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Read: Chaps 19, 20 11/13/14 – slide 1
A100–Exploring the Universe: Discovering Galaxies
Martin D. Weinberg
UMass Astronomy
November 13, 2014
Announcements
⊲ Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 2
Exam #2 questions returned after class today
Solutions posted on the website in the “exams” tab. See
http://courses.umass.edu/astron100-mdw
Announcements
⊲ Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 2
Exam #2 questions returned after class today
Solutions posted on the website in the “exams” tab. See
http://courses.umass.edu/astron100-mdw
Begin by reviewing top 4 low-scoring exam questions
Today: Galaxies
⊲ What are the three major types of galaxies?
⊲ How are galaxies grouped together?
⊲ How do we determine distances to galaxies?
Announcements
⊲ Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 2
Exam #2 questions returned after class today
Solutions posted on the website in the “exams” tab. See
http://courses.umass.edu/astron100-mdw
Begin by reviewing top 4 low-scoring exam questions
Today: Galaxies
⊲ What are the three major types of galaxies?
⊲ How are galaxies grouped together?
⊲ How do we determine distances to galaxies?
Your questions?
Discussion of exam questions: #39
Announcements
⊲ Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 3
Degeneracy pressure is the source of the pressure that stops
the crush of gravity in all of the following except
(A) a brown dwarf.
(B) a neutron star.
(C) the central core of the Sun after hydrogen fusion ceases
but before helium fusion begions.
(D) a very massive main-sequence star.
(E) a white dwarf.
Discussion of exam questions: #24
Announcements
⊲ Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 4
Which of the following characteristics of stars has the greatest
range in values?
(A) surface temperature
(B) luminosity
(C) mass
(D) radius
(E) core temperature
Discussion of exam questions: #29
Announcements
⊲ Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 5
Which cluster is 10 billion years old?
Discussion of exam questions: #41
Announcements
⊲ Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 6
What is the ultimate fate of an isolated white dwarf?
(A) The electron degeneracy pressure will eventually
overwhelm gravity and the white dwarf will slowly
evaporate.
(B) As gravity overwhelms the electron degeneracy pressure,
it will explode as a supernova.
(C) It will cool down and become a cold black dwarf.
(D) As gravity overwhelms the electron degeneracy pressure,
it will explode as a nova.
(E) As gravity overwhelms the electron degeneracy pressure,
it will become a neutron star.
Galaxies!
Announcements
Exam questions
⊲ Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 7
Hubble Deep Field
Announcements
Exam questions
Galaxies!
⊲Hubble DeepField
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 8
Our deepest images of the universe show a great variety
of galaxies, some of them billions of light-years away
Galaxies and Cosmology
Read: Chaps 19, 20 11/13/14 – slide 9
A galaxys age, its distance,
and the age of the universe
are all closely related
The study of galaxies is
thus intimately connected
with cosmology—the study
of the structure and evolu-
tion of the universe
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 10
Hub-
ble
Ultra
Deep
Field
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 10
Hub-
ble
Ultra
Deep
Field
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 10
Hub-
ble
Ultra
Deep
Field
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 10
Hub-
ble
Ultra
Deep
Field
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 11
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 12
Disk Component: stars
of all ages, many gas
clouds
Spheroidal Compo-
nent: bulge & halo, old
stars, few gas clouds
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 13
Disk Compo-
nent: stars of
all ages, many
gas clouds
Spheroidal
Component:
bulge & halo,
old stars, few
gas clouds
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 13
Disk Compo-
nent: stars of
all ages, many
gas clouds
Spheroidal
Component:
bulge & halo,
old stars, few
gas clouds
Three Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
⊲Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 13
Disk Compo-
nent: stars of
all ages, many
gas clouds
Spheroidal
Component:
bulge & halo,
old stars, few
gas clouds
Thought question
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
⊲ Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 14
Why does ongoing star formation lead to a blue-white
appearance?
(A) There aren’t any red or yellow stars
(B) Short-lived blue stars outshine others
(C) Gas in the disk scatters blue light
Thought question
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
⊲ Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 14
Why does ongoing star formation lead to a blue-white
appearance?
(A) There aren’t any red or yellow stars
(B) Short-lived blue stars outshine others
(C) Gas in the disk scatters blue light
Other Types Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
⊲ Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 15
Barred Spiral Galaxy: Has a bar of stars across the bulge
Other Types of Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
⊲ Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 16
Lenticular
Galaxy: Has
a disk like a
spiral galaxy
but much less
dusty gas (in-
termediate
between spiral
and elliptical)
Elliptical Galaxies
Read: Chaps 19, 20 11/13/14 – slide 17
Elliptical Galaxy:
All spheroidal
component, vir-
tually no disk
component
Elliptical Galaxies
Read: Chaps 19, 20 11/13/14 – slide 17
Elliptical Galaxy:
All spheroidal
component, vir-
tually no disk
component
Red-yellow color
indicates older
star population
Irregular Galaxies
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
⊲ Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 18
Large Magellanic Cloud
Irregular Galaxies
Read: Chaps 19, 20 11/13/14 – slide 19
Large Magellanic CloudBlue-white color indicates ongoing
star formation
Hubble’s Galaxy Types
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
⊲Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 20
Spheroid dominates Disk Dominates
How are galaxies grouped together?
