space🌚 Flashcards
what are moons
natural satellites which orbit planets
what is the solar system a part of
the milky way galaxy
what is a galaxy
a massive group of stars
how do stars form
- stars form from clouds of dust and gas (a nebula)
- gravity causes the cloud of dust and gas to collapse ( a protostar)
- as the dust particles move faster, the temperature rises to millions of degrees celsius
- if the temperature of the protostar gets high enough, then hydrogen nuclei join together to form helium, this is called nuclear fusion
- nuclear fusion releases a lot of energy
- There are two forces acting on a star :
- the force of gravity acts inwards and makes the star collapse
- the energy from nuclear fusion causes a force to act outwards on the star causing it to expand - The star is in equilibrium as these 2 forces are balanced
what is the main gas in a nebula
hydrogen
what galaxy is our solar system a part of
the milky way
what is the main gas in a nebula
hydrogen
describe the early lifecycle of stars
- stars begin life as a cloud of dust and gas which is a nebula
- gravity causes the cloud of dust and gas to collapse
- as the particles move faster, the temperature rises to millions of degrees C
( this early stager is called a protostar) - if temperature gets high enough then hydrogen nuclei join together using nuclear fission to form helium
(at this point, we have a main sequence star)
what happens to stars that are around the same size as our sun
- in a main sequence star, hydrogen fuse together to create helium
- at some stage, the hydrogen in the star begins to run out
- at this point, the outward force due to fusion energy is less than the inward force due to gravity
- this causes the star to collapse inwards
- this collapse causes the star’s temperature to increase
- the helium nuclei fuse together to make heavier elements
- the star expands to form a red giant
- at some point the red giant stops fusing helium, and at this point, the star shrinks and becomes a white dwarf
- because the white dwarf isnt carrying out fusion, it gradually cools down
- eventually, it stops releasing any energy and forms a black dwarf
what happens to stars that are bigger than our sun
- once these stars run out of hydrogen, they expand into a red super giant
- helium nuclei fuse together to produce heavier elements
- at some point, red super giant stops carrying out nuclear fusion
- at this stage the star explodes and this is called a supernova and elements from it are distributed throughout the universe
- after a supernova, the remains of a star can form a neutron star or a black hole
what elements can nuclear fusion make
any element lighter than iron, cannot be heavier than iron
where do elements that are heavier than iron come from
when a star explodes and becomes a supernova, its temperature is high enough to produce elements heavier than iron
what is a neutron star
one that consists of neutrons densely packed together
what is a black hole
one that has such a large gravity that even light cannot
what holds planets in their orbit
the force of gravity
what might the force of gravity lead to in circular orbits
a change in velocity, but not a change of speed
why does the speed not change for objects in circular orbit, but the velocity does
because velocity is the speed of an object in a given direction, since the direction is constantly changing, the velocity is constantly changing
what must happen if the speed of a satellite changes
the radius of the orbit must also change
what happens if the speed of a satellite increases and why
the radius decreases, this is because at a higher speed, the satellite needs a greater force of gravity to prevent it flying off into space
- by moving closer to earth, the gravitational force on the satellite is greater and the satellite remains in a stable orbit
what happens if a satellite is moving too quickly
the gravitational attraction between the Earth and the satellite is too weak to keep it in orbit. If this is the case, the satellite will move off into space. This occurs at speeds around or above 11,200 metres per second (m/s).
what would happen if a satellite is moving too slowly
the gravitational attraction will be too strong, and the satellite will fall towards the Earth. This occurs at speeds below 7600 m/s.
what is a stable orbit
one where the satellite is moving at a just right speed, and will travel along the right path without falling down or flying into space
what does a change in velocity result in
acceleration
when will an object accelerate if its moving in a circle
an object will accelerate if there is a resultant force on it, for objects moving in a circle, this force is called a centripetal force, which acts towards the middle of the circle
what provides the centripetal force needed to keep satellites in orbit
gravitational attraction
how does gravitational attraction link to distance
the closer the two objects are to each other, the stronger the force of gravity between them.
why do objects in small orbits travel faster than objects in larger orbits
If the gravitational force between two objects is greater, a greater acceleration will occur.
The greater the acceleration, the greater the change in velocity - this causes the object to move faster.
what happens during the main sequence phase of the star
- gravitational attraction tends to collapse the star
- radiation pressure from the fusion tends to expand the star
-forces caused by gravitational attraction and fusion energy are balanced
what fusion reaction takes place in a star
Two hydrogen nuclei fuse to produce a helium nucleus and a neutron.
what is red shift
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
- they shift to the red end of the spectra
why does red shift happen
- because light waves get stretched as they make their way to earth
- because of the space between the Earth and the galaxies expanding
how can we tell how fast a galaxy is moving away from the earth
The more red-shifted the light from a galaxy is, the faster the galaxy is moving away from Earth
what does the red shift provide evidence for
the big bang theory
what does the big bang theory suggest
that the universe began from a very small region that was extremely hot and dense, and it expanded into the universe we see today
what did the observations of supernovae prove
that the rate of expansion is increasing
what is dark mass and dark energy
matter and energy in the universe which we cannot detect
how can we tell that the universe is expanding
distance galaxies are moving faster than nearby ones
how do some scientists believe the universe began
from a very small region that was extremely hot and dense
