Unit 1.6 - Using radiation to investigate stars Flashcards
What do stars constantly emit?
A continuous spectrum of radiation
Where does the continuous spectrum of radiation from a star come from?
The dense gas of the surface of the star
Describe the atmosphere of the star’s atmosphere
Tenuous - the star’s atmosphere is a lot less dense than the gases forming in the surface
What do gases in the star’s atmospheres do?
Absorb certain wavelengths of light
What’s responsible for certain wavelengths of light being absorbed?
Atoms in the gases of the stars atmosphere
What causes absorption lines on the line absorption spectrum?
Atoms in the gases of the star’s atmosphere absorbing certain wavelengths of light
At what end of the electromagnetic spectrum is the wavelength shortest?
The red, gamma end
What’s the phrase for the unaffected spectrum of light emitted from stars?
Continuous spectrum
What does our brains interpret as white?
A mixture of colours from the continuous spectrum
What do you call the spectrum with the black lines?
Line absorption spectrum
What do the lines on the line absorption spectrum represent?
Certain wavelengths of light bring absorbed by gases in the stars atmosphere
What would the black line on a line absorption spectrum show on a graph?
A dip
What does a dip in a graph/a black line on the line absorption spectrum mean in terms of electrons?
Less of them
What’s the phrase for the line absorption spectrum from our sun?
Fraunhofer spectrum
What is wavelength measured in?
nm
Black bodies
Bodies which absorb all the electromagnetic radiation that falls upon it
What can no other bodies compare to black bodies with?
No body is a better emitter of radiation at any wavelength than a black body
What are good approximations of black bodies? Why?
Stars as they’re perfect “emitters” of electromagnetic radiation
What does the intensity of radiation emitted from a black body vary with?
The wavelength
What does wavelength vary for black bodies?
The intensity of the radiation emitted
What does a higher temperature mean for a black body curve on a graph?
-Higher peak intensity
-Lower peak intensity wavelength (shifted to the left)
What colour would hotter stars appear?
Blue
What would a lower temperature show on a black body graph?
A longer “flat” section before the curve “lifts off”
What do you call the curves on the black
body graphs?
Black body curves
What goes along the x and y axes on a black body graph?
x - wavelength
y - spectral intensity
What does Wien’s displacement law state?
The wavelength of peak emission from a black body is inversely proportional to the absolute (kelvin) temperature of the body
What does ŷ(upside down)max mean in Wien’s displacement law?
Wavelength of peak emission (m)
What does T mean in Wien’s displacement law?
Absolute temperature (K)
What does W mean in Wien’s displacement law?
The Wien constant
How do you figure out the temperature in Kelvins from °C?
Whatever it is in °C, plus 273.15
When is the energy of particles in a body the lowest it can be?
At 0K (-273.15°C)
What happens at 0k (-273.15°C)?
The energy of particles in a body is the lowest it can be
What did Stefan’s law state?
The total electromagnetic radiation energy emitted per unit time by a black body is given by…(the formula)
What does the P stand for in Stefan’s law? (+units)
Power (W)
What does the A stand fit in Stefan’s law? (+units)
Surface area of the black body (m2)
What does the o stand for in Stefan’s law?
The Stefan constant
What does the T stand for in Stefan’s law? (+units)?
Absolute temperature (K)
Luminosity of a star
The total energy it emits per unit time in the form of electromagnetic radiation
What’s luminosity measured in? What does this mean?
Watts
Luminosity = power
What does the fact that luminosity is power mean?
We can use Stefan’s law to calculate it
What does the inverse square law state? Why is this?
Less energy strikes each square metre of a surface per second as the distance from a light source increases
- Spread out over a larger “surface area”
Intensity
The amount of light energy striking each metre square per second
Intensity formula
I = P
—
4(pi)R2(little 2)
What does I stand for in the intensity formula (+units)?
Intensity of the radiation (Wm-2)
What does the P stand for in the intensity formula (+units)?
Total power (luminosity) from the star (W)
What does the R stand for in the intensity formula (+units)?
Distance from the star (m)
What does the 4piR2 represent in the intensity formula?
The surface area of an “imaginary” sphere radius of R
Multi wavelength astronomy
Studying stars by observing areas outside the visible light spectrum gives information on processes that took place
What’s an example of multi wavelength astronomy revealing something big?
Observing the microwave region of the spectrum revealed cosmic microwave background radiation (CMBR)
What does multi wavelength astronomy require and why?
