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Hubbles Law 1

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Physics

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Collin County Community College District

Course

Physics

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ONLINE PHYSICAL SCIENCE II Name: .

Lab Activity

”Hubble’s Law”

Overview:

In the 1920's Edwin Hubble investigated the relation

between distance to galaxies and their velocity toward or

away from us. He found that most galaxies are moving away

from us. In a paper published in 1929, Hubble reported a

linear relation between distance and velocity, now known as

the Hubble law. One of the implications of Hubble’s law is

that our universe is expanding and thus had a beginning.

To prepare for this lab activity you should carefully read

through pages 413-419 of your textbook which covers

Hubble’s law. In this lab activity you will make use of a

simulation to explore various aspects of Hubble’s law.

Objectives:

1. To understand the concept of Hubble’s law

2. To measure the redshift of several galaxies which Hubble observed by using galactic spectra

3. To measure the angular size of these galaxies

4. To determine if any relationship exists between the galactic redshift and angular size

5. To explore what that relationship means and what it implies about our universe

Theory:

Hubble used the redshift of galaxies

he observed to determine their

velocity. All galaxies emit a wide

spectrum of light of various

wavelengths. But these spectra have

something in common: the calcium H

and K absorption lines. These are

particular wavelengths of light that

have rest values of 3933 angstroms

(for K) and 3968 angstroms (for H)

and are produced by all galaxies.

To the right is an absorption spectrum

of galaxy NGC 2775. Note the

predominate Calcium K and H lines.

These same lines and their relative

position always appear in galactic

spectra. However they will be shifted

either right or left depending on

whether the galaxy is moving away

from or toward the earth.

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The amount of redshift due to the velocity of an observed galaxy can be calculated using the following equation:

Redshift = [Observed wavelength – Rest wavelength] / Rest wavelength

To determine the redshift, you need to calculate from the spectra the ratio of the observed wavelengths of the H and

K lines to their rest wavelengths. For example, suppose the observed wavelength of the H line is 3988 angstroms

for a distant galaxy moving away from us. In this case the redshift would be:

redshift = (3988 - 3968)/3968 = 0.005

The faster a galaxy is moving away from us the larger its redshift. This lab makes use of a java applet in which you

will measure the observed wavelength of the H line for several galaxies. In fact you will be using the same galactic

data that Hubble used! You will also measure the angular size of the galaxies which correlates to their distance

away from earth. Your goal is to see if there is a relationship between the redshift of these galaxies and their

angular size, just as Hubble did.

Review Questions:

To make sure you understand the key concepts essential to this lab, answer the following questions based on your

textbook reading assignment:

1. What debate did Hubble put to rest with his discovery?

Upon his discovery Hubble put to rest the debate of whether earth is still expanding. .

2. What is redshift (p124)?

Redshift is a theory that is used determining the distances in the universe. .

3. How did Hubble use redshift to measure the speed of galaxies he observed?

Through the light frequencies coming for the galaxies that seemed to shift to the lower frequencies .

4. Write the mathematical expression for Hubble’s law:

V=H

D .

5. What does the constant H

in Hubble’s law represent?

is the proportionality constant between the D distance and the velocity V. .

6. What are two problems astronomers encounter when trying to use Hubble’s law to measure galactic distances?

Because distance – the techniques used in measuring rely on the bright objects and heri luminosities may be

infeered

Anotehr problem is that the objects may become difficult to trace due t intergalactic space. .

7. List the six techniques astronomers typically use to measure cosmic distance. In what way are they part of a

chain?

SBF technique

Radar

Cepheids

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ONLINE PHYSICAL SCIENCE II Name: Lab Activity ”Hubble’s Law” Overview: In the 1920's Edwin Hubble investigated the relation between distance to galaxies and their velocity toward or away from us. He found that most galaxies are moving away from us. In a paper published in 1929, Hubble reported a linear relation between distance and velocity, now known as the Hubble law. One of the implications of Hubble’s law is that our universe is expanding and thus had a beginning. To prepare for this lab activity you should carefully read through pages 413-419 of your textbook which covers Hubble’s law. In this lab activity you will make use of a simulation to explore various aspects of Hubble’s law. Objectives: 1. To understand the concept of Hubble’s law 2. To measure the redshift of several galaxies which Hubble observed by using galactic spectra 3. To measure the angular size of these galaxies 4. To determine if any relationship exists between the galactic redshift and angular size 5. To explore what that relationship means and what it implies about our universe Theory: Hubble used the redshift of galaxies he observed to determine their velocity. All galaxies emit a wide spectrum of light of various wavelengths. But these spectra have something in common: the calcium H and K absorption lines. These are particular wavelengths of light that have rest values of 3933 angstroms (for K) and 3968 angstroms (for H) and are produced by all galaxies. To the right is an abso ...
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