Exam 3 Flashcards
William Herschel
- assembled one of the first maps of the Milky Way in 1785
- correctly concluded that it was a disc shape, 5x wider than thick
- assumed stars were all evenly distributed, didn’t know about dust that made some stars look further away
- discovered Uranus
Thomas Wright
- MWG is a flattened distribution of stars; slab that forms part of a shell
- speculated that faint nebulae were stars in other galaxies
Immanuel Kant
- modeled distribution of stars in MWG; MWG was a rotating flattened disk like the Solar System
- galaxies as “Island Universes”
- believed the Universe changed over time
Friedrich Bessel
- First to measure a parallax (1838); 61 Cygni with a parallax of 0.31 arcsec (close to the actual value)
- proved that telescopes are needed to calculate parallax
Jacobus Kapetyn
- mapped the distribution of stars in the MWG
- MWG was a disc 17,000 parsecs (17 kpc) across
- Sun was near the center of the galaxy
Henrietta Leavitt
- discovered Cepheid variables
- found over 1500 in the Small Magellanic Cloud
- brighter Cepheid variables have a longer period of variability
Harlow Shapley
- used globular clusters to 3D map the MWG
- Sun was ~2/3 of the way from the center of the galaxy
- MWG was huge (incorrect)
- thought MWG was the entire Universe (incorrect)
- participated in the Great Debate
Heber Curtis
- MWG was much smaller that Shapley said (correct)
- multiple galaxies make up the universe; spiral nebulae were distant galaxies
- sun is the center of the MWG (incorrect)
James Campbell Maxwell
- unified concept of electric and magnetic (electromagnetic) force with light
- light is a wave in the same medium that causes electric and magnetic phenomena
- electric and magnetic fields travel at speed of light (c)
Max Planck
- explained how radiation is emitted and absorbed by a hot object (thermal emitter) with the idea of quantized energy (quantum radiation)
- intensity of light emitted by hot objects has a very specific shape that varies by temperature
- Planck found an equation that explained the shape (couldn’t be explained by classical electromagnetic theory), but it necessitated energy released in discrete amounts (quantized energy
Einstein used Planck’s idea of quantized radiation to explain the Photoelectric Theory
photoelectric effect
hitting metal with light creates a current, causes electrons to be ejected
can’t be caused by light as a wave, must have particle properties
uncertainty principle
electrons don’t have precise velocity or position, and it can not be precisely predicted
DeBroglie
if waves behave like particles, particles can behave as waves too
- postulated that electrons can behave like waves
Erwin Schrodinger
created the Schrodinger equation; tells how things move based on forces that are applied to them
- applies to things that are too small to be governed by Newtonian laws of motion
- describes how waves interact on the quantum level
also created the electron cloud model of the atom
Drake equation
N = R….
calculates probability pf discovering intelligent life on other planets
if N≤1, we are the only intelligent life in the Universe
Werner Heisenberg
created the uncertainty principle
Neils Bohr
created the Bohr model of the atom
- explained emission spectra
proton-proton chain
fusion events where protons overcome repulsion in extreme heat to combine
- the fusion that occurs in stars, creating heavier and heavier elements
- energy is produced (E=mc^2) when mass is lost (m) as protons fuse
- requires quantum mechanical tunneling
- creates the energy that fuels stars and keeps them held up agains the gravity of their core
4 H (4 protons) combine to become 1 He (2 protons), energy is released
Doppler Wobble
aka radial velocity level
- method of detecting exoplanets
- as a planet orbits a star the wavelengths of light released get shorter and longer (wobble)
- works best when facing edge-on
- shift in wavelength is larger for more massive objects (most exoplanets have very small shifts)
measures Doppler shift
Astrometric Wobble
- method of detecting exoplanets
- slight wobble in a star’s orbit caused by the gravity of an orbiting planet
- gives info on the mass of the planet and on the period of its orbit
measures positional shift
Transit
- method of detecting exoplanets
- planet travels in front of its star, causing a dip in the omission spectrum (due to the planet blocking the light)
used by Kepler and TESS
Hubble Constant
70/km/s/Mpc
70 kilometers/sec/Megaparsec
units of inverse time (1/time)
George Lemaitre
- showed that one of the solutions to Eistein’s GR was an expanding universe
- spectra of distant galaxies are redshifted in proportion to their distance
- derived the rate of expansion before Hubble published his paper
cosmological redshift
light waves are stretched as space expands, increasing wavelengths
NOT CAUSED BY DOPPLER SHIFT
not caused by mvmt of galaxy (like doppler) but by expansion of space
gravitational redshift
pull of gravity causes lightwaves to lose energy as they fight to escape (things like pull of a black hole) which causes lightwaves to lengthen
Doppler effect
if an object is moving away, the spectrum shifts towards longer wavelengths
- amount of shift depends on the speed of the object
Hubble Law
velocity = Hnaught (current rate of expansion) x distance