Different telescopes that are sensitive to different wavelengths in the electromagnetic spectrum in order to get information on processes that took place
Why are colours in astronomy considered “false colours”? What’s the exception?
They’re used as an “intensity code”, not as actual colours
Visible light is an exception
What type of telescope do we use to observe visible light?
An optical telescope
List the types of electromagnetic radiation on the E-M spectrum in order of wavelength, starting from the longest wavelength
Radio
Micro
Infrared
Visible
Ultra violet
X-ray
Gamma
What range of wavelength are we able to see?
700nm-400nm
What does the electromagnetic spectrum show (+units)?
Wavelength (m) and Frequency (Hz)
Wave speed formula
c = y(upside down)f
What does c stand for in the wave speed formula (+units)?
Wave speed (m/s)
What does the upside down y stand for in the wave speed formula (+units)?
Wavelength (m)
What does f stand for in the wave speed formula (+units)?
Frequency (Hz)
What does energy do to an electron?
Excited electrons to lift them up the states
What excites electrons to lift them up the states?
Energy
What are the different states an electron travels up?
Infinity level
(etc)
3rd excited state
2nd excited state
1st excited state
Ground state
What happens when the electron reaches the infinity state?
It leaves the atom to become an ion
What happens to the excitement states as they increase?
Get closer
What does the gap between each excitement state of an electron represent?
A quantum - a quantity of energy proportional to the frequency of radiation it represents
What happens when a wavelength corresponds to an exact quantum?
When it corresponds to this exact energy jump, the photon disappears, the electron jumps an energy state and the photon randomly reappears
What does a black line represent on the line absorption spectrum in terms of electrons?
Less there
What does shorter wavelength mean in terms of energy?
More energy
What does more energy do for the electrons in the excitement states?
Higher jumps = more blue
What does the line absorption spectrum allow us to do?
Recognise gases in the stars’ atmospheres (look for oxygen - a sign of life!)
What’s the formula for the energy of a photon?
E = hc
—
y(upside down)
What does the E stand for in the energy of a photon formula (+unit)?
Energy (J)
What does the h stand for in the energy of a photon formula?
The Planck constant
What does the c stand for in the energy of a photon formula?
Speed of light in vacuo (on data booklet)
What does the upside down y stand for in the energy of a photon formula (+units)?
Wavelength (m)
Where does the Earth’s intensity of radiation peak? What does this mean?
Infrared- we can’t see at night, only with infrared glasses
Which law states that the wavelength of peak emission from a black body is inversely proportional to the absolute temperature of the body?
Wien’s displacement law
Which law shows us the total electromagnetic energy emitted per unit time by a black body?
Stefan’s law
Which law tells us that less energy strikes each square metre of a surface per second as the distance from a light source increases?
The inverse square law
What do we need to ensure when drawing a black body curve?
-Go through the origin (0)
-Don’t hit the x axis
-Show clearly where it peaks at (label it)
-Sharply up, gently down
+careful when converting between m and nm for wavelength!
Which has the most dense atmosphere? The star’s surface or its atmosphere?
Surface
What colour is a hotter star and why?
Blue as it peaks in ultra violet
What colour is a colder star and why?
Red as it peaks in infared
How many metres are in a nano metre?
1x10-9
What happens to the area when you double the distance (inverse square law)?
x4
What do you look at on the electromagnetic spectrum to figure out where a wavelength lies?
Wavelength
Radio wave wavelength
10^3
Microwave wavelength
10^-2
infrared wavelength
10^-5
Visible wavelength
.5x10^-6
ultra violet wavelength
10^-8
X-rays wavelength
10^-10
Gamma wavelength
10^-12
What shows us the total energy of a black body?
Area under the curve
Explain the formation of dark bonds on the line absorption spectrum
-Continuous spectrum from the core of the star passes through its cooler atmosphere
-Certain photons will be equal to the energy level gaps in the atoms of the atmosphere
-These photons are absorbed by the electrons in the lower states
-Excited electrons
-Fall back down
-Release identical photon - not necessarily in the original direction
-Intensity (brightness) of colours is reduced
Gamma rays characteristic temperature
More than 10^8 k
X-rays characteristic temperature
10^6 - 10^8 k
Ultra violet rays characteristic temperature
10^4-10^6 k
Visible rays characteristic temperature
10^3-10^4 k
Infrared rays characteristic temperature
10-10^3 k
Radio waves characteristic temperature
Less than 10k
What is R in the intensity formula?
