Midterm Flashcards
Light year
distance light travels in a year
=9.6x10^12 km about 10^13 km
Astronomical unit
AU = 1.5x10^8 km
Earth-Sun Distance
Parsec
pc = 3.1x10^13 km
about 3 lyr
nanometer
10 Angstrom
Distance of sun
8 light-minutes
Nearest Star
1 parsec = 3.3 light years
size of milky way
90000 light years
Nearest galaxy
10 million light years
Clusters of Galaxies
1 billion years = Gigayear = Gyr
Galaxies forming
10 Gyr
Cosmic Microwave Background
14 billion years
1x10^18
Exa E
1x10^15
Peta P
1x10^12
Tera T
1x10^9
Giga G
1x10^6
Mega M
1x10^3
Kilo k
1x10^-2
Centi c
1x10^-3
Milli m
1x10^-6
Micro u
1x10^-9
Nano n
1x10^-12
Pico p
1x10^-15
Femto f
1x10^-18
Atto a
Statistical (noise) uncertainty
not enough data
Systematic uncertainty
incorrect assumption
Scientific method
Prediction
Experiment to test model
Revise or keep same
Model (theory)
celestial sphere
the inverted dome you see the stars on
Zenith on celestial sphere
the point overhead
Local celestial meridian
runs from the N to S through Zenith
Altitude
the vertical angle on the celestial sphere
Azimuth
the horizontal angle from north or south
New Moon
0 days
nothing
rises at noon
sets at sunset
First Quarter
7 days
half
rises at sunset
sets at midnight
Full Moon
14 days
full
rises at midnight
sets at sunrise
Third Quarter
21 days
half
rises at sunrise
sets noon
Waxing crescent
2-6 days
Waxing gibbous
8-13 days
How far does the moon move per day?
12 deg/day
Period of the moon
4 weeks - 28 days
The phases of the moon are caused by …
the moon’s position around the Earth in relation to the sun.
Waning gibbous
15-20 days
Waning Crescent
22-27 days
Nadir
Point on the celestial sphere directly underneath
celestial equator
projection of earth’s equator onto the celestial sphere
north celestial pole
projection of earth’s north pole onto the celestial sphere
constellations
unrelated stars
only appear to be close together
Earth spins on its axis every …
~ 24 hours
Earth orbits the Sun in …
~ 365 days
Earth’s axis precesses on a …
26000 year cycle
Moon orbits Earth …
~ 28 days
Planets orbit Sun …
in a variety of of periods
Proper motion of stars
very small
less than 1 arcsec/century
degree
circle divided into 360 parts
arcminute
degree divided into 60 parts
arcsecond
arc minute divided into 60 parts
angular size
apparent angle between objects on the sky
noon is defined as …
the Sun crossing “local meridian”
One solar day
24 hours from noon to noon
the sun’s apparent path on the sky is called the …
Ecliptic
the ecliptic is also the projection of Earth’s orbit onto the celestial sphere
What does sidereal mean?
compared with the stars
Are sidereal time and Solar time the same?
no
Sidereal time is …
the time it takes for a star to come back to the same meridian
23 hours 56 minutes
Who is sidereal time good for?
astronomers
Who is solar time good for?
people
lunar eclipse
the Earth casts a shadow and the Moon can sometimes pass through it
Where can a solar eclipse be seen from?
a small area on earth
50 miles
Where can a lunar eclipse be seen from?
the entire night side of the Earth
Line of Nodes
where two orbital planes cross
When can a solar eclipse occur?
When a new moon passes a node
When can a lunar eclipse occur?
