space Flashcards
luminosity
rate of light energy released (power)
intensity
power per unit area (flux)
1 AU
distance from earth to sun, 1.5x10^11m
trigonometric parallax
parallax is the apparent change in position of a nearer star in comparison to distant stars, as a result of earths orbit around the sun. the property is measured by the angle of parallax. you can find the angle of parallax by measuring the angle to a star and seeing how this angle changes as the earth changes position. the greater the parallax angle, the closer the star to earth
parsec
distance when the parallax angle is 1 arc second (1/3600 degrees)
standard candle
object of known luminosity, astronomical distances can be found using them. done by measuring the intensity detected from the light source on Earth and using the inverse square law equation
hertzprung-russel diagram
starts belong to different spectral classes depending on their temperature
spectral classes from hottest to coldest
OBAFGKM
life cycle of stars( <1.4 solar masses)
nebula, protostar, mainsequence, red giant, white dwarf and blackdwarf
what does the hertzprung-russel diagram show
the stellar luminosity of a star against its temperature. by looking at the position of a star on the HR diagram, you will likely be able to tell which spectral class it belongs to.
(it goes from hot to cold left to right)
life cycle of stars (between 1.4 and 3 solar masses)
nebula, protostar, mainsequence, red giant, supernova and neutron star
life cycle of stars (>3 solar masses)
nebula, protostar, mainsequence, red supergiant, supernova and blackhole
protostar formation
-clouds of gas and dust have fragments of varying masses that clump together under gravity
-the irregular champs rotate and gravity/conservation of angular momentum spins them inwards to form a denser centre- a protostar
main sequence formation
-the inwards force of gravity and the outwards force due to fusion are in equilibrium-the star is stable
-hydrogen nuclei are fused into helium
-the greater the mass of the star, the shorter its main sequence period because it uses fuel more quickly
red giang formation
-once the hydrogen runs out, the temperature of the core increases and begins fusing helium nuclei into heavier elements (carbon, oxygen and beryllium)
-the outer layers of the star expand and start to cool
white dwarf formation
-when a red giant has used up all of its fuel, fusion stops and the core contracts as gravity is now greater than the outwards force
-the core becomes very dense
-it will eventually cool and become a black dwarf
red supergiant formation
when a high mass star runs out of hydrogen nuclei, the same process for a red giant occurs but at a larger scale
supernova formation
-when all fuel runs out, fusing stops and the core collapses inwards very suddenly and becomes rigid (as the matter can no longer be forced any closer together)
-the outer layers of the star fall inwards and rebound off of the core, launching them out into space in a shockwave
-as the shockwave passes through surrounding material, elements heavier than iron are fused and flung into outer space
-the remaining core depends on the mass of the star
neutron star formation
-when the core of a large star collapses, gravity is so strong that it forces protons and electrons together to form neutrons
black hole formation
-when the core of a giant star collapses, the neutrons are unable to withstand gravity forcing them together
-the gravitational pull is so strong light cannot escape
how can the life cycle of a star be observed using an HR diagram
1)begins as a protostar which gradually heats upon, moving to the left of the diagram. once it reaches temperatures to allow fusing to occur, it becomes a main sequence star
2)once the main sequence star uses up all its fuel, it will move to the right of the HR diagram as it becomes a red giant. It is cooler and brighter than a main sequence star
3)once the red giant uses up all of its fuel, it will eject its outer layers and will dive down to the left of the diagram as it becomes a white dwarf. it is hotter and dimmer than a main sequence star
the Doppler effect
the compression or spreading out of waves that are emitted or reflected by a moving source. as the source is moving, the wavelengths infant are compressed and the wavelengths behind are spread out.
red shift
the Doppler effect causes the line spectra of different objects to be shifted either towards the blue end of the visible light spectrum when moving towards Earth, or to the red end when moving away from earth.
red shift equation
redshift (z)=∆λ/ λ=∆f/f=v/c
this only works when v is much smaller than c as the formula was derived without taking into account relativistic speeds
red shift as evidence for the expanding universe
as different objects are red-shifted. the more distant the object, the greater its redshift.
Hubbles law
a galaxies recessional velocity is directly proportional to its distance from the Earth. therefore the universe is expanding from a common point
Hubbles law equation
v=Hod
d=distance from earth
v=recessional velocity
Ho=hubbles constant
the age and ultimate fate of the universe
the redshift of distant objects shows that they are moving away from us suggesting that the universe is expanding. it would be reasonable to assume that the universe began from one point- a singularity that was infinitely small and hot. its suggested that a huge explosion happened at this spot.
why is the age of the universe found by using hubbies constant not accurate
you ca rearrange the equation to fund that 1/Ho=t. however the value go Ho varies quite a bit depending on the method used to find it. therefore there is no exact known value for the age of the universe
dark matter
by considering centripetal force exerted on stars in the outer orbits of the galaxy, you’d expect them to travel slower than stars towards the galaxy centre. however this is not the case, as all the stars in the galaxy tend to travel at the same speed regardless of their distance to the centre of the galaxy.
this suggests that stars have a larger mass than they appear to, which allows them to travel at the speed that they are. this extra mass is believed to be caused by dark matter, which is yet to be detected as it does not emit or interact with light
why is the universe expansion accelerating
if the expansion of the universe was slowing down, more distant objects would be observed to be receding more quickly, since the expansion was faster in the past. objects would also be brighter than expected as they would be closer. however a certain type of supernovae have been seen to be dimmer than they were expected to be, which means they are more distant than Hubble’s law predicted
