astrophysics Flashcards
what is the universe + galazies
the universe is a large collection of billions of galaxies
* a galaxy is a large collection of billions of stars
* our solar system is in the Milky Way galaxy
relations between planets and gravitational field
- Planets have strong gravitational fields
Hence, they attract nearby masses with a strong gravitational force - Because of weight (The force acting on an object due to gravitational attraction) :
Objects stay firmly on the ground
Objects will always fall to the ground
Satellites are kept in orbit
The greater the mass of the planet then the greater its gravitational field strength
A higher gravitational field strength means a larger attractive force towards the centre of that planet or moon
The moon has less mass than the Earth, and so its gravitational field strength is
lower; supermassive black holes have the greatest mass and so the greatest g value
what the gravitational field forces does
The gravitational force causes moons to orbit planets,
artificial satellites to orbit the Earth, planets and comets to
orbit the Sun
why
planets orbit
- A smaller body or object will orbit a larger body
eg, a planet orbiting a Sun
gravitational force exerted by the larger body on the orbiting object is always attractive = so sun orbit planets
planets have a strong gravitation field which is attracted to a strong gravitational force of nearby masses
sun has strong g field which attracts planets with gf and keeps them in orbt
Therefore, the gravitational force always acts towards the centre of the larger body
orbit of planets
- slightly elliptical
- They all orbit in the same plane
- They all travel the same direction around the Sun
- planet closest to the Sun has the greatest speed and furthest travelts the slowest
orbit of moons
- circular orbit
- orbit at a constant speed
closer to the moon - shorter time taken to orbit
further to the moon - longer time taken to orbit
orbits of commets
elliptical - the speed of the comets to change as their distance from the Sun changes
- Not all comets orbit in the same plane as the planets
- As the comet approaches the sun, its speed increases
As it moves further away from the sun, its speed decreases
stars colour and temp
red is coolest
blue is hottestt
describe the evolution of stars of solar mass star
Stars form from a giant hydrogen gas and dust cloud called a nebula
* Gravitational attraction within the nebula pulls the gas and dust together – it
becomes denser and its temperature increases, forming a protostar
* Eventually the protostar is so hot and so dense that nuclear fusion begins (hydrogen
is fused to form helium) and the star enters the main sequence phase
* The temperature/colour of the main sequence star depends on its mass
* The main sequence phase ends when the star runs out of hydrogen, the core
shrinks, heats up, and starts a new series of fusion reactions producing heavier
elements; for stars with a similar mass to our Sun, the outer part of the star cools
and swells, to form a red giant
* Eventually fusion reactions finish and the core collapses, to form a white dwarf
evolutions of largers mass stars
High mass stars form in the same way - from a giant hydrogen gas and dust cloud
called a nebula, which collapses due to gravitational attraction – it becomes denser
and its temperature increases, forming a protostar
* Eventually the protostar is so hot and so dense that nuclear fusion begins (hydrogen
is fused to form helium) and the star enters the main sequence phase, but with more
mass the surface temperature is higher and the star is shorter lived
* The main sequence phase ends when the star runs out of hydrogen, the core
shrinks, heats up, and starts a new series of fusion reactions producing heavier
elements; for stars with a much greater mass to our Sun, the outer part of the star
cools and swells, forming a red supergiant
* Eventually fusion reactions finish, the core collapses during a supernova to form
either a neutron star, or, for the very high mass stars, a black hole
what disgramms are used
HERTZSPRUG RUSSLE DIAGRAMS
what is red shit and doppler effect
If the galaxy is moving away from an observer, then there is a decrease in the frequency and an increase in the wavelength of the wave, causing a red shift
describe the red-shift in light received from galaxies at different distances away
from the Earth
The red shift of galaxies is directly proportional to distance:
- If you double the distance to a galaxy its red shift is twice as large, indicating that it is moving away from us at twice the velocity:
why red shift is good evidence for BBT
This is because light waves are stretched by the expansion of the universe so the wavelength increases (or frequency decreases)
This indicates that the galaxies are moving away from us
This shows that the greater the distance to the galaxy, the greater the redshift
This means that the further away a galaxy is, the faster it is moving away from the Earth
why CBM waves is good evidence for BBT
13.9 billion years ago at the Big Bang the radiation produced took the form of
gamma waves showing that the universe was significantly hotter, but as the universe
has expanded and cooled the wavelength has progressively increased from gamma to
microwaves
