SP200: Measuring the Universe

Measuring the Universe

Electromagnetic Radiation

Overview of Electromagnetic Radiation

  • Electromagnetic (EM) radiation consists of waves with two fundamental properties:

    • Specific Wavelength

    • Wave properties:

      • Wavelength

      • Frequency

      • Exhibits interference, diffraction, and polarization

    • Specific Energy

    • Particle properties:

      • Energy in quantum units is represented by photons.

      • Single photons can be detected by sensitive instruments.

Definition of Key Terms

  • Wavelength: The distance between successive crests of a wave, typically measured in nanometers (nm) for the visible spectrum and other relevant bands.

  • Frequency: The number of occurrences of a repeating event per unit of time, measured in Hertz (Hz).

  • Photon Energy: Energy of an electromagnetic wave is inversely proportional to its wavelength and directly proportional to its frequency.

    • Total transmitted or received energy is calculated as photon energy times intensity.

Electromagnetic Spectrum and Measurements

  • Visual representation of the electromagnetic spectrum's wavelength and energy relationships:

    • Visible Spectrum Wavelengths:

    • Ranges from 380 nm (violet) to 750 nm (red).

    • Energy-Frequency Graph:

    • Energy increases with frequency and decreases with wavelength.

Specific Frequencies and Energy Levels




  • Common Frequency Bands:


    Frequency

    Wavelength

    Energy



    300 EHZ

    1 pm

    1.24 MeV



    30 EHZ

    10 pm

    124 keV



    3 EHz

    100 pm

    12.4 keV



    300 PHz

    1 nm

    1.24 keV



    30 PHz

    10 nm

    124 eV



    3 PHz

    100 nm

    12.4 eV



    300 THz

    1 μm

    1.24 eV



    30 THz

    10 μm

    124 meV



    3 THz

    100 μm

    12.4 meV



    300 GHz

    1 mm

    1.24 meV



    30 GHz

    1 cm

    124 μeV



    3 GHz

    1 dm

    12.4 μeV



    300 MHz

    1 m

    1.24 μeV



    30 MHz

    10 m

    124 neV



    3 MHz

    100 m

    12.4 neV



    300 kHz

    1 km

    1.24 neV



    30 kHz

    10 km

    124 peV



    3 kHz

    100 km

    12.4 peV



    300 Hz

    1 Mm

    1.24 peV



    30 Hz

    10 Mm

    124 feV



    3 Hz

    100 Mm

    12.4 feV






    Wavelength and Energy Relationship




    • As the wavelength decreases, the energy level of the electromagnetic radiation increases.

    • Relationship:

      • E=himesfE = h imes f

      • Where:

      • EE is energy,

      • hh is Planck's constant, and

      • ff is frequency.

    Interaction with Materials

    • Low-energy Photons:

      • Have minimal interaction with material.

    • High-energy Photons:

      • Interact more significantly with all materials.

    • Special sensors are engineered to facilitate interaction with electromagnetic waves and photons at specific frequencies and wavelengths.

    Frequency Specific Sensors and Their Applications

    • Radio Frequencies:

      • Sensors: Metal wire antenna elements.

      • Interaction: Photons interact with the ionosphere (mostly electrons).

      • Applications: Primarily used for examining planetary atmospheres.

    • Microwave Frequencies:

      • Sensors: Metal wire antenna elements.

      • Interaction: Photons interact broadly with most materials.

      • Applications: Used for nearly all planetary, stellar, and universal observations; good for detecting hydrogen, the most abundant material in the universe.

    • Infrared Frequencies:

      • Sensors: Solid materials sensitive to IR bands (mostly crystals).

      • Interaction: IR photons have varied characteristics from far to near IR.

      • Applications: Used in many planetary and stellar observations, useful for red-shifted objects from the early universe.

    • Visible Light Frequencies:

      • Sensors: Films and solid materials sensitive in the visible band (especially semiconductors for imaging).

      • Interaction: Visible photons interact with nearly all materials differently based on specific bands.

      • Applications: Most commonly used for observing planets, stars, and the universe, sensitive to atmospheric interference.

    • Ultraviolet Frequencies:

      • Sensors: Solid materials, often crystals for spectra and imaging.

      • Interaction: UV photons interact with all materials, with near UV being the least energetic and extreme UV being the highest.

      • Applications: Used for studying planetary atmospheres, surface composition, stars, and galaxies; necessitate satellite-based telescopes due to atmospheric absorption.

    • X-ray Frequencies:

      • Sensors: Solid materials, mostly crystals for spectral and imaging applications.

      • Interaction: X-ray photons interact strongly with all materials; classified as soft (lower energy) and hard (higher energy).

      • Applications: Studied in various celestial bodies like stars and black holes, requiring satellite telescopes due to atmospheric absorption.

    • Gamma-ray Frequencies:

      • Sensors: Solid materials, primarily crystals for spectra and imaging.

      • Interaction: Gamma photons exhibit a strong interaction with materials.

      • Applications: Used for studying stars, supernovae, black holes, and galaxies, necessitating satellite placements to bypass atmospheric absorption.