Topic 10 -Space Flashcards
what is transmitted by the earths atmosphere?
visible
microwave
some radio
Why are larger mirros used on reflector telescopes?
- brighter images (bigger mirror collects more light)
- Better Resolution (Light spreads out less through a bigger hole)
radio telescope
a type of reflector telescope that is very large because radio waves have a large wavelength
Where must optical observatories be placed?
- Where there is little light pollution
- where the sky is clear
what are the three ways to measure distance in space?
- Astronomical Unit (AU)
- Light Year
- Parsec
Astronomical Unit (AU)
- the mean radius of the earths orbit (1.5e11m)
Astronomical unit use
to measure distances in out solar system
Light Year
the distance that light travels in a year (9.45e15m, using s = vt)
Parsec
the distance when the paralax angle is 1 arcsecond (1/3600degrees)
1 parsec in metres
3.09e16m
Trignometric parallax uses
measure distances to nearby stars
trigonometric parallax
The star is viewed from two positions at 6 month intervals
The change in angular position of the star against background of fixed stars
is measured
Trigonometry is used to calculate the distance to the star
The diameter/radius of the Earth’s orbit about the Sun must be known
Trigonometric parallax as the angle decreases in size…
the object gets more distant
Apparent Magnitude letter
m
Apparent Magnitude, m
how bright the star appears to someone on earth.
The smaller the number the brighter the star
Absolute Magnitude letter
M
Absolute Magnitude
how bright a star would appear if it were at a distance of 10pc from the observer
magnitude distance equation
m - M = 5log(d/10)
Wiens Law
a relationship between the peak wavelength of the spectrum and the temperature of the black body
wiens law equation
λmax T = 0.0029
spectral class
represents the temperature of a star (related to the absorbtion lines on hydrogen)
Spectral class order
OBAFGKM
O
hottest spectral class, blue, 25 000 - 50 000 K
B
blue, 11 000 - 25 000 K
A
blue-white, 7500 - 11 000 K
F
white, 6000 - 7500 K
G
yellow-white, 5000-6000K
K
orange, 3500-5000K
M
coolest spectral class, red, <3500K
Sun spectral Class
G
Hertzsprung Russel Diagram Y axis
Absolute magntitude
Hetzsprung Russel Diagram X Axis
Spectral class / Temperature (Hot to cool, logarithmic)
Small Star Life Cycle
- Stella Nebula
- protostar
- yellow dwarf
- red giant
- planetary nebula
- white dwarf
- black dwarf
Stellar Nebula/protostars
Cloud of hydrogen in space, protostars form when there is enough pressure for fusion.
Main sequence stars
hydrogen fuses to helium then helium fuses to heavier elements and the luminosity increases.
Yellow Dwarf, Blue giant, Red giant, Red super giant
Stellar remnants (for small stars)
The carbon core contracts until its only supported by electron pressure.
When the excess gas/dust is lost a white dwarf is left which will eventually cool and fade to a black dwarf.
Stellar remnants (for large stars)
the star collapses.
If the collapse of the core can be stopped by neutron pressure the star becomes a neutron star which rapidly toates and sends out pulsars.
Else if the neutron pressure cannot withstand gravity it collapses into a black hole.
Life cycle of a large star
- stellar nebula
- proto star
- blue super giant
- red super giant
- black hole or neutron star
Doppler effect
the frequency of the wave is increased/reduced because an object is moving towards/away from a reciever
RedShift
when galaxies move away us
BlueShift
when galaxies move towards us
How can you tell if redshift/blueshift is occurring?
the lines of the absorption spectra have shifted. All absorption spectra should be similar as the universe is mostly made from hydrogen/helium
redshift equation
change in wavelength / original wavelength = object speed / wave speed = cosmological redshift
What is hubbles law
a direct correlation between the distance to a galaxy and its recessional velocity as determined by the red shift.
hubbles law
V = Hd V = recessional velocity H = hubble constant d = distance
How to work out the age of the universe
1/ hubble constant
History of the universe
- the big band (rapid inflation, nothing but energy)
- fundamental particle were formed (electrons, quarks)
- Quarks formed protons and neutrons
- hydrogen atoms were made
- after millions of years the first stars formed
- after 8 billion years the solar system formed
Evidence for the big bang
- hydrogen:helium ration
- CMBR
- redshift/ expanding universe
How is the hydrogen:helium ration evidence for the big bang
neutrons are not stable so they decay. The ratio of hydrogen to helium matches the ratio of protons to neutrons.
