astronomy test 5/6

Electromagnetic radiation (EMR)

Energy that travels through space as waves with electric and magnetic components

Electromagnetic spectrum

The full range of electromagnetic radiation from longest to shortest wavelengths

Speed of light

3.0 × 10⁸ m/s; all electromagnetic radiation travels at this speed in a vacuum

Wavelength

The distance between peaks of a wave; determines color and energy

Energy vs wavelength

Shorter wavelength = higher energy; longer wavelength = lower energy

Order of EM spectrum

Radio → Microwave → Infrared → Visible → Ultraviolet → X

Radio waves

Longest wavelength EMR; used in communication (phones, radio)

Microwaves

Used to heat food by exciting water molecules

Infrared

Heat radiation; used in remotes and thermal imaging

Visible light

Only portion of EMR humans can see

Ultraviolet

Causes tanning and sunburn; can damage DNA

Gamma rays

Highest energy EMR; used to kill cancer cells

Visible light order

Red → Orange → Yellow → Green → Blue → Violet

Red light

Longest wavelength (~700 nm), lowest energy

Violet light

Shortest wavelength (~400 nm), highest energy

Thermal energy

Energy from motion of particles in matter

Kinetic energy

Energy of motion; faster particles = more energy

Temperature and particles

Hotter = particles move faster and collide more

Blackbody

An ideal object that absorbs and emits all radiation perfectly

Blackbody curve

Graph showing intensity of radiation vs wavelength for an object

Wien’s Law

Hotter objects emit shorter wavelengths (bluer); cooler objects emit longer wavelengths (redder)

Wien’s Law relationship

Temperature is inversely proportional to peak wavelength

Stefan-Boltzmann Law

Total energy emitted increases rapidly with temperature (T⁴)

Hot vs cool objects

Hot = brighter and bluer; cool = dimmer and redder

Peak wavelength shift

As temperature increases, peak shifts to shorter wavelengths

Energy output

As temperature increases, total energy emitted increases at all wavelengths

Continuous spectrum

Full rainbow; produced by hot dense objects

Emission spectrum

Bright lines; produced by hot, low density gas

Absorption spectrum

Dark lines in a rainbow; produced when light passes through cooler gas

Kirchhoff’s Law 1

Hot dense object produces a continuous spectrum

Kirchhoff’s Law 2

Hot gas produces an emission line spectrum

Kirchhoff’s Law 3

Cool gas in front of a light source produces an absorption spectrum

Spectral lines

Unique patterns of light produced by elements

Why spectral lines form

Electrons jump between energy levels and emit/absorb specific wavelengths

Spectroscopy

Study of light to determine composition of objects

How we know star composition

Match spectral lines to known elements

Why the Sun has absorption lines

Light passes through cooler gas in its atmosphere

Doppler shift

Change in wavelength due to motion of source

Redshift

Object moving away; wavelength increases

Blueshift

Object moving toward; wavelength decreases

What Doppler shift tells us

Speed and direction of an object along our line of sight

Doppler effect cause

Relative motion between source and observer

Does light actually change color?

Not visibly; shift is measured, not dramatically seen

Stars as blackbodies

Stars behave approximately like blackbodies

What Wien’s Law tells us

Temperature of a star

What Stefan-Boltzmann tells us

Temperature of a star

What spectral lines tell us

Chemical composition

What Doppler shift tells us

Motion of stars/galaxies