Note to students: Figure numbers (from the textbook) are not up-to-date here for the 6 th edition. But you should be able to recognize the figures anyway.

The electromagnetic Spectrum (figure 5.6 from textbook) Fig 7.5 (from text) 700nm400nm Wavelength (meters) RadioInfrared Ultraviolet X-rays Gamma rays Frequency (hertz) Energy (electron volts)

Fig 5.4(from textbook)

Fig 5.5 (from textbook) Light is made up of waves in electric and magnetic fields: “electromagnetic radiation”

Fig 5.8 Changes in atomic energy levels create light particles with corresponding energies. Atomic energy levels Emission Absorption

Fig 5.9 (from text): Emission spectra for different elements Neon Sodium Helium

Fig 5.7 from textbook Schematic spectrum from a distant object.

Figure 5.13 (scanned)

Figure 5.13 (file)

The Doppler shift Emitter Observer Relative speed v Emitted wavelength Increases when receding (“redshift”) Decreases when approaching (“blueshift”)

The Cosmic Microwave Background Dipole: an illustration of the Doppler shift As we view the “edge of the observable universe” one part looks more blue than the other (by about one part in 1,000). This is successfully interpreted as the red/blue-shifting due to our motion in with respect to the frame in which the sky is homogeneous. The sky with our motion subtracted out (fluctuations at 1 part in 100,000)

Rotation of galaxy NGC 5746

Spectral lines viewed through diffraction grating Redshift Blueshift Observing Galactic Rotation

The result: A rotation curve NB, there is an overall net redshift due the the cosmic expansion.

Telescopes and the atmosphere (Fig 7.20)

Sloan Survey Image of Candidate (originally thought to be a galaxy). This image motivated Becker and colleagues to take a spectrum of this object. Hydrogen exists in space at all redshifts between us and the quasar( ). Red-shifted Lyman-  absorption from the hydrogen in this redshift range suppresses quasar light at the corresponding wavelengths. At the quasar location there is a “Lyman-  peak” due to the recombination of hydrogen that was ionized by energy from the quasar. The Spectrum Lyma n-  peak Quasar spectru m Suppressed Quasar spectrum