Distance from the star (m)
Why doesn’t a black body curve ever hit the x axis?
It emits at all wavelengths- its a black body
What is area measured in?
Metres square
Which type of radiation has subunits for telescopes and what are they?
Infrared -
Near, mid, far
What’s wrong with using visible light as a telescope?
It doesn’t penetrate through dust clouds
Name the process involving photons going up
Absorption
Name the process involving photons going down
Emittion
What’s the key thing that multi wavelength astronomy does?
Provides extra information - not limited to visible light
What equations do we use to calculate the energy of a photon when given wavelength vs frequency?
Frequency
E=hf
Wavelength
E=hc
—
upside down y
If you have to choose a region of the electromagnetic spectrum which the wavelength of peak emission lies, what do you choose from?
Infared, visible, ultra violet
How do we explain a colour of a star, deducing it from the spectrum?
The (colour) end of the visible spectrum is nearer the peak, so it’s intensity is higher than the (opposite colour) end
What would be the observed feature on a spectrum of a star to show absorption/emission?
Absorption - dark lines at that wavelength
Emission - coloured lines at that wavelength
How do we explain why a star is a particular colour?
Peaks at (wavelength), so higher intensity of light at the (colour) end of the spectrum
When is a black body graph’s gradient at zero (apart from at the extremes)?
At the peak
What are continuous line spectra?
All visible wavelengths of light are present
What are continuous line spectra produced by?
The atoms of heated metals
How do you convert from Joulres to eV?
Divide by 1.60x10-19 (e on data sheet)
When doing ratio questions with powers emitted by stars, what is it important to remember?
Cross cancel where possible
Do not cross-cancel indices as they’re part of the numbers that we DO have!
If we’re drawing 2 black body curves on the same graph, what are three things we need to remember?
- Neither will hit 0
- They do not cross over each other
- For the cooler body, the entire curve is lower
What can be seen at radio e-m wavelengths (multi-wavelength astronomy)?
Pulsars
Cool stars
What can be seen at micro e-m wavelengths (multi-wavelength astronomy)?
Cosmic background radiation
What can be seen at infared e-m wavelengths (multi-wavelength astronomy)?
Star formation (can see through dust)
What can be seen at visible e-m wavelengths (multi-wavelength astronomy)?
Planets
Nebulae
What can be seen at UV e-m wavelengths (multi-wavelength astronomy)?
Stars
Supernovae
What can be seen at X-ray e-m wavelengths (multi-wavelength astronomy)?
Black holes and quasars
What can be seen at gamma e-m wavelengths (multi-wavelength astronomy)?
Black holes and quasars
Within which region of the e-m spectrum can black holes and quasars be seen?
X-ray and gamma
Within which region of the e-m spectrum can stars and supernovae be seen?
UV
Within which region of the e-m spectrum can planets and nebulae be seen?
Visibe
Within which region of the e-m spectrum can star formation be seen?
Infared
Within which region of the e-m spectrum can cosmic background radiation be seen?
Micro
Within which region of the e-m spectrum can pulsars and cool stars be seen?
Radio
Which part of the e-m spectrum can reveal star formation through dust?
Infared
Hottest and highest energy end of the e-m spectrum
Gamma
Coolest and lowest energy end of the e-m spectrum
Radio
How do we calculate A in Stefan’s law?
4 x pi x radius^2
What does a higher black body curve than another mean?
Higher temperature
Higher intensity (= higher brightness)
Describe the main features of the spectrum of a star and sate where in the star they arise?
Continuous spectrum due to radiation of all wavelengths emitted from the surface of the star
Line absorption spectrum due to passage of radiation through atmosphere of star
What should always be include in a multiwavelength astronomy question?
Link between wavelength and temperature
What do we explain when explaining why a star would look “bluer”?
Greater spectral intensity at the blue end
What do we need to remember to do if rearranging P = AoT^4 to work out a radius?
Multiply out the 4 and the pi first
What does multi wavelength astronomy give us?
Extra information
Why is the infrared part of the spectrum used to observe stellar formation?
Has a longer wavelength than the size of the dust particles = is not scattered by them
Penetrates the dust clouds in which the stars are being formed
How can absorbing elements be identified from an absorption spectrum?
From the wavelength of lines
