1. Measuring the Universe

2. Electromagnetic Radiation

3. Common frequency bands

4. 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

5. 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

6. Electromagnetic Radiation EM equivalent Energy-Intensity curve

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. Electromagnetic Radiation Common frequency bands