Lecture 2 - Astronomy Background Flashcards
what are the 3 types of astronomical data?
- images
- time series
- spectra
- what do images show?
- when are images especially helpful?
- what is the problem with images?
- images show the static nature of light
- images are especially helpful if events are too quick for radio waves to detect
- the problem with images is that they do not show changes or evolution
what are 3 limitations of astronomical data?
- large distances
- extreme conditions –> direct samples limited to our solar system + where we can send probes, landers, and sample return missions
- must use INDIRECT PROXY MEASUREMENTS of physical properties
what 2 things do images show?
- position –> astrometry
- morphology –> structure, evolution
what do time series show?
time series show variations in the brightness of celestial signals or changes in location on the sky
what 2 things do time series measure and 1 type of thing that time series help us study?
- measure motions –> dynamics
- measure rotation –> pulsation
- help us study instabilities –> sunspots, X-ray bursts
what is a CEPHOID VARIABLE and what does it measure? what does the period tell you?
a variable star that pulsates in diameter and temperature –> i.e. lets you measure optical light intensity vs. time
the period of variation is related to a star’s luminosity which indicates the interstellar and intergalactic distance
what is radial stellar pulsation?
variation in diameter and temperature
what did Henrietta Swan Leavitt do and find?
examined photographic plates in telescope to measure + catalog star brightness
found stars and catalogued them as a function of brightness –> found DIRECT CORRELATION btwn pulsation and brightness (i.e. period and luminosity of Cephoid variables)
what did Henrietta Swan Leavitt’s discoveries allow us to do now?
determine the distance of an object based on its luminosity and period
i.e. provided a “Standard Candle” with which to measure distances of faraway distances
what is radio pulsar?
radio brightness vs time
brightness occurs in PULSES which correspond to the rotation of a neutron star
what is a neutron star? why does it pulsate via radio pulsar?
has burned out all of its fuel and is a very compact object
pulsates bc releases huge amount of energy and does 1 revolution in less than a second (v fast!)
what do spectra measure?
measures colours of objects or energy distribution of light –> indicates what is burning inside the star
what 4 things do spectra determine?
- temperature
- composition
- evolutionary state
- motion toward and away from us
how do spectra determine temperature? how do spectra determine composition?
TEMPERATURE –> by continuous spectrum
COMPOSITION –> ex. find sun composition by superimposing absorption lines on a solar continuous spectrum
all 3 types of astronomical data involve _______
all 3 types of astronomical data involve light
almost everything we know about space has involved light except: (2)
- MATTER SAMPLES (rare - lunar/martian/asteroid landers)
- NEUTRINO SAMPLES (rare - particle that barely interacts with matter but can still travel the cosmos)
what did Newton show us about white light?
Newton showed that white light is a SPECTRUM of many colours
what are the 2 natures of light?
wave AND particle (a photon)
the dual nature of light is due to:
the dual nature of light is due to quantum mechanics
describe the wave nature of light
characterized by wavelengths (distance from crest to crest)
light particles move up and down along waves but don’t carry matter with them
describe the particle nature of light
characterized by energy
vibrations of matter allow waves to transmit energy from 1 place to another even though the particles of matter do not interact
what is colour? what happens to energy if there is a shorter wavelength?
colours occur at specific wavelengths and energy
if there is a shorter wavelength, the energy is higher
what is the electromagnetic spectrum?
a range of colours with wavelengths/energies beyond what the eye can see
what is another name for light?
ELECTROMAGNETIC RADIATION
light is waves of ______ and _______
what are wavelengths a measure of?
light is waves of ELECTRIC and MAGNETIC fields
wavelengths are the distance from crest to crest of these waves
what is a field?
strength of force that a particle experiences at any point in space –> diff strengths in diff places
what is the order of lowest to greatest wavelength light? (7)
- gamma
- X-ray
- UV
- visual
- infrared
- microwave
- radio
what is the speed of light in a vacuum? what is the equation?
c = 3x10^8 m/s = frequency * wavelength
what are frequencies measured in?
1/s or Hz –> measure how fast it oscillates
compare the frequencies of wavelength = 1 and wavelength = 1/2
frequency for wavelength = 1 is HALF the frequency for wavelength = 1/2
what is the wavelength of 93.3 FM broadcasting waves with frequency = 93.3 MHz?
- 93.3 MHz = 93.3x10^6 Hz
- wavelength = (3x10^8 m/s) / (93.3x10^6 1/s) = 3.2m
what does the speed of light indicate?
how fast the peaks of waves travel i.e. how fast the energy travels
how does the speed of light change btwn colours in a vacuum?
speed of light is the same for every colour
would we expect the speed of light outside of a vacuum to be larger or smaller than c = 3x10^8 m/s?
slower outside of a vacuum bc of gases affecting the speed –> can never exceed the speed of light
how many Earth radii does light travel per second if the Earth’s radius is 6378 km?
c = 3x10^8 m/s = 3x10^5 km/s
(3x10^5 km/s) / 6378 km = 47 Earth radii per second
what is the equation for light travel time and what does it mean?
d = c*t
light takes a finite time to travel specific distances
what is the definition of a light year and what is 1 light year equal to?
a light year is the distance light travels in a year (DISTANCE NOT TIME)
1 light year = 9.4x10^15 m (determined by d = c*t, where t = 1 year)
what are the astronomical distances (in light years) of:
1. sun
2. nearest star
3. center of Milky Way
4. nearest large galaxy (M31)
5. Big Bang
- sun –> 0.000015 Lyr
- nearest star –> 4.3 Lyr
- center of Milky Way –> 26,000 Lyr
- nearest large galaxy (M31) –> 2.5 million Lyr
- Big Bang –> 13.7 billion Lyr
what is an astronomical unit? what is this in light minutes, meters, and km?
1 astronomical unit = 1 Earth-sun distance
= 8.3 light minutes
= 1.5x10^11 m
= 1.5x10^8 km
= 150 million km
describe the order of planets from the sun (closest to furthest)
- Mercury
- Venus
- Earth
- Mars
- Jupiter
- Saturn
- Uranus
- Neptune
what are 5 helpful astronomical distance units and what are they used for?
- Km –> for planet size, geographical objects on planets
- AU –> distances of objects within solar system
- Light-minutes –> distances of objects within solar system
- Light-years –> distances within + beyond Milky Way
- Parsecs –> same scale as light-years
what is a parsec?
distance from sun to an astronomical object with PARALLAX ANGLE of 1 arcsecond
what is 1 degree equal to? what is 1 arcminute equal to?
1 degree = 60 arcminutes
1 arcminute = 60 arcseconds
if an object is further away, how does the parallax angle change? and vice versa? why?
if an object is further away –> SMALLER parallax angle
if an object is closer –> LARGER parallax angle
why do nearby stars appear to move with Earth but further stars appear to be static?
if you move closer to something, the angle of its distance from you will increase
what is 1 pc equal to in Lyr, AU, and km?
1 pc = 3.26 Lyr = 206,000 AU = 30.9 trillion km
