The Scientific Method
- And is FALSIFIABLE
UNIT 1: The Electromagnetic Spectrum
- Astronomical information is transmitted by starlight.
- Starlight the star’s temperature, chemical composition, motion, pressure, magnetic fields etc.
The EM Spectrum
- Light: mutually perpendicular oscillating electric and magnetic fields.
- Light: moves in wavelike pattern at a speed of c= 3 x 10 m/s.
- Wavelength, λ: distance between peaks of wave.
- Tachyons: theoretical faster-than-light particles.
1 nanometer = 1nm = 1 m = 1 x 10 m = 10 m
λred = 700nm = 700 x 10 = 7 x 10 m -7
λviolet = 400nm = 400x10 = 4 x 10 m
Visible Colors: ROY G BIV Photons: bundles of energy light as a particle
Frequency = f
= number of wave peaks passing a given point each second.
= number of waves/second
= complete cycles/second
f = c/λ
fred= 3 x 10 m/s / 700 x 10 m-9
= 4.3 x 10 cycles/s
= 4.3 x 10 Hz
- Get star in telescope
- Sequence of colored filters at eyepiece end of telecope
Wien Formula Calculation T= 0.0029 m · k / 550 x 10 m -9
T= 5272.7 ~ 5300k
- Note that the surface temperature of the Sun is ~ 5800k
Energy of Light
E red= (6.625 x 10 -34J·s)
E red= (6.625 x 10 J·s) (4.3 x 10 cycles/s)
E red.85 x 10 -19J
Note: shorter wavelengths higher frequencies and energies.
Kirschoff’s (Three) Laws of spectral analysis
The Bohr Model of The Hydrogen Atom
Proton carries positive charge
Electron carries negative charge
1913: Electron is in circular orbit around the proton.
The Doppler Effect in Astronomy
Direction of Motion:
Obtain spectrum of a stationary (= NOT moving) source (e.g. hydrogen) in the laboratory.
Obtain spectrum of a moving object (e.g. a star)
Compare the two spectra
C = speed of light = 3 x 10 m/s
∆λ = wavelength difference between lab and stellar spectra = wavelength difference between lab and
Λlab = wavelength on lab spectrum
V r radial velocity of star
Then, V = C∆λ/ Λlab
V r (3 x 10 m/s) (434.1-434)nm/ 434 Radial Velocity Problem
H spectral is λ = 656.2850nm in the lab. Same line is λ = 656.2957 nm in the spectrum of Regulus. Is
Regulus approaching or receding ? Radial velocity?
This Hα line has a LONGER wavelength in the spectrum of Regulus
Spectrum is red-shifted
Moving away from us
V r C∆λ/ Λlab = (3x10 m/s) (656.2927-656.2850)nm / 656.2850 nm
V r 3500 m/s = 3.5km/s
Using the Doppler Effect, how can you tell that our sun rotates?
UNIT 2: The Universe
Distance Units in Astronomy
Lightyear = ly: Distance that light travels in one year, 1 ly = 9.5 x 10 m
Parsec = pc: 1 pc = 3.26 ly
Astronomical unit = AU: Average distance between the Earth and Sun
The Hubble Law
Nebula means cloud in latin, Nebulae is the plural form.
A galaxy is a large assemblage of stars which orbit a common center
All held together by gravity
Contains from a few thousand to trillions of stars
Hubble and Humason determined the distances and radial velocities of faraway galaxies
All faraway galaxies are redshifted and receding from us.
Andromeda Galaxy is coming towards the Milky Way
HUBBLE LAW: radial velocity of a galaxy is directly proporational to distance Farther galaxies are
V r d
V r H do(Hubble parameter)
d = V /H
H oV /r 1. The Universe is expanding.. space itself is expanding
Cosmic Microwave Background Radiation = CMB
1965: Arno Penzias and Robert Wilson radio astronomers at Bell Labs N.J.
Worked with the first communications satellite, TELSTAR.
