Brief Overview:
Students will observe examples of galaxies that have different shapes.
Students will observe how the galaxy classification system of Edwin Hubble assigns galaxies to different groups according to their shapes.
Students will attempt to categorize unknown galaxies according to the Hubble classification descriptors.
Directions:
Go to the website http://cse.ssl.berkeley.edu/SegwayEd/lessons/classifying_galaxies/student1.htm
Read the introductory paragraph; then click Start your galaxy exploration here! Use the information in your reading to fill in the blanks below.
Read the page, “What is a Galaxy?”; you should click on and read the information at the following link buttons:
· Edwin Hubble
· Elliptical galaxies
· Spiral galaxies
· Barred spiral galaxies
· “Click here to review”
· The Tuning Fork Diagram
What is a galaxy?
In the 1920's, an astronomer named Edwin Hubble was able to gather pictures of many galaxies. He noticed that they were not all alike. He decided to group, or classify them. To group the galaxies in the photographs he studied, he could have used size, color, shape or any other feature that he noticed . Hubble decided to classify galaxies by their shape or form.
Edwin Hubble looked at many galaxy pictures and decided to divide galaxies into three types according to the way they looked. He used letters to represent these three types of galaxies.
The letter "E" meant_________________galaxies, "S" meant _______________galaxies, and "SB" meant ___________________galaxies.
Galaxies had so many shapes that Hubble found that three types were not enough.
He had to further break down these three according to a slight variation in
shape between each type of galaxy in each category.
For the "E" or _________________galaxies, he used the amount of
flattening or _____________, from E0( E zero) to E5, to put the galaxies into
smaller groups.
For the "S" or ____________ galaxies, he used how tightly the arms
were wound around the bright _______________, to further classify these galaxies
as Sa, Sb, or Sc.
For the "SB" or ___________________________ galaxies, he used the
increased openness of the ____________to group these galaxies as SBa, SBb, or
SBc.
Edwin Hubble took all these ideas and presented them all together in a simple diagram for classifying galaxies. This diagram is called the Hubble Tuning Fork Diagram. Most galaxies fall into one of his groups, according to how they look. Draw a shape for each of the types of galaxies below. Draw it above the letters which he used to identify the shapes.
Sa Sb Sc
E0 E5 S0
SBa SBb SBc
Classifying Galaxies (Part II)
Go to my website (www.portervillecollege.edu/satko) and follow the links:
Astronomy 101 à Astronomy assignments à Classifying Galaxies, Part II.
On the Classifying Galaxies page, you will be provided a set of photographs of galaxies. Classify each one, according to Hubble’s system. Some of them may be vague, but do your best!
The choices are: E, S0, Sa, Sb, Sc, SBa, SBb, SBc and Irr. If you can guess at a numeral designation for an elliptical galaxy (e.g., E7), then do so. Also keep in mind that some may be Irregular galaxies (not covered in Part I of this lab).