Hubble’s Law Lab Activity
ONLINE PHYSICAL SCIENCE II Name: .
Lab Activity
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:
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.
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.
To make sure you understand the key concepts essential to this lab, answer the following questions based on your textbook reading assignment:
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http://depts.washington.edu/astroed/HubbleLaw/galaxies.html
Data Table:
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