View
2
Download
0
Category
Preview:
Citation preview
Read: Chaps 20, 21 11/18/14 – slide 1
A100–Exploring the Universe: Measuring the Universe
Martin D. Weinberg
UMass Astronomy
weinberg@astro.umass.edu
November 18, 2014
Announcements
⊲ Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 2
Exam #2 scores posted in Mastering. See class web site
for answer key.
⊲ See TAs after class today for exams
Announcements
⊲ Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 2
Exam #2 scores posted in Mastering. See class web site
for answer key.
⊲ See TAs after class today for exams
Galaxies
⊲ How did Hubble prove that galaxies lie far beyond
the Milky Way?
⊲ What is Hubble’s Law?
⊲ How do distance measurements tell us the age of
the Universe?
⊲ How does the universe’s expansion affect our
distance measurements?
Announcements
⊲ Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 2
Exam #2 scores posted in Mastering. See class web site
for answer key.
⊲ See TAs after class today for exams
Galaxies
⊲ How did Hubble prove that galaxies lie far beyond
the Milky Way?
⊲ What is Hubble’s Law?
⊲ How do distance measurements tell us the age of
the Universe?
⊲ How does the universe’s expansion affect our
distance measurements?
Your questions?
Measuring distances to galaxies
Read: Chaps 20, 21 11/18/14 – slide 3
Measuring distances to galaxies
Read: Chaps 20, 21 11/18/14 – slide 3
The Distance Ladder
Tully-Fisher relation
Announcements
Measuring distances
⊲ Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 4
Entire galaxies can also
be used as standard can-
dles because galaxy lu-
minosity is related to ro-
tation speed
3 types of astronomical distance measurements
Announcements
Measuring distances
Tully-Fisher
⊲ 3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 5
1. Direct mesurements: Measuring the distance directly.
Example:
Radar
“Time of flight”
2. Standard rulers: Size = Distance × θ (angle on the sky).
Need to know the true size of the object.
Expanding supernova remnants
3. Standard candles: Lapparent = Ltrue/D2.
Need to know the true luminosity of an object.
Main-sequence fitting
Tully-Fisher
Cepheid variables
The Distance Ladder: Summary
Announcements
Measuring distances
Tully-Fisher
3 types
⊲ Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 6
We measure galaxy distances using
a chain of interdependent
techniques
The Distance Ladder: Summary
Announcements
Measuring distances
Tully-Fisher
3 types
⊲ Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 7
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
The Distance Ladder: Summary
Announcements
Measuring distances
Tully-Fisher
3 types
⊲ Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 8
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
The “Puzzle” of Spiral Nebulae
Read: Chaps 20, 21 11/18/14 – slide 9
Before Hubble, some scientists argued
that spiral nebulae were entire galaxies
like our Milky Way, while others main-
tained they were smaller collections of
stars within the Milky Way
The debate remained unsettled until
someone finally measured their dis-
tances
Physical nature of “cloudy objects” debated
Read: Chaps 20, 21 11/18/14 – slide 10
Rosse’s sketch
Lord Rosse (Irish nobleman) observed M51 with 72 inch mirror
Physical nature of “cloudy objects” debated
Read: Chaps 20, 21 11/18/14 – slide 10
Artist’s conception
Lord Rosse (Irish nobleman) observed M51 with 72 inch mirror
How it appeared to naked eye in early telescopes
Physical nature of “cloudy objects” debated
Read: Chaps 20, 21 11/18/14 – slide 10
Hubble Space Telecope
Lord Rosse (Irish nobleman) observed M51 with 72 inch mirror
How it appeared to naked eye in early telescopes
How it appears with the Hubble Space Telescope
The “Puzzle” of Spiral Nebulae
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
⊲ Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 11
Hubble settled the debate by measuring the distance to the
Andromeda Galaxy using Cepheid variables as standard
candles (late 1920’s. . . )
Hubble’s Law
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
⊲ Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 12
The spectral features of virtually all galaxies are
redshifted . . . they are all moving away from us!
Hubble’s Law
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
⊲ Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 12
The spectral features of virtually all galaxies are
redshifted . . . they are all moving away from us!
By measuring distances to galaxies, Hubble found that
redshift and distance are related in a special way
Hubble’s Measurement
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
⊲Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 13
Edwin Hubble (1929) measured distances to 25 galaxies
⊲ Distances from Cepheid variables
⊲ Velocities from redshift of spectral lines:
z =v
c=
λ− λ0
λ0
=∆λ
λ0
⊲ v = c× z = cz
He found:
recession velocity increases linearly with distance!
Hubble’s Measurement
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
⊲Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 14
How to really do it . . .
Hubble’s Measurement
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
⊲Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 14
How to really do it . . .
Spectra of cooler stars show very strong absorption lines due
to singly-ionized calcium:
Hubble’s Measurement
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
⊲Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 14
How to really do it . . .
