3.1 Cosmic Distance Ladder

From these methods: Determine distance (see p 615 including Fig 20.16)

From these methods: Determine distance (see p 626 including Fig 20.16)

From these methods: Determine distance (see p 626 including Fig 20.16)

Given luminosity infer distance (see p 626 including Fig 20.16)

Use surface temperature of “main sequence stars” to infer Luminosity.

Use pulsation period of variable starts (“Cepheids”) to infer luminosity

Given luminosity infer distance (see p 626 including Fig 20.16)

Given luminosity infer distance (see p 626 including Fig 20.16)

Use “Tully-Fisher relation” to infer galaxy luminosity from rotation speed

Given luminosity infer distance (see p 626 including Fig 20.16)

Use “Tully-Fisher relation” to infer galaxy luminosity from rotation speed

From these methods: Determine distance (see p 641)

3.2 The Redshift

Fig 20.15A redshifted galaxy spectrum

observed rest

rest

z

Redshift:

For small z v c z

3.3 The Hubble law

Putting together info about speed v and distance d reveals

remarkably simple behavior:

0v H d

0 65H Km/Sec/Megaparsec

1 Megaparsec = 3.3 million lightyears

Special feature of the Hubble law: It looks the same from any position:

The Big Bang