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Astro 103 > Astro Exam 1 (4/17/23) > Flashcards

Astro Exam 1 (4/17/23) Flashcards

1
Q

zenith

A

point directly over head

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2
Q

meridian

A

runs north through the zenith to south

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3
Q

altitude

A

height above the horizon, measured in degrees
0° = horizon, 90° zenith

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4
Q

estimating angles

A

earth moves 15° every hour

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5
Q

celestial sphere

A

earth is the center of a big ball and on it are the sun and stars

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6
Q

big dipper - polaris

A

pointer stars of the big dipper at the base point to Polaris (north star) almost directly above the north pole at all times

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7
Q

Polaris

A

at the north pole all the stars seem to rotate around Polaris
at the equator the NP is on the horizon so the stars no longer look like they rotate around the zenith because they are still rotating around Polaris (under the horizon)

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8
Q

circumpolar stars

A

never set and just go in a circle around polaris depending on where you are (whereas others rise in the east and set in the west)

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9
Q

time exposure

A

if the streaks of the stars are in a perfect circle all the way around then its a 24h exposure

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10
Q

ecliptic plane

A

earth’s orbit around the sun is in the shape of an ellipse on the ecliptic plane
constellations in the path the sun makes in a year = zodiac

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11
Q

ecliptic plane

A

earth’s orbit around the sun is in the shape of an ellipse on the ecliptic plane
constellations in the path the sun makes in a year = zodiac

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12
Q

winter solstice

A

Dec 21 - where the sun reaches a low altitude in the sky and rises and sets at the most extreme south due east and west
- never rises at high latitudes in the Northern Hemisphere (shortest day)
- never sets at high latitudes Southern Hemisphere (longest day)

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13
Q

summer solstice

A

June 21 - sun is much higher in the sky and rises and sets in the most extreme north due east and west
- highest point in the local sky in NH (longest day)
- shortest path in the SH (shortest day)

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14
Q

vernal/autumnal equinox

A

March 21/Sept 21 - when the sun rises exactly on the east and exactly on the west
- the angle of the axis with respect the ecliptic plane and the north and south poles is not perpendicular (tilted 23°)

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15
Q

seasons

A

created by the tilt of the earth
- high altitudes: north = 24h daylight, south = 24h darkness

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16
Q

north star consistency

A

earth’s axis wobbles - doesn’t change the seasons because the wobble takes 26,000 years
over the course of these years the north star changes
- during Egyptian times it was Thuban and in the future it will be Vega

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17
Q

sun at zenith

A
  • reaches the zenith at midday on the equator/ in the tropics on the March and Sept equinoxes
  • at the tropic of cancer, the sun is at its zenith during the summer solstice
  • tropic of Capricorn the sun is at the zenith during the winter solstice
  • in between those bands it reaches the zenith several times a year
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18
Q

arcminutes

A

1 degree = 60 arcminutes that are broken up by 60 arcseconds

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19
Q

small angle formula

A

angular size = physical size * 360°/2π*distance

physical size = angular size * 2π*distance/360°

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20
Q

moon orbit

A

29 1/2 days

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21
Q

moon size and distance

A

moon’s diameter is about 1/4 of the earth’s diameter, roughly the size of north America
moon is about 30 earth diameters away from he earth (239,000 miles)

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22
Q

phases of the moon

A

1st quarter moon rises at noon and reaches its highest point at sunset
full moon rises at sunset and reaches its highest point at midnight
3rd quarter moon rises at midnight and reaches highest point at sunrise
new moon rises at sunrise and reached its highest point at noon
- whatever phase the moon is in the earth is the opposite phase (new moon = full earth view from the moon)

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23
Q

lunar eclipse

A

occurs because the moon is passing through the shadow of the earth during the full moon phase

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24
Q

umbra

A

full shadow

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25
Q

penumbra

A

partial shadow

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26
Q

total lunar eclipse

A

fully reddish moon means the moon is directly in the umbra - common occurrence but can only be seen by the side of the earth that is in night

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27
Q

partial lunar eclipse

A

partially dark moon

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28
Q

penumbra lunar eclipse

A

looks like a normal full mon

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29
Q

solar eclipse

A

when the moon moves into the sun’s shadow
much rarer than lunar eclipse because the moon is much smaller than the earth and can only be seen from the small area that the moon’s shadow takes up
causes the moon to block out the sun

