exam 2

wave-particle duality

the theory that electromagnetic radiation (light) may be treated as either a particle or electromagnetic wave

parallax

the shift in an object’s perceived position caused by the observer’s motion. the closer something is, the bigger parallax shift it appears to have

properties of light

speed of light in empty space is constant, light is made up of electric and magnetic energy, light can travel through a vacuum

lambda

also called a wavelength, it corresponds with distance between the peaks of waves and falling nodes

frequency

1/T, how many cycles there are per second, how often is the wave going up and down?

interference

2 waves can occupy the same space

constructive interference

when 2 waves are the same and occupying the same space, they both amplify their wave together

destructive interference

when 2 waves are occupying the same space but theyre opposites, they zero each other out (a flat line)

photon

particle of light

All waves need a medium to pass through except for?

light because it is an electromagnetic wave that can pass through empty space

inverse square law

the apparent brightness of a body decreases inversely as the square of its distance. in other words, if you double the distance from a light source, the intensity of the light is reduced to ¼ of its original value

arc minute

a unit of angular size, 1/60 of a degree. 3600 arc seconds are in 1 degree

What happens to the speed of light when it travels through a material?

it becomes slower

proper motion

stars moving across our line of sight show a steady, straight-line change in position over time

What speed does light travel through empty space?

all light travels at the same speed

explain what it means for wavelength and frequency to be inversely proportional

when the wavelength is longer, the frequency is lower; when the wavelength is shorter, the frequency is higher

How do you create white light?

by mixing all the colors together

list energy rays from highest to lowest

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

telescope purpose

gathering and focusing light to see objects in more detail. larger diameter collects more light

list the longest wavelength to shortest wavelength

red, orange, green, blue, violet

What does distance do to light?

light doesnt get weaker with distance, it just spreads out, so there’s less light per area

intensity

how bright something is. total light emitted divided by area of sphere or 1/r². the further you are, the smaller the number is. to determine distance, take sq. root of how many times brighter a star is

area of a telescope

πr² = π/4 x D² doubling the size of a telescope increases the amount of light it gets by 4 times

opaque

cant see through

opacity

how much you can see through

blackbody

must be dense. theoretical object that absorbs all the radiation falling on it, reflecting no light. ideal radiator when hot and perfect absorber when cold. examples: earth, charcoal, sun

Wien’s law

as an object’s temperature rises, the object radiates light more strongly at shorter wavelengths

refraction

bending of light when it passes from 1 substance and enters another, generally with a different density. light is bent because its speed changes as it enters matter

reflector

a telescope that uses a mirror to collect and focus light. it uses a secondary mirror that blocks some of the primary mirror

resolution

ability of a telescope to discern fine details of an image

sensitivity

ability to detect low surface-brightness objects

field of view

the angular size of the sky that can be observed

interferometry

uses a ton of telescopes simultaneously, uses interference to improve resolving power. the telescopes act as opposite edges of a large telescope to achieve the equivalent of a single large aperture

atmospheric window

wavelength region in which electromagnetic energy passes through our atmosphere easily compared with other nearby wavelengths. radio and visible wavelengths can pass through, others cant so we have to put those telescopes in space

How is energy radiated?

in the form of heat

What wavelength do humans emit at?

they emit at all wavelengths but mostly at infrared

Which color is colder and which is hotter?

blue is the hottest so the hotter something gets the more it glows, and has a small wavelength since it has a higher frequency. red is the coldest, and has a large wavelength since it has a lower frequency

ionization

an electron absorbs so much energy it escapes the atom entirely

emission

a photon is emitted when an excited electron releases energy and drops to a lower energy level

absorption

energy from the absorbed photon raises the electron to a higher energy level

spectroscopy

name of technique used to capture and analyze the light from an astronomical body

spectra

a display of the intensity of light as a function of wavelength or frequency

types of spectra

continuous, emission, absorption

continuous spectrum

spectrum with neither dark absorption nor bright emission lines. the intensity of the radiation in such a spectrum changes smoothly from 1 wavelength to the next

emission spectrum

spectrum consisting of bright lines at certain wavelengths separated by darker regions in which little or no radiation is emitted

absorption spectrum

spectrum in which certain wavelengths are darker than adjacent wavelengths the missing light is absorbed by atoms or molecules between the source and the observer

What does hot dense light do in regards to spectra?

it emits a continuous spectrum

What does a slit and prism do in regards to spectra?

slit and prism selects a portion of the light and then disperses it into a spectrum

What does a cloud of cool gas do in regards to spectra?

it absorbs specific wavelengths of light passing through it, creating absorption lines

doppler shift

the frequency of a wave changes for an observer moving relative to the source of the wave. when the source of the wave moves towards the observer, the waves are compressed, leading to a higher frequency 

radial velocity

the velocity of a body along one’s line of sight (directly toward or away)

doppler broadening

widening of a spectral line caused by motions of the material producing the line both toward and away from the observer. occurs when atoms in a gas are moving at different radial velocities

blueshift

objects moving towards you

redshift

objects moving away from you

If there is no line-of-sight velocity, what type of shift is it?

there is zero shift if it is neither moving away or towards you