Topic 7 - Astronomy Flashcards
Equation for weight (N)
weight = mass (kg) x gravity
Describe our solar system
- Sun lies at centre (helio-centric)
- 8 planets orbit the sun
- Natural satellites orbit the planets e.g. Moon for Earth
- Dwarf planets orbit the sun (including Pluto, Ceres)
- Asteroids and comets
Describe what planets are mad of and how they all fit into our solar system
- Small planets made of primarily rock, larger planets are primarily gas
- All planets orbit the Sun on the same plane and all 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, as gravitational field is so strong it attracts debris
Describe the ‘‘geocentric’’ model of our solar system
Earth was at the centre, planets, our moon, and the sun, all orbited the Earth
- Everything orbited in perfect circles
- With fixed background of stars
Describe ‘‘heliocentric’’ model of our solar system
- 600 years after ‘‘geocentric’’ model, heliocentric model was formed, with sun at centre
- evidence was Mars’ “retrograde motion”
- Earth orbits sun faster than mars, so we undertake it, so it appears to reverse its direction in the sky
- Galileo observed moons orbiting Jupiter showed not everything orbited the Earth
- Kepler showed that the planets orbited in ellipses, and not circles
What happens when a planet orbits the sun
- gravitational force causes planet to change direction constantly
- speed of planet is constant
- means the velocity is always changing
- the force causes the planet to accelerate without increasing its speed
What is a stable orbit
- the planet moves closer to the sun, so orbital radius decreases and gravitational attraction to sun increases
causes velocity to increase - so orbital speed of the planet increases
Describe red shift
- Light appears red shifted from galaxies that are at different distances away from the Earth
- When an object moves away from us, light is shifted to the red end of the spectrum, as its wavelengths get longer, so the object appears red
(blue shift is the opposite)
Evidence of the big bang
Red Shift
- shows universe is expanding.
Cosmic Microwave Background Radiation
- This radiation, as the universe expanded over time, would be stretched to become microwaves.
- background radiation is present wherever you point a telescope in the sky.
- proves the universe has cooled and expanded since
What is cosmic microwave background radiation
-the measure of the level of ionising radiation present in the environment
What is the steady state theory
- As universe expands, matter is being created so there is a constant density of matter in the universe.
- The red shift supports this theory
- suggests the observable universe is the same at any time and any place.
- But different stars were present at different eras of the universe, so shows universe has evolved and not stayed the same, so this cannot be correct.
- theory does not account for CMB.
Describe the life cycle of a star
- Dust and gas cloud is present in a galaxy
- Interstellar matter clump together to form clouds called nebulae.
- 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
- 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
- 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
describe the life cycle of a star (dying)
- the star runs out of gas to fuse
- means it is not in equilibrium, so it collapses
o If the star is massive - star will collapse, increasing the pressure + temperature of the core, so heavier elements can fuse. -when all fusion has happened, it’s too massive to be stable, so star collapses, rebounds on its centre and
produces a supernova
▪ What remains is either a neutron star or black hole
o If the star is normal-sized - same process happens, but less fusion occurs
▪ The star swells to produce a red giant star fusing heavier elements
▪ Once all reactions are over the star contracts and cools into a white dwarf
How has methods of observing the universe changed over time?
- Early refracting telescopes evolved to reflecting telescopes, which could be made larger and cheaper -refracting lenses are expensive and heavy
- Technological advances allowed other parts of EM spectrum to be measured and collected
Observing the universe- measuring rays
- to measure X-Rays, Gamma and UV telescopes have to be outside atmosphere, because earth’s atmosphere doesn’t allow these rays to reach the ground.