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30
Q

Aristotle

A

separation between the Earthly and the heavenly
champion of the geocentric (earth-centered) model
earthy is stationary and the sky revolves around us

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31
Q

the greeks: round earth

A
  • constellations change as one moves north and south
  • ships disappear hull first over the horizon as if its dropping over a curved surface
  • earth’s shadow on the moon during eclipses is curved
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32
Q

the greeks: size of the earth

A
  • Eratosthenes determined it by looking at stick shadows in different cities
  • the bigger the difference in shadow length the larger the angle of curvature of the earth
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33
Q

ptolemy

A

refined aristotle’s model
explained retrograde motion: mars is orbiting on its epicycle = a circle around a larger circle which means that every now and then it will seem to go backwards
added as many epicycles as he wanted

34
Q

Ptolemy

A

refined aristotle’s model
explained retrograde motion: mars is orbiting on its epicycle = a circle around a larger circle which means that every now and then it will seem to go backwards
added as many epicycles as he wanted

35
Q

Copernicus: uniform circular motions

A

heavenly body should always move in a perfect circle

36
Q

Copernican Principle

A

the earth is not the center of the universe
- planets closest to the sun have faster orbits but that speed never changes

37
Q

Copernicus: retrograde motion

A

optical illusion of an inner planet passing an outer planet - like runners on a track if you pass someone and look back they seem to be moving backwards

38
Q

Copernicus: parallax

A

if he was right that the earth goes around the sun then the stars should seem to shift over the course of the year but he argued that they were so far away you couldn’t see the difference

39
Q

Tycho Brahe

A

rich man that recorded the best astronomical observations because he could afford the resources
provided Kepler with data

40
Q

Tycho’s Model

A

Earth at the center and the mon orbiting the earth with the sun on the outside and all the other planets orbiting the sun

41
Q

Kepler: platonic solids

A

dodecahedron - ether
tetrahedron - fire
octahedron - air
icosahedron - water
cube - earth

42
Q

Kepler: mars

A

almost got the correct orbit, off by 8 arc minutes
abandoned the concept of circular orbit

43
Q

Kepler’s Law #1

A

planets travel in elliptical orbits with the sun at one focus

44
Q

Kepler: foci of an ellipse

A
  • foci of the ellipse determine how stretched out it will be, the sun lies at one and nothing at the other
45
Q

Kepler: extreme distances in ellipse

A
  • two extreme distances, closest: perihelion, farthest = aphelion (add them together = 2x semi-major axis)
46
Q

Kepler: eccentricity

A

measure of how squished an ellipse is, ranges from 0 = circle to 1 = more elliptical and stretched

47
Q

Kepler: Mars

A

Mars’ orbit was so difficult to figure out because the eccentricity of Mars = 0.09, meaning its almost a circle, and its speed changes

48
Q

Kepler’s Law #2

A

a line from the sun to a planet sweeps out equal areas in equal times
- planets move faster when they are nearer to the sun

49
Q

Kepler’s Law #3

A

P² = a³
- p units of earth years
- a units of AU
- 1 AU = the average distance from the earth to the sun
- 1 AU = 93 million miles
- perihelion distance - d = a(1-e)
- aphelion distance - d = a(1+e)
- where e = eccentricity

50
Q

Newton’s tides

A

caused by the difference in the strength of the moon’s gravity between the “near” and “far” sides of the earth

51
Q

Tidal force

A

stretches the oceans out and the earth rotates “under” these bulges causing the daily tides

52
Q

spring tides

A
  • highest high tide, lowest low tide
  • sun’s gravity also contributes to the ocean tides but not as much as the moon’s gravity does
  • when the sun and moon are in line (new and full moons) the tides are more extreme than average
53
Q

neap tides

A
  • lowest high tide
  • highest low tide
  • during 1st and 3rd quarter moons when tides are less extreme than average
54
Q

light wave equations

A

λf = c, c speed of light (m/s), frequency (Hz)

E - hf, the energy of the photon (Jules), “Planck’s constant” h = 6.63 x 10-34 Joules*s, frequency (Hz)

55
Q

types of light

A

visible, ultraviolet, x-rays, gamma rays, infrared, microwaves, radio waves

56
Q

wavelength and frequency

A

inverse relationship
as the wavelength gets smaller the frequency is higher and vise versa

