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

The electromagnetic Spectrum

(figure 5.6 from textbook)

Fig 7.5 (from text)

700nm 400nm

Wavelength (meters)

410 1410 810 1210 1610

Radio InfraredUltraviolet

X-raysGamma

rays

310 7101110 1510 1910 2310

1210 810 410 1 410 810

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

EmitterObserver

Relative speed v

Emitted wavelength

0

shift restrad

rest

v

c

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 SpectrumLyman- peak

Quasar spectrum

Suppressed Quasar spectrum

Lyman- 1216

(1 )

(1 5.8) 1216

8269

shfted z

0 5.8z