Exam 3

Question 1

William Herschel

Answer 1

• 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

Question 2

Thomas Wright

Answer 2

• MWG is a flattened distribution of stars; slab that forms part of a shell
• speculated that faint nebulae were stars in other galaxies

Question 3

Immanuel Kant

Answer 3

• 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

Question 4

Friedrich Bessel

Answer 4

• 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

Question 5

Jacobus Kapetyn

Answer 5

• 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

Question 6

Henrietta Leavitt

Answer 6

• discovered Cepheid variables
• found over 1500 in the Small Magellanic Cloud
• brighter Cepheid variables have a longer period of variability

Question 7

Harlow Shapley

Answer 7

• 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

Question 8

Heber Curtis

Answer 8

• 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)

Question 9

James Campbell Maxwell

Answer 9

• 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)

Question 10

Max Planck

Answer 10

• 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

Question 11

photoelectric effect

Answer 11

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

Question 12

uncertainty principle

Answer 12

electrons don’t have precise velocity or position, and it can not be precisely predicted

Question 13

DeBroglie

Answer 13

if waves behave like particles, particles can behave as waves too
- postulated that electrons can behave like waves

Question 14

Erwin Schrodinger

Answer 14

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

Question 15

Drake equation

N = R….

Answer 15

calculates probability pf discovering intelligent life on other planets

if N≤1, we are the only intelligent life in the Universe

Question 16

Werner Heisenberg

Answer 16

created the uncertainty principle

Question 17

Neils Bohr

Answer 17

created the Bohr model of the atom
- explained emission spectra

Question 18

proton-proton chain

Answer 18

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

Question 19

Doppler Wobble

aka radial velocity level

Answer 19

• 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

Question 20

Astrometric Wobble

Answer 20

• 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

Question 21

Transit

Answer 21

• 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

Question 22

Hubble Constant

Answer 22

70/km/s/Mpc

70 kilometers/sec/Megaparsec

units of inverse time (1/time)

Question 23

George Lemaitre

Answer 23

• 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

Question 24

cosmological redshift

Answer 24

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

Question 25

gravitational redshift

Answer 25

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

Question 26

Doppler effect

Answer 26

if an object is moving away, the spectrum shifts towards longer wavelengths
- amount of shift depends on the speed of the object

Question 27

Hubble Law

Answer 27

velocity = Hnaught (current rate of expansion) x distance