Astronomy unit 3 - EM Spectrum and light

The Electromagnetic Spectrum let us

discover regions beyond the visible universe

What is same for all electromagnetic waves?

speed due to the vacuum of space

Atmospheric windows are made of

visible, radio, UV, and Infrared rays

Interactions of Radiation & Matter

• Reflection, refraction, transmission, scattering, absorption, emission

Thermal Radiation

The Kelvin Temperature Scale & Radiation (Laws Planck equations Wien's Law Stefan-Boltzmann Law)

Waves can

transfer energy and information from one place to another

Period

time between passage of successive crests

Mechanical waves

water waves, sound waves, and so on, must travel in a medium

EM waves are created by

accelerating charged particles

The wave nature of radiation:

radiation can diffract and interfere, which are purely wave phenomena

Who tested "The wave nature of radiation"

Young's double slit experiment

William Herschel (1800)

Infrared & Ultraviolet

Heinrich Hertz (1887-8)

radio waves

Wilhelm Roentgen (1895)

x-rays

Ernest Rutherford (1900)

gamma (γ) rays

Cleeton & Williams (1933)

microwaves

order of EM spectrum

R M I V U X G

Space astronomy began with

Sputnik I in 1957 (all regions)

All thermal motion (in Kelvin) ceases at

0K

Water freezes at

273 K

Water boils at

373 K

Thermal (Blackbody) Radiation

radiation emitted by an object depending only on its temperature

Wien's Law:

Peak wavelength is inversely proportional to temperature

Radiation Laws

Total energy emitted is proportional to fourth power of temperature (note intensity-the area under the curves)

The Doppler Effect definition

If one is moving toward a source of radiation, the wavelengths seem shorter; if moving away, they seem longer

Doppler effect depends...

only on the relative motion of source and observer

Doppler effect can be used to

determine speeds of rotation, stellar and galactic motions, detect extrasolar planets and more (or radial motion)