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
⊲Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 21
Groups
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
⊲ Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 22
Spiral galaxies
are often found in
groups of galaxies
(up to a few dozen
galaxies)
Clusters
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
⊲ Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 23
Elliptical galax-
ies are much
more common in
huge clusters of
galaxies
(hundreds to thou-
sands of galaxies)
Galaxies: summary
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
⊲Galaxies:summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 24
How are the lives of galaxies connected with the history
of the universe?
⊲ Galaxies generally formed when the universe was
young and have aged along with the universe
What are the three major types of galaxies?
⊲ Spiral galaxies, elliptical galaxies, and irregular
galaxies
⊲ Spirals have both disk and spheroidal components;
ellipticals have no disk
How are galaxies grouped together?
⊲ Spiral galaxies tend to collect into groups of up to a
few dozen galaxies
⊲ Elliptical galaxies are more common in large clusters
containing hundreds to thousands of galaxies
Measuring distances to galaxies
Read: Chaps 19, 20 11/13/14 – slide 25
Measuring distances to galaxies
Read: Chaps 19, 20 11/13/14 – slide 25
The Distance Ladder
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
⊲The DistanceLadder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 26
Step 1: Measure the So-
lar System by RADAR to
determine the Astronom-
ical Unit
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
⊲The DistanceLadder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 27
Step 2: Determine dis-
tances of stars out to a
few hundred light-years
using parallax
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
⊲The DistanceLadder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 28
Luminosity passing
through each sphere is
the same
Area of sphere:
4π(radius)2
Divide luminosity by
area to get brightness
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
⊲The DistanceLadder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 29
The relationship between apparent brightness and luminosity
depends on distance:
Brightness =Luminosity
4π(distance)2
We can determine a stars distance if we know its luminosity
and can measure its apparent brightness:
distance =
√
Luminosity
4πBrightness
A standard candle is an object whose luminosity we can
determine without measuring its distance
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
⊲The DistanceLadder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 30
Step 3: Apparent
brightness of star
clusters main se-
quence tells us its
distance
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
⊲The DistanceLadder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 31
Knowing a star clusters distance, we can determine the
luminosity of each type of star within it
Thought question
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
⊲ Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 32
Which kind of stars are best for measuring large distances?
(A) High-luminosity stars
(B) Low-luminosity stars
Thought question
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
⊲ Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 32
Which kind of stars are best for measuring large distances?
(A) High-luminosity stars
(B) Low-luminosity stars
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
⊲ Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 33
Step 4
Cepheid variable
stars are very
luminous
Because the period
of a Cepheid vari-
able star tells us its
luminosity, we can
use these stars as
standard candles
Cepheid Period-Luminosity relation
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
⊲ Cepheid PL
Type Ia Supernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 34
Cepheid variable stars with longer periods have greater
luminosities
Type Ia Supernova
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
⊲Type IaSupernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 35
White-dwarf supernovae can also be used as standard candles
The Distance Ladder
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
⊲Type IaSupernova
Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 36
Step 5
Apparent brightness of
white-dwarf supernova
tells us the distance to
its galaxy
(up to 10 billion light-
years)
Tully-Fisher relation
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
⊲ Tully-Fisher
Summary
Read: Chaps 19, 20 11/13/14 – slide 37
Entire galaxies can also
be used as standard can-
dles because galaxy lu-
minosity is related to ro-
tation speed
The Distance Ladder: Summary
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
⊲ Summary
Read: Chaps 19, 20 11/13/14 – slide 38
We measure galaxy distances using
a chain of interdependent
techniques
The Distance Ladder: Summary
Announcements
Exam questions
Galaxies!
Hubble Deep Field
Galaxies andCosmology
Three Types ofGalaxies
Thought question
Other types
Elliptical Galaxies
Irregular Galaxies
Hubble’s GalaxyTypes
Groups
Clusters
Galaxies: summary
Measuring distances
The Distance Ladder
Thought question
Cepheid PL
Type Ia Supernova
Tully-Fisher
⊲ Summary
Read: Chaps 19, 20 11/13/14 – slide 39
The distance-measurement chain begins with parallax
measurements that build on radar ranging in our solar
system
Using parallax and the relationship between luminosity,
distance, and brightness, we can calibrate a series of
standard candles
We can measure distances greater than 10 billion light
years using white dwarf supernovae as standard candles
