Space Flashcards
Parallax and parsecs
1 arc minute = 1/60 of 1 degree
1 arc second = 1/3600 of a degree
1 parsec is the distance at which 1 A.U subtends a parallax angle of 1 second
1 AU = 1.496x10^11m
What is the cosmological principle?
Universe is isotopic - appears the same in all directions
Universe is homogenous - constant matter density
Doppler shift?
Δλ/λ = v/c
Δf/f = v/c
v = recession speed
A moving object will cause the wavelength of the waves to change
The wavelength waves in front of the source decreases and the frequency increases
The wavelength behind the source increases and the frequency decreases
Red shift:
Light from distant galaxy is shifted towards the end of the spectrum
Evidence that the universe is expanding
Hubbles law?
Recession speed of a distant galaxy is directly proportional to its distance from the earth
V = Hod
Age of the universe?
1/Ho
Big Bang theory
Time and space created
Universe expands rapidly in a period of inflation
First fundamental particles gain mass
Quarks bind to form hadrons (protons and neutrons)
As the universe is expanding its cooling
The universe cools enough for atoms to form
The nuclei capture electrons. EM radiation from this stage is now detected as cosmic background radiation
Cosmic background radiation
Main pieces of evidence for the Big Bang
Radiation released as gamma rays but it’s now been stretched to microwaves
Accounts for the temperature of 2.7K
Dark energy?
Energy of empty space, seems to fuel the expansion of the universe.
Extremely mysterious
Star formation?
An interstellar dust cloud collapses under gravity
The GPE decreases and the KE increases and thus the temperature
Once the temperature reaches 10 million K, hydrogen nuclei fuse into helium
Radiation and gas pressure = gravity
Hertzpring Russel diagram
Y axis = luminosity
x axis = temperature (increases to the left)
White dwarfs = lowest luminosity
Main diagonal = main sequence
Blue supergiants = high luminosity and temperature
Red supergiants = high luminosity low temperature
Red giants = medium luminosity medium temperature
What is the chandrasekah limit?
Maximum mass of a white dwarf. It is 1.4 solar masses
Energy levels
Only specific energy are allowed
Most negative energy levels is the ground state
n=1 = -13.6ev
n=2 = -3.4ev
n=3 = -1.5 eV
n=4 = -0.85ev
Negative values as energy needs to be inputted to remove electrons
Photon absorbed = up energy levels
Photon emitted = down energy levels
1) E = hc/λ (photon wavelength)
2) E = hf (frequency)
Emission and absorption spectra
Emission spectrum - hot gas emits photons, only certain energy levels are allowed so only certain wavelengths are seen
Absorption spectrum caused when a hot gas absorbed photons. Only certain frequencies can be absorbed. Hence dark lines are on a continuous spectrum background
Diffraction gratings
dsinθ = nλ
Diffraction experiment
Measurements:
With a ruler measure the distance to the screen D and the distances from the central max to the fringes
Take each measurement multiple times to improve accuracy
Analysis:
Calculate the corresponding angle using θ = tan-1 (x/d)
Calculate d using 1/N where N is the number of lines per m
Plot a graph of n against sin θ
Graph should be a straight line through the origin with a gradient of d/λ
λ = d/m where d = line spacing and m = gradient
