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Astronomy > Midterm > Flashcards

Midterm Flashcards

1
Q

Light year

A

distance light travels in a year
=9.6x10^12 km about 10^13 km

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2
Q

Astronomical unit

A

AU = 1.5x10^8 km
Earth-Sun Distance

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3
Q

Parsec

A

pc = 3.1x10^13 km
about 3 lyr

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4
Q

nanometer

A

10 Angstrom

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5
Q

Distance of sun

A

8 light-minutes

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6
Q

Nearest Star

A

1 parsec = 3.3 light years

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7
Q

size of milky way

A

90000 light years

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8
Q

Nearest galaxy

A

10 million light years

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9
Q

Clusters of Galaxies

A

1 billion years = Gigayear = Gyr

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10
Q

Galaxies forming

A

10 Gyr

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11
Q

Cosmic Microwave Background

A

14 billion years

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12
Q

1x10^18

A

Exa E

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13
Q

1x10^15

A

Peta P

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14
Q

1x10^12

A

Tera T

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15
Q

1x10^9

A

Giga G

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16
Q

1x10^6

A

Mega M

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17
Q

1x10^3

A

Kilo k

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18
Q

1x10^-2

A

Centi c

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19
Q

1x10^-3

A

Milli m

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20
Q

1x10^-6

A

Micro u

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21
Q

1x10^-9

A

Nano n

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22
Q

1x10^-12

A

Pico p

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23
Q

1x10^-15

A

Femto f

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24
Q

1x10^-18

A

Atto a

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25
Q

Statistical (noise) uncertainty

A

not enough data

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26
Q

Systematic uncertainty

A

incorrect assumption

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27
Q

Scientific method

A

Prediction
Experiment to test model
Revise or keep same
Model (theory)

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28
Q

celestial sphere

A

the inverted dome you see the stars on

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29
Q

Zenith on celestial sphere

A

the point overhead

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30
Q

Local celestial meridian

A

runs from the N to S through Zenith

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31
Q

Altitude

A

the vertical angle on the celestial sphere

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32
Q

Azimuth

A

the horizontal angle from north or south

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33
Q

New Moon

A

0 days
nothing
rises at noon
sets at sunset

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34
Q

First Quarter

A

7 days
half
rises at sunset
sets at midnight

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35
Q

Full Moon

A

14 days
full
rises at midnight
sets at sunrise

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36
Q

Third Quarter

A

21 days
half
rises at sunrise
sets noon

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37
Q

Waxing crescent

A

2-6 days

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38
Q

Waxing gibbous

A

8-13 days

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39
Q

How far does the moon move per day?

A

12 deg/day

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40
Q

Period of the moon

A

4 weeks - 28 days

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41
Q

The phases of the moon are caused by …

A

the moon’s position around the Earth in relation to the sun.

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42
Q

Waning gibbous

A

15-20 days

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43
Q

Waning Crescent

A

22-27 days

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44
Q

Nadir

A

Point on the celestial sphere directly underneath

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45
Q

celestial equator

A

projection of earth’s equator onto the celestial sphere

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46
Q

north celestial pole

A

projection of earth’s north pole onto the celestial sphere

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47
Q

constellations

A

unrelated stars
only appear to be close together

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48
Q

Earth spins on its axis every …

A

~ 24 hours

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49
Q

Earth orbits the Sun in …

A

~ 365 days

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50
Q

Earth’s axis precesses on a …

A

26000 year cycle

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51
Q

Moon orbits Earth …

A

~ 28 days

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52
Q

Planets orbit Sun …

A

in a variety of of periods

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53
Q

Proper motion of stars

A

very small
less than 1 arcsec/century

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54
Q

degree

A

circle divided into 360 parts

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55
Q

arcminute

A

degree divided into 60 parts

56
Q

arcsecond

A

arc minute divided into 60 parts

57
Q

angular size

A

apparent angle between objects on the sky

58
Q

noon is defined as …

A

the Sun crossing “local meridian”

59
Q

One solar day

A

24 hours from noon to noon

60
Q

the sun’s apparent path on the sky is called the …

A

Ecliptic
the ecliptic is also the projection of Earth’s orbit onto the celestial sphere

61
Q

What does sidereal mean?

A

compared with the stars

62
Q

Are sidereal time and Solar time the same?