Detected a persistent radio hiss from all directions in the sky
At a wavelength of 1.063 x10-3
The Wien Formula:
T= 0.0029 m·k /λdom
T= 2.728 ± 0.004K
= Temperature of empty interstellar space.
Some event must have HEATED the Universe
Penzias and Wilson discovered the remnant (leftover) heat from the birth of the universe.
1. The Universe is expanding.
2. There was a heat event at the beginning of space and time as proven by the CMB.
Thus the Universe originated in an explosive event called the Big Bang.
1989: Cosmic Background Explorer Satellite (COBE) launched.
Provided an above-atmosphere measurement of the CMB.
Confirmed that the CMB is 2.728 +/- 0.004 K
Further CMB Confirmation
2001: Wilkinson Microwave Anisotropy Probe (WMAP) launched.
It has a 30 times resolution greater than COBE
Confirmed the value of the CMB.
Still giving info about the Universe’s composition, geometry, history and the amount of matter
within it. The Cosmological Principle
The Universe is:
1. Isotropic: It looks the same in all directions
2. Homogeneous: Matter is approximately evenly and uniformly distributed. Every region is the
same as every other region.
3. Universal: the laws of physics are the same everywhere.
History of the Universe
Time after Big Bang Event
<1/1000 s, T= 1 x10 K All types of elementary particles in
4s existence. Particle transmutations
3 minutes occurs.
30 minutes Matter and anti-matter begin
380,000 years, T = 3000k annihilation to produce energetic
1 x 10 years photons.
2 x 10 years Netutrons and protons fuse to form
? years Helium Nuclei
Elementary particle transmutations
Recombination Era photon energies
have declined enough such that
Hydrogen and Helium ATOMS can
The Age of the Universe = Hubble Time
Recall the Hubble Law:
V =H d where we use a Hubble parameter of 75 km/s ÷ Mpc
Since d = v t replace d in above equation:
v = o v t
1 = o t
t = 1/o = Hubble time = Age of Universe
T =1÷ 75km/s ÷ Mpc t = Mpc÷75km/s
t = 3.09 x 10 km ÷ 75 km/s
t = 4.12 x 10 s
t = 13.1 x 10 years
Types of Universe
Open Universe: Density of matter is low gravity is weak Universe expands forever.
Closed Universe: Density of matter is high gravity will halt the expansion Universe will re-contract
If this happens repeatedly, we have an oscillating Universe
Flat Universe: Universe contains the so-called critical density of matter galaxies barely manage to
Future of an Open or Flat Universe
Time after Big Bang
1. 1 x 10 years
2. 1 x 10 14
3. 1 x 10 years
4. 1 x 10 years
5. 1 x 10 years
6. 1 x 10 100years
7. Far Future
Hydrogen and helium are depleted no new stars can form
Existing stars run out of fuel
All stars will have experienced ~ 100 disruptive encounters, flinging their planets into space.
Evaporation of stars and collapse of galaxies into the central Black Holes
Protons decay (???)
p e + v (a positron and neutrino)
e +e Y (a photon = a burst of radiative energy)
Hawking Black Holes decay
The Big Fizzle = an ever-expanding gas of electrons, protons, neutrons, photons
Future of a Closed or Oscillating Universe 1. The expansion phase = statements 1. through 5. above.
2. At some unknown future time, re-contraction begins.
The density of the universe increases, the number of Black Holes increases, they feast on
everything within reach.
3. Black Holes will meet and coalesce (merge) into ONE Black Hole
= the Universe = the new singularity
= THE BIG CRUNCH
How to Decide among these Futures
Is there sufficient matter to exert a strong gravitational force?
≥ 5 protons per m of space
gravity will dominate and re-contract the Universe.
a close or oscillating Universe
< 5 protons per m of space
Gravitational attraction among all particles is insufficient to “close” the Universe.
An open Universe that expands forever
Density Measurement of Universe
The sum of all observed, luminous matter
NOT enough matter to re-collapse the Universe
What about non-luminous matter?
Clouds of dark gas, planets, dead stars, black holes, neutrinos… DARK MATTER (Vera Rubin)
The Ultimate fate of the Universe is still undetermined.