5.2 Electromagnetic Spectrum

Continuous Spectrum:

• All electromagnetic wavelengths on the spectrum → forming blackbody radiation (ideal/perfect)

Ultraviolet catastrophe

• nfinitely large intensity as wavelengths became smaller → until explained by Max Planck

Radiowave

• Anything longer than a microwave

  • AM radio waves are absorbed and reflected by the Earth's Ionosphere (a layer of charged particles at the very top of the atmosphere)

  • More supernova remnants

• Microwave (1 millimeter to 1 meter): 

• Good for heating foods - Absorbed by water vapor 

• Active galaxies, cosmic background radiation

• IR Radiation: 780 nm to 1 mm (1,000,000 nm)

• From cool clouds of dust, planets and moons

• Visible light is from 380-750nm

• Light humans can perceive

• From stars 

UVA (400–315 nm), UVB (315–280 nm) and UVC (280–100 nm)

• blocked out by the ozone

  • AKA blacklight 

  • Hot stars and supernova remnants

X-rays(20nm-0.01nm)

• Energetic enough to penetrate soft tissues but not bones → hence allowing for imaging 

  • Gas in clusters of galaxies, supernova remnants, solar corona

• Gamma radiation

• Smaller wavelengths than UV and X-rays → Very dangerous for living tissue 

  • Absorbed through our atmosphere 

• Generated from the interior of stars, merging of stellar corpses and the death of stars

Line Spectra

•  a series of discrete, narrow lines of specific wavelengths produced by a light source or absorbing medium → Two types of line spectra

1. Emission Spectrum

2. Absorption spectrum

Emission Spectrum

Produced when an excited atom or ion drops down to a lower energy level and releases energy as photons of light.

Absorption spectrum

Produced when atoms in the ground state absorb photons of specific energies to move electrons to higher energy levels

Temperature

• etermines the type of electromagnetic radiation emitted by the sun, starts and other astronomical objects 

  • → hotter the matter the more rapid the motion

  • Kelvin: Measurement of temperature, where 0 ceases any motion 

    • 273K = 0^oC

Blackbody

•  Idealized object that radiates the continuous spectrum of wavelengths 

  • Also absorbs all the electromagnetic energy that falls onto it 

  • Radiates electromagnetic waves until its absorption and radiation are balanced

Power

• Energy coming off per second 

Wien's Law

•  Solves for the Wavelength at maximum power

  • • Wavelength = nm

    • Temperature = K

Energy Flux

• The power emitted per square meter

Stefan-Boltzmann Law:

That energy flux is proportional to the fourth power of its absolute temperature
F = L/4(pi)2^2

• Flux = units of watts per square meter 

• Sigma = constant number of 5.67 x10^-8

• Value does change with distance

Absolute luminosity

•  Total power emitted by a star

  • Multiplying energy flux by the surface area of a sphere gives luminosity 

  • Does not change with distance