The Bridge V Learning Edition 1 ; our solar system | Page 55

These discussion points can be re-visited later in the activity as well. (Presumably at least some
students will come up with classification schemes based on shape---but if they do not, after
discussing their schemes, encourage them to come up with other schemes that are based on
shape.)
Prompt students to make observations and ask questions based on their analysis of the image
so far, discuss them in groups, and write them down. The goal is for them to ask, "Why do
different galaxies have different shapes?" Then, prompt students to discuss and write down
questions and ideas about why galaxies might have different shapