Measuring the Universe

Electromagnetic Radiation

Common frequency bands

Electromagnetic Radiation Electromagnetic waves have two basic properties   Specific wavelength Wave properties   Wavelength, frequency Exhibit interference, diffraction, and polarization   Specific energy Particle properties   Energy in quantum units = photons Single photons can be detected by sensitive instruments

Electromagnetic Radiation   Energy of electromagnetic radiation is inherent in its frequency/band   Intensity of EM radiation is measured in the number of photons   Total transmitted or received energy is the photon energy (frequency) times intensity

Electromagnetic Radiation EM equivalent Energy-Intensity curve

Electromagnetic Radiation   Low-energy photons have little interaction with material   High-energy photons interact with everything   Sensors are designed for interaction with EM waves/photons at specific frequencies/wavelengths

Electromagnetic Radiation Radio frequencies   Sensors: Metal wire antenna elements   Interaction: Photons interact with ionosphere (mostly electrons)   Observations: Radio frequencies are primarily used to examine planetary atmospheres

Electromagnetic Radiation Microwave   Sensors: Metal wire antenna elements   Interaction: Microwave band photons interact with most materials   Observations: Microwave frequencies are used for almost all planetary, stellar, and universe observations Versatile interaction with material Simple technology Extremely useful for detecting hydrogen   The most abundant material in the universe   Microwave band used for most communications

Electromagnetic Radiation Infrared   Sensors: Solid materials sensitive in the IR band Mostly crystals CCD imaging commonly used   Interaction: IR photons interact with most materials Far IR has different character than near IR   Observations: IR frequencies are used for many planetary, stellar, and universe observations Planetary observations common (warm) Useful for measure large red-shifted objects formed in the early universe Difficult to observe through the atmosphere

Electromagnetic Radiation Visible   Sensors: Films, solid materials sensitive in visible band Semiconductors commonly used for imaging CCD imaging usually most sensitive   Interaction: Visible photons interact with almost all materials Different visible bands interact differently with most materials   Observations: Visible band is the most commonly used for planets, stars, and universe Useful since our eyes are sensitive only to that band Some interference from the atmosphere

Electromagnetic Radiation Ultraviolet   Sensors: Solid materials   Crystals commonly used for spectra and imaging CCD imaging available   Interaction: UV photons interact with all materials Near UV – least energetic Extreme UV – highest energy   Observations: UV used for planetary atmospheres and planetary/moon surface composition, stars, and galaxies UV technology difficult Completely absorbed by the atmosphere   Telescopes must be placed on satellites

Electromagnetic Radiation X-ray   Sensors: Solid materials Mostly crystals Spectra and imaging CCD imaging available   Interaction: X-ray photons interact strongly with all materials Soft X-ray – lower energies Hard X-rays – higher energies   Observations: X-ray used to study stars, supernova, black holes, and galaxies X-ray technology difficult Completely absorbed by the atmosphere   Telescopes must be placed on satellites

Electromagnetic Radiation γ-ray   Sensors: Solid materials Mostly crystals Spectra and imaging CCD imaging available   Interaction: γ-ray photons interact very strongly with all materials   Observations: γ -ray used to study some stars, supernova, black holes, and galaxies γ -ray technology difficult Completely absorbed by the atmosphere   Telescopes must be placed on satellites

Electromagnetic Radiation Common frequency bands