A

no

63
Q

Sidereal time is …

A

the time it takes for a star to come back to the same meridian
23 hours 56 minutes

64
Q

Who is sidereal time good for?

A

astronomers

65
Q

Who is solar time good for?

A

people

66
Q

lunar eclipse

A

the Earth casts a shadow and the Moon can sometimes pass through it

67
Q

Where can a solar eclipse be seen from?

A

a small area on earth
50 miles

68
Q

Where can a lunar eclipse be seen from?

A

the entire night side of the Earth

69
Q

Line of Nodes

A

where two orbital planes cross

70
Q

When can a solar eclipse occur?

A

When a new moon passes a node

71
Q

When can a lunar eclipse occur?

A

When a full moon passes a node

72
Q

size of the moon and sun from earth

A

.5 degree

73
Q

during a total solar eclipse what can you see of the sun

A

chromosphere and corona

74
Q

Small angle formula

A

angle a = 206265 c d/D
d is size of object
D is distance to object
angle in arcsec

75
Q

Angle of sun

A

32 arcmin

76
Q

Angle of moon

A

33 arcmin

77
Q

Composition of sun

A

ball of gas with no solid surface

78
Q

Density of sun

A

decreases from the center out

79
Q

Temperature of corona

A

1 million degrees

80
Q

Temperature of chromosphere

A

10000 K

81
Q

Temperature of photosphere

A

5800 degrees

82
Q

Temperature of sunspots

A

slightly cooler than photosphere

83
Q

Apogee

A

position furthest away from eath

84
Q

perigee

A

position closest to earth

85
Q

Perihelion

A

position closest to the sun

86
Q

aphelion

A

position furthest away from the sun

87
Q

Annular solar eclipses

A

happens when earth is near perihelion and moon is near apogee
see more of the sun

88
Q

What does the distance change about viewing the moon and sun

A

angular distance varies

89
Q

What causes seasons

A

the tilt of the earth makes the sun appear lower in winter and higher in summer
less sun = colder

90
Q

Does the obliquity of earth’s orbit cause seasons

A

no

91
Q

when does the sun’s ecliptic cross the equator

A

vernal equinox about mar 21
autumnal equinox about sep 23

92
Q

When are the highest and lowest points of the sun

A

Summer solstice about June 21
winter solstice about dec 21

93
Q

Celestial coordinates

A

position of every object defined by Ra, Dec and epoch

94
Q

Precession

A

wobbling of Earth’s axis of rotation around the vertical w.r.t
it takes 26,000 years
the celestial north pole follows a circular pattern

95
Q

Cosmology 400 BC to 1500 AD

A

earth at center of the universe
planets moved in perfect circles
planets move with a constant velocity
stars just beyond saturn

96
Q

Aristotle - 300 BC

A

student of Plato
studied through thought not experiment
his understanding ruled for next 2000 years
5 elements - earth, air, fire, and water + quintessence which makes up celestial bodies
objects with bases in nature (earth, water) sink while more perfect nature rises to perfect heavens
Earth is at the center, planets in perfect circles, stars are perfect and unchanging
Heavy objects fall faster
objects fall at a constant rate
Philosophy became catholic doctrine through Thomas Aquinas

97
Q

Aristarchus - 260 BC

A

believed sun was larger than earth
thought earth moves around sun
predict star brightness varied with the seasons
the universe must be large because no variation in position or brightness of stars
Parallax - seeing a star or planet from two locations should produce a shift in its apparent position on the sky

98
Q

Parallax

A

seeing a star or planet from two locations should produce a shift in its apparent position on the sky
viewing from two positions can estimate distances

99
Q

Who measured mars’ parallax and when
using what

A

Cassini in 1673
Paris to Africa

100
Q

Motion of outer plannets

A

not a constant rate

101
Q

Ptolemy - 100 BC

A

Born and worked in Egypt
First to carefully measure motions of planets
Published observations in Almagest
invented epicycle to use circle to fit planet motion
Islamic astronomers continued his work until 1100 AD

102
Q

Retrograde Motion in Geocentric Model

A

Epicycles are used to make sense
Point A moves around the earth in a constant circular motion
Planet P moves around the epicycle in a constant circular motion

