10 space Flashcards
What is transmitted by the earth’s atmosphere?
visible
Why are larger mirrors used on reflector telescopes?
brighter images (bigger mirror collects more light)
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
What are the three ways to measure distance in space?
Astronomical Unit (AU)
Astronomical Unit (AU)
the mean radius of the earth’s orbit (1.5e11m)
Astronomical unit use
to measure distances in our solar system
Light Year
the distance that light travels in a year (9.45e15m
Parsec
the distance when the parallax angle is 1 arcsecond (1/3600 degrees)
1 parsec in metres
3.09e16m
Trigonometric parallax uses
measure distances to nearby stars
Trigonometric parallax
The star is viewed from two positions at 6 month intervals
Trigonometric parallax as the angle decreases in size…
the object gets more distant
Apparent Magnitude letter
m
Apparent Magnitude
m
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 absorption lines on hydrogen)
Spectral class order
OBAFGKM
O
hottest spectral class
B
blue
A
blue-white
F
white
G
yellow-white
K
orange
M
coolest spectral class
Sun spectral Class
G
Hertzsprung Russel Diagram Y axis
Absolute magnitude
Hertzsprung Russel Diagram X Axis
Spectral class / Temperature (Hot to cool
Small Star Life Cycle
Stellar Nebula
Stellar Nebula/protostars
Cloud of hydrogen in space
Main sequence stars
hydrogen fuses to helium then helium fuses to heavier elements and the luminosity increases. Yellow Dwarf
Stellar remnants (for small stars)
The carbon core contracts until its only supported by electron pressure. When the excess gas/dust is lost
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 rotates 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
Doppler effect
the frequency of the wave is increased/reduced because an object is moving towards/away from a receiver
RedShift
when galaxies move away from 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 Hubble’s law
a direct correlation between the distance to a galaxy and its recessional velocity as determined by the red shift.
Hubble’s law
V = Hd
How to work out the age of the universe
1/ Hubble constant
History of the universe
the big bang (rapid inflation
Evidence for the big bang
hydrogen:helium ratio
How is the hydrogen:helium ratio 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 big bang
Steady state
an alternative universe theory suggesting 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
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
Critical/ flat universe
the universe’s density is perfect; it will expand forever at a decelerating rate.
Standard candle
a star with known luminosity
Cepheid variable star
a predictable standard candle (or supernova)
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)
Sun’s life cycle of a star (fusion based)
The Sun is fusing hydrogen into helium in its core. When hydrogen fusion ceases
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
if 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
What happens when a star cools?
it contracts
How to measure distances too big for standard candles
measure change in wavelength/frequency
Doppler shift
change in frequency/wavelength due to the relative motion of galaxy
What conclusions did Hubble reach
Recessional velocity ∝ galaxy distance
Critical density
Density is large enough to prevent the Universe expanding forever 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 Hubble’s constant
since the start of time
Why is it hard to predict the fate of the universe
because dark matter is undetectable
Dark matter
matter we can’t detect that exists in space
Dark matter examples
black holes
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
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)
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
Red giant/ super giant
truncated main sequence stars
