Astronomy & Cosmology Chap 2 : Waves and the nature of light

Emission

the object emits light on its own and that light reaches our eyes

Reflection

Light from a source bounces off the object and then reaches our eyes

Emitted lights

holds a lot of "secret" information about the object that emitted the light

Astronomical distances

looking farther away = looking more into the past

1 light year away

light takes 1 year to reach us

Sun

8 light minutes away

Sir Issac Newton

Passed sunlight through a prism 300 years ago

Band of rainbow

comes out the other side

White light Spectrum

composed all the other colors

Continuous spectrum

no colors missing

Graph of Brightness vs color

spectrum

Spectrum of white light

the colors of the optical spectrum

Wave

Regular disturbance that travels at a constant speed through a medium or material

Waves types

Waves on a guitar string, sound waves, water waves, light waves, waves on a rope

Waves properties

wavelength (λ), frequency (f), wave speed (v), amplitude (A)

Frequency (F)

how often the waves "waves". how often the source of the wave produces a bump. Measured in numbers per seconds or Hertz (Hz)

Wavelength (λ)

the distance between each subsequent bump. Measured in meters (m)

Speed (V)

Speed of the wave or how fast the wave travels forward

v = f λ

v

fixed for light in a particular material

Amplitude (A)

how big the wave is or how tall a crest or bump is

light is unusual

does not need a medium or material to travel

electromagnetic wave

combination of strengthening and weakening electric and magnetic fields.

light speed

c = 3.0 x 10^8 m/s

higher frequency (f) light

bluer has shorter wavelength

lower frequency (f) light

redder has longer wavelength

larger amplitude (A)

a brighter light

smaller amplitude (A)

a dimmer light

electromagnetic spectrum

different wavelengths of light together

optical/ visible part

this is the part of the spectrum our eyes can see.

the wavelength is from 400nm to 700nm

short wavelengths -> long wavelength

gamma ray, xrays, ultraviolet, infrared, microwaves, radio waves

newton's explanation

light is made up of corpuscles (particles) of different energies for different colors.

duality of light

light behaves both as a wave and a particle depending on the situation

photons

composed of many tiny massless particles

photon has

some amount of energy

shorter wavelengths (photons)

higher energy photons (bluer)

longer wavelengths (photons)

lower energy per photon (redder)

therefore shorter wavelengths (photons)

more energetic and damaging

high energy photon

blue light

lower energy photon

red light

low energy photon

infrared light

should be invisible

energy of a photon equation

h f = h c / λ

energy of a photon

h = planck's constant (a fixed number)

f = frequency

c = speed of light

λ = wavelength

higher frequency (shorter wavelength)

more energy in each photon

lower frequency (longer wavelength)

less energy in each photon

light properties

both particle and a wave

Quantum Theory

the branch of physics that explains how matter and energy behave at the smallest, subatomic levels

observing celestial objects

give us much more information that just observing in a single wavelength

specialized telescopes and sensors

built to collect light of different wavelengths

body that is producing the light

1. the temperature of the body

2. the chemical composition of the body

3. the speed at which the body is moving towards or away from us

what does the atmosphere let through

acts like a large filter. doesn't let different wavelengths of EM radiation though equally

temperature scales

fahrenheit, celsius, kelvin

absolute zero, 0 K

lowest possible temperature (273° C or -459°F)

fahrenheit

how humans feel temperature

celsius

how water feels temperature

kelvin

how the universe feels temperature