Spectra of cooler stars show very strong absorption lines due
to singly-ionized calcium:
H K
These strong absoption line stand out in the spectrum!
Hubble’s Measurement
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
⊲Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 15
Hubble’s Measurement
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
⊲Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 15
Hubble’s Measurement
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
⊲Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 15
v = Hod Ho = 70 km/s/Mpc
New distance indicator: d = zc/Ho
Example:
Redshift of a galaxy is z = 0.1
Recession velocity: v = zc = 30, 000 km/s
Distance:
d =zc
Ho
=30, 000 km/s
70 km/s/Mpc= 429Mpc
Hubble’s Law
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
⊲ Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 16
Hubble’s Law: velocity = H0 × distance
Hubble’s Law
Read: Chaps 20, 21 11/18/14 – slide 17
Redshift of a galaxy tells us
its distance through
Hubble’s Law:
distance =velocity
H0
=zc
H0
Hubble’s Law
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
⊲ Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 18
Hubble
Ultra Deep Field
Distances of farthest galaxies are measured from redshifts
Age of the Universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
⊲Age of theUniverse
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 19
How do distance measurements tell us
the age of the Universe?
Thought question
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
⊲Age of theUniverse
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 20
Your friend leaves your house. She later calls you on her cell
phone, saying that she’s been driving at 60 miles an hour
directly away from you the whole time and is now 60 miles
away. How long has she been gone?
(A) 1 minute
(B) 30 minutes
(C) 60 minutes
(D) 120 minutes
Thought question
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
⊲Age of theUniverse
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 20
Your friend leaves your house. She later calls you on her cell
phone, saying that she’s been driving at 60 miles an hour
directly away from you the whole time and is now 60 miles
away. How long has she been gone?
(A) 1 minute
(B) 30 minutes
(C) 60 minutes
(D) 120 minutes
Expansion of the Universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
⊲Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 21
Observations suggest:
1. The expansion rate appears to be the same everywhere!
2. The Universe has no center and no boundary!
(as far as we can tell)
Expansion of the Universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
⊲Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 22
One example of something that expands but has no center or
edge is the surface of a balloon
The Cosmological Principle
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 23
The Universe looks about the same no matter
where you are within it
Matter is evenly distributed on very large scales in the
Universe
There is NO center and no edges
Not proved but consistent with all observations to date
Expansion of the Universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 24
Philosphically consistent with the lessons learned from
Ptolemy to Copernicus
⊲ We don’t want to make the same mistake again!
Expansion of the Universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 24
Philosphically consistent with the lessons learned from
Ptolemy to Copernicus
⊲ We don’t want to make the same mistake again!
Copernican view: nothing special about Earth’s position
in the Universe
Expansion of the Universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 24
Philosphically consistent with the lessons learned from
Ptolemy to Copernicus
⊲ We don’t want to make the same mistake again!
Copernican view: nothing special about Earth’s position
in the Universe
This is often called the Copernican Principle
The Cosmological Principle
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 25
Observations support the idea that the Universe is both
isotropic and homogeneous
Homogeneous: At large scales, the Universe looks the
same everywhere
⊲ There is no preferred location
⊲ I.e. no center
Isotropic: At large scales, the Universe looks the same in
all directions on the sky
⊲ There is no special direction
⊲ I.e. no axis
The Cosmological Principle
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 26
Homogeneous– looks the same independent of location
Isotropic– looks the same independent of direction
In 3 dimensions In 2 dimensions
The Cosmological Principle
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 27
Isotropy and homogeneity are related:
Isotropy +Copernican
Principle=⇒ Homogeneity
⇓
Isotropy +Isotropy around
another point=⇒ Homogeneity
The Cosmological Principle
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 28
The universe is homogeneous
and isotropic when viewed on a
large enough scale.
The Cosmological Principle derives from the Copernican
Principle
But not demanded by any physical model
It can not be proven in a mathematical sense
However:
⊲ Supported by numerous observations
⊲ Great weight from purely empirical grounds
The Cosmological Principle: Newton’s version
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 29
To prevent one part of the Universe from collapsing
(i.e. into a black hole)
⊲ Homogeneous
⊲ Isotropic
⊲ Infinite in size
⊲ No center
Infinite in time
(i.e. no beginning or end of time)
⊲ Always has been
⊲ Always will be
The Cosmological Principle: Newton’s version
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
⊲CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 29
To prevent one part of the Universe from collapsing
(i.e. into a black hole)
⊲ Homogeneous
⊲ Isotropic
⊲ Infinite in size
⊲ No center
Infinite in time
(i.e. no beginning or end of time)
⊲ Always has been
⊲ Always will be
⇒ Known as the Perfect cosmological principle.
⇒ Inconsistent with expansion!
Thought question
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
⊲ Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 30
What is the Universe expanding into?