When a full moon passes a node
size of the moon and sun from earth
.5 degree
during a total solar eclipse what can you see of the sun
chromosphere and corona
Small angle formula
angle a = 206265 c d/D
d is size of object
D is distance to object
angle in arcsec
Angle of sun
32 arcmin
Angle of moon
33 arcmin
Composition of sun
ball of gas with no solid surface
Density of sun
decreases from the center out
Temperature of corona
1 million degrees
Temperature of chromosphere
10000 K
Temperature of photosphere
5800 degrees
Temperature of sunspots
slightly cooler than photosphere
Apogee
position furthest away from eath
perigee
position closest to earth
Perihelion
position closest to the sun
aphelion
position furthest away from the sun
Annular solar eclipses
happens when earth is near perihelion and moon is near apogee
see more of the sun
What does the distance change about viewing the moon and sun
angular distance varies
What causes seasons
the tilt of the earth makes the sun appear lower in winter and higher in summer
less sun = colder
Does the obliquity of earth’s orbit cause seasons
no
when does the sun’s ecliptic cross the equator
vernal equinox about mar 21
autumnal equinox about sep 23
When are the highest and lowest points of the sun
Summer solstice about June 21
winter solstice about dec 21
Celestial coordinates
position of every object defined by Ra, Dec and epoch
Precession
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
Cosmology 400 BC to 1500 AD
earth at center of the universe
planets moved in perfect circles
planets move with a constant velocity
stars just beyond saturn
Aristotle - 300 BC
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
Aristarchus - 260 BC
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
Parallax
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
Who measured mars’ parallax and when
using what
Cassini in 1673
Paris to Africa
Motion of outer plannets
not a constant rate
Ptolemy - 100 BC
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
Retrograde Motion in Geocentric Model
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
The eccentric epicycle
the earth is offset from the orbit center
the equant epicycle
constant velocity about a point not centered
Copernicus - 1500 AD
publishes a heliocentric model
explains retrograde motion
keeps perfect circles and uniform motion
Copernican Revolutions
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
Retrograde motion in heliocentric model
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
Tycho Brahe - 1570
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
Johannes Kepler - 1600
used data of Tycho to break Aristotle’s hold on universe
discovered 3 rules that describe motions of planets
Kepler’s Law #1
Planets trace out ellipses with the Sun as one focus
planet orbits are only slightly elliptical
Kepler’s Law #2
planets sweep out equal areas in equal times
planet moves faster when close to the sun than further away
Kepler’s Law #3
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
Galileo Galilee - 1600
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
Newton
3 Laws of motion
inertia
force
equal and opposite
Newton’s Gravity
gravitational force between two masses
Emmy Noether - 1920s
showed conservation laws result from symmetries in nature
translation - momentum conservation
rotation - angular momentum conservation
time zero point - energy conservation
Galileo’s observations
moon has mountains
jupiter has 4 moons
sun has blemishes
more stars than we can see
venus has phases like the moon - shows orbit
telescopes two things
resolution - makes things appear larger so you can see more detail
gather light - make things
brighter/ see more things
How does light move?
as a wave that caries energy
Resolution
increases with larger diameter limited by the atmosphere
light gathering power
depends on the light collecting area - aperture squared
refracting telescope
lens focuses light onto the focal plane
causes chromatic aberration where wavelengths are focused at different focal lengths
difficult and expensive
no benefits
reflecting telescope
concave mirror focuses light onto the focal plane
most are
modern telescope engineering improvements
bigger
Atmospheric turbulence
causes the twinkle of stars
wind blows the density variations, varying index of refraction bends the incoming light
radio telescopes
uses radio waves
adaptive optics
use fast cameras to correct for atmospheric blur
spectroscopy
measure the temperature of the source
measure the elemental composition of the source
measure the velocity of the source
emission lines
each element has its own set of electron energy levels that emit light at a particular wavelength
three kinds of spectra
continuous - no breaks
absorption lines ever
absorption spectrum - the colors that are absorbed
emission spectrum - the colors that aren’t absorbed
electrons movement
both waves and particles
because wave can only have specific wavelengths - causes the spectra
blackbody radiation
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
peak of blackbody wien law
the peak of the black body spectrum shifts towards shorter wavelengths when the temperature increases
the hotter the bluer
total energy of a blackbody
the lumosity
temperature to the 4th power
doppler effect
the wave of a moving object decreases in wavelength
radial velocity measurement
the doppler shift can be used, only for radial velocity not true velocity
