, causing it to collapse
- collapse increases the pressure and temperature of the core allowing heavier elements to fuse
- as core shrinks, outer layer of star will expand and start to cool