(A) Nothingness
(B) Extra dimensions of space and time
(C) The Universe is not really expanding, it is stretching
Thought question
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
⊲ Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 30
What is the Universe expanding into?
(A) Nothingness
(B) Extra dimensions of space and time
(C) The Universe is not really expanding, it is stretching
What is expanding?
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
⊲What isexpanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 31
The spaces between faraway galaxies stretch
What is not expanding or stretching
What is expanding?
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
⊲What isexpanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 31
The spaces between faraway galaxies stretch
What is not expanding or stretching
⊲ You and I are not expanding
⊲ The Earth is not expanding
⊲ The Sun isn’t expanding
⊲ The entire Milky Way galaxy is not expanding
What is expanding?
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
⊲What isexpanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 31
The spaces between faraway galaxies stretch
What is not expanding or stretching
On small scales, the effect of the Universe’s stretching is
completely overwhelmed by other forces
What is expanding?
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
⊲What isexpanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 31
The spaces between faraway galaxies stretch
What is not expanding or stretching
On small scales, the effect of the Universe’s stretching is
completely overwhelmed by other forces
⊲ The atomic forces which hold people’s bodies
together
⊲ The Earth’s gravity
⊲ The Sun’s gravity
⊲ The Galaxy’s gravity
What is expanding?
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
⊲What isexpanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 31
The spaces between faraway galaxies stretch
What is not expanding or stretching
On small scales, the effect of the Universe’s stretching is
completely overwhelmed by other forces
On very large scales, the effect of the universe’s
stretching becomes noticeable above the effects of local
gravity and other forces which tend to hold things
together
What is expanding?
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
⊲What isexpanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 31
The spaces between faraway galaxies stretch
What is not expanding or stretching
On small scales, the effect of the Universe’s stretching is
completely overwhelmed by other forces
On very large scales, the effect of the universe’s
stretching becomes noticeable above the effects of local
gravity and other forces which tend to hold things
together
This is often called the Hubble Flow
Thought question
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
⊲ Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 32
You observe a galaxy moving away from you at 0.1 light-years
per year, and it is now 1.4 billion light-years away from you.
How long has it taken to get there?
(A) 1 million years
(B) 14 million years
(C) 10 billion years
(D) 14 billion years
Thought question
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
⊲ Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 32
You observe a galaxy moving away from you at 0.1 light-years
per year, and it is now 1.4 billion light-years away from you.
How long has it taken to get there?
(A) 1 million years
(B) 14 million years
(C) 10 billion years
(D) 14 billion years
Thought question
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
⊲ Thought question
Measurement in anexpanding universe
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 32
You observe a galaxy moving away from you at 0.1 light-years
per year, and it is now 1.4 billion light-years away from you.
How long has it taken to get there?
(A) 1 million years
(B) 14 million years
(C) 10 billion years
(D) 14 billion years
Hubble’s constant tells us age of universe be-
cause it relates velocities and distances of all
galaxies:
Age =Distance
Velocity≈
1
H0
Measurement in an expanding universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
⊲
Measurement inan expandinguniverse
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 33
How does the Universe’s expansion affect our distance
measurements?
Measurement in an expanding universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
⊲
Measurement inan expandinguniverse
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 33
How does the Universe’s expansion affect our distance
measurements?Distances between faraway
galaxies change while light
travels
Measurement in an expanding universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
⊲
Measurement inan expandinguniverse
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 33
How does the Universe’s expansion affect our distance
measurements?Distances between faraway
galaxies change while light
travels
Astronomers think in terms
of lookback time rather than
distance
Measurement in an expanding universe
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
⊲
Measurement inan expandinguniverse
Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 34
Expansion stretches photon wavelengths, causing a
cosmological redshift directly related to lookback time
Summary
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
⊲ Summary
Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 35
How did Hubble prove that galaxies lie far beyond the
Milky Way?
⊲ He measured the distance to the Andromeda galaxy
using Cepheid variable stars as standard candles
What is Hubble’s Law?
⊲ The faster a galaxy is moving away from us, the
greater its distance:
velocity = H0 × distance
How do we observe the life histories of galaxies?
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
⊲ Galaxian history
Looking back
Read: Chaps 20, 21 11/18/14 – slide 36
Observing galaxies at different distances shows how they age
Looking back
Announcements
Measuring distances
Tully-Fisher
3 types
Summary
Spiral Nebulae
Hubble’sMeasurement
Modern relation
Age of the Universe
Expansion of theUniverse
CosmologicalPrinciple
Thought question
What is expanding?
Thought question
Measurement in anexpanding universe
Summary
Galaxian history
⊲ Looking back
Read: Chaps 20, 21 11/18/14 – slide 37
Deep observations
show us very
distant galaxies as
they were much
earlier in time
(Old light from
young galaxies)
Recommended