Cosmic Microwave background
microwaves coming from every point in the sky is energy left over from the bigbang
Steady state
an alternative universe theory suggesting the the universe has always been as it is. The evidence suggests that it is wrong.
How is the accelerating expansion of the universe explained
dark matter and dark energy
What are theories on how the universe can end
- open
- closed
- critical /flat
The big crunch
closed universe theory. If the universe is too dense gravity halts the expansion and the universe eventually collapses
The big freeze/ the big rip/ heat death
Open universe theory. If the universe is not dense enough the universe will expand forever.
Critical/ flat universe.
the universes density if perfect it will exapnd forever at a decelerating rate.
Standard candle
a star with known luminosity
cepheid variable star
a predictable standard candle (or supernavae)
Uses of standard candles
to measure extremely long distances that can’t be measured with trigonometric parallax
how can intensity and luminosity be used to measure distance?
I = L / (4πd^2)
inverse square law
suns life cycle of a star (fusion based)
- The Sun is fusing hydrogen into helium in its core.
- When hydrogen fusion ceases the core of the Sun cools and collapses.
- The Sun expands and becomes a red giant
- The core becomes hot enough for helium fusion to begin in the core
- Helium begins to run out and the core collapses again
- The outer layers of the sun are ejected out into space
- The temperature doesn’t rise enough for further fusion to begin so The core/Sun becomes a (white) dwarf star
standard candle
a stellar object with known luminosity
How are standard candles used
the standard candles flux/intensity is measured. Use the inverse square law I = L/4πd^2 to calculate the distance.
why isn’t trigonometric parallax good for long distances
is the star is too distant the angle it moves by is too small so the uncertainty is too big
how do astronomers know white dwarfs are small?
White dwarf stars have:
- high temperature T
- low luminosity L
L = σAT^4 means that the surface area is small
what happens when a star cools
it contracts
how to measure distances too big for standard candles
- measure change in wavelength/frequency
- deatermine relative velocity using redshift velocity
- apply hubbles law v = Hd
doppler shift
change in frequency/wavelength due to the relative motion of galaxy
what conclusions did hubble reach
- Recessional velocity ∝ galaxy distance
- Red shift due to a galaxy moving away from Earth/observer
- Deduction of the expanding Universe
critical density
Density is large enough to prevent Universe expanding for ever but not too big to cause a collapse/contraction of the Universe
hubble constant
1.8e-18
unit of hubble constant
s^-1
assumptions when calculating the age of the universe through hubbles constant
- since the start of time
- galaxies travelling at constant speed
why is it hard to predict the fate of the universe
the it matter which is undetectable (dark matter) which effects the mass and density of the universe
dark matter
matter we can’t detect that exists in space
dark matter examples
black holes, neutrinos, subatomic particles
dark energy
theoretical energy that opposes gravity in space causing the universe expansion to accelerate
horizontal axis of a HR diagram
surface temperature of star / spectral class
How is the velocity of a galaxy determined
- Measure wavelength of light from the galaxy
- Compare it to the wavelength for a source on the Earth
- Shift in line spectra due to the doppler effect
- v/c = change in wavelength/ wavelength of source on earth
why is it so hard to predict the fate of the universe
- Due to the difficulty in making accurate measurements of distances to galaxies (Hubble constant has a large uncertainty)
- Because of the existence dark matter changes the mass/density
- Values of the average density/mass of the universe have a large uncertainty
- Dark energy makes it hard to predict how gravity will determine the ultimate fate
why is high temperature required in fusion
to overcome the electrostatic force of repulsion
why is high density needed in fusion
to keep a high collision rate
why do elements heavier than iron not fuse
Iron is the most stable element (peak of the binding energy curve). If a heavier element than iron was to fuse the binding energy per nucleon would decrease making it less stable AND THE REACTION WOULD REQUIRE AN ENERGY INPUT
red giant/ super giant
truncated main sequence stars