57
Q

Max Planck

A

explained certain spectra by proposing a “distasteful” idea that energy comes in discrete amounts called quanta

58
Q

Bohr’s hydrogen model

A
  • not very accurate
  • proton in the middle, electrons orbit around
  • electron energy levels (integers only)
  • the energy of the wave of light equals the difference in energy from the higher level to the lower level
59
Q

Law of conservation of energy

A

energy is neither created nor destroyed but it can change forms

60
Q

spectral lines

A

each element has a unique set of spectral lines, always emitted at the same wavelgihtsn
can be used to measure
- Chemical composition, temperature, density, magnetic fields, and motion towards or away from an observer

61
Q

Doppler effect

A

moving away means red shift = lager wavelengths
moving towards means blue shift = smaller wavelengths
- no shifting sideways only approaching and moving away
- pattern of colors don’t change

62
Q

Doppler effect equation

A

Speed of the object divided by the speed of light = observed wavelength - original wavelength divided by the original wavelength

Ex = 501-500/500 = 1/500 = v/c
V = 1/500 speed of light

63
Q

continuous spectra

A
  • solid rainbow band emitted by solid objects
  • composition doesn’t change depending on object
64
Q

Stefan-Boltzmann Law

A

Power/m2 = σT4
- σ =5.7x10-8W m-2K-4

hotter blackbodies emit more total energy

65
Q

Wien’s Law

A

hotter blackbodies emit more of their light at shorter wavelengths

ƛ = 2.9 x 10⁶ * K/ T

66
Q

absorption line spectrum

A

some parts are dark but with many lines of orange, blue and purple = neon spectrum

67
Q

emission line spectrum

A

mostly dark with a single line of red, blue, and purple = hydrogen

68
Q

filament temperature

A

lower filament temp = dim bulb and reddish light
hotter filament temp = brighter bulb and blueish light

69
Q

telescope

A

the light-gathering ability of the telescope increases as the area of the telescope increases
- Area = πD2/4 = πr2
- larger diameter is better

70
Q

diffraction limit

A

aka resolution = measure of how sharply the telescope can make an image
- two stars not resolved look like one and the diffraction limit is the point where you can just barely tell there are two

resolution = 250,000(𝛌/D)
- smaller is better
- the longer the telescope, the worse the resolution

71
Q

refracting telescope

A
  • lens at the top, then empty pipe, and the eyepiece to focus
  • no longer make telescopes with lenses because they are top heavy and bigger lenses bend under their own weight
72
Q

refracting telescope: chromatic aberration

A

reddish and bluish tinge because the lens is trying to bring the different color wavelengths into focus at the same time, can be minimized by adding extra lens but cannot be completely resolved

73
Q

Refractors

A

Dearborn 18.5” - used to be the biggest refracting telescope in the world
Now Yerkes Observatory 40 in diameter and 60ft length

74
Q

Newton’s reflecting telescope

A
  • uses a mirror to reflect the light off of
  • curved mirror
  • front of the telescope is open with a curved mirror at the bottom end and then bounces the light to the eyepiece from the side or back
  • immune to chromatin aberration
75
Q

William Herschel

A

discovered:
- infrared light - calorific rays
- Georgium Sidus = Uranus
- built 2 large telescopes

76
Q

Keck

A
  • honeycomb-shaped mirror
  • Hexagon pieces fitted together
77
Q

“Seeing”

A
  • how steady of calm the atmosphere is when observing
  • bad “seeing” = a rippling effect
  • higher altitude is better because the atmosphere is clearer and there is usually less light population
78
Q

hubble space telescope

A

above the atmosphere, no “seeing” probelms
studies infrared and ultraviolet rays of light that can only be seen about earth’s atmosphere
infrared light penetrates dust clouds

79
Q

james webb telescope

A

only observes infrared wavelenghts, hexagonal mirror design

80
Q

grote rebber - radio telescope

A

first radio telescope, radio waves are much longer so for higher resolution the diameter needs to be much bigger
- Very Large Array: take multiple radio telescopes and link them electronically to have a higher resolution
- Stitched together images from radio telescopes around the world for the first black hole photo (Messier 87)

Astro 103 (3 decks)

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