103
Q

The eccentric epicycle

A

the earth is offset from the orbit center

104
Q

the equant epicycle

A

constant velocity about a point not centered

105
Q

Copernicus - 1500 AD

A

publishes a heliocentric model
explains retrograde motion
keeps perfect circles and uniform motion

106
Q

Copernican Revolutions

A

We are not the center of the Universe
The earth is not the center of the solar system - 1500s
The sun is not at the center of the Milky Way Galaxy - 1920s
The Sun is an average star in an average Galaxy - 1900s
Atoms make up <5% of the matter in the Universe - 1990s

107
Q

Retrograde motion in heliocentric model

A

Earth orbits more quickly than the outer planets. It catches up and passes the slower outer planets
Inner planets Mercury and Venus never appear far from the sun because they orbit the sun

108
Q

Tycho Brahe - 1570

A

Build best observatory of time to measure star and planet positions
-could measure positions to an arcminute accuracy
realized heavens are not perfect and unchanging
model was a hybrid of Aristotle and Copernicus
Earth at center but planets move around sun - didn’t work well

109
Q

Johannes Kepler - 1600

A

used data of Tycho to break Aristotle’s hold on universe
discovered 3 rules that describe motions of planets

110
Q

Kepler’s Law #1

A

Planets trace out ellipses with the Sun as one focus
planet orbits are only slightly elliptical

111
Q

Kepler’s Law #2

A

planets sweep out equal areas in equal times
planet moves faster when close to the sun than further away

112
Q

Kepler’s Law #3

A

The orbital period of a planet, P, depends on its distance from the Sun, “a”, such that: Period squared = distance cubed
period in years, distance in Astronomical Units

113
Q

Galileo Galilee - 1600

A

Used the telescope to prove planets go around the sun
developed idea of inertia - objects stay in motion if no friction
experimented - objects fall at constant speed
contradicted aristotle

114
Q

Newton

A

3 Laws of motion
inertia
force
equal and opposite

115
Q

Newton’s Gravity

A

gravitational force between two masses

116
Q

Emmy Noether - 1920s

A

showed conservation laws result from symmetries in nature
translation - momentum conservation
rotation - angular momentum conservation
time zero point - energy conservation

117
Q

Galileo’s observations

A

moon has mountains
jupiter has 4 moons
sun has blemishes
more stars than we can see
venus has phases like the moon - shows orbit

118
Q

telescopes two things

A

resolution - makes things appear larger so you can see more detail
gather light - make things
brighter/ see more things

119
Q

How does light move?

A

as a wave that caries energy

120
Q

Resolution

A

increases with larger diameter limited by the atmosphere

121
Q

light gathering power

A

depends on the light collecting area - aperture squared

122
Q

refracting telescope

A

lens focuses light onto the focal plane
causes chromatic aberration where wavelengths are focused at different focal lengths
difficult and expensive
no benefits

123
Q

reflecting telescope

A

concave mirror focuses light onto the focal plane
most are

124
Q

modern telescope engineering improvements

A

bigger

125
Q

Atmospheric turbulence

A

causes the twinkle of stars
wind blows the density variations, varying index of refraction bends the incoming light

126
Q

radio telescopes

A

uses radio waves

127
Q

adaptive optics

A

use fast cameras to correct for atmospheric blur

128
Q

spectroscopy

A

measure the temperature of the source
measure the elemental composition of the source
measure the velocity of the source

129
Q

emission lines

A

each element has its own set of electron energy levels that emit light at a particular wavelength

130
Q

three kinds of spectra

A

continuous - no breaks
absorption lines ever
absorption spectrum - the colors that are absorbed
emission spectrum - the colors that aren’t absorbed

131
Q

electrons movement

A

both waves and particles
because wave can only have specific wavelengths - causes the spectra

132
Q

blackbody radiation

A

thermal radiation
the temperature of atoms in a box measures the average speed of each atom
the spectrum varies with temperature
happens cause the light is a particle

133
Q

peak of blackbody wien law

A

the peak of the black body spectrum shifts towards shorter wavelengths when the temperature increases
the hotter the bluer

134
Q

total energy of a blackbody

A

the lumosity
temperature to the 4th power

135
Q

doppler effect

A

the wave of a moving object decreases in wavelength

136
Q

radial velocity measurement

A

the doppler shift can be used, only for radial velocity not true velocity

Astronomy (2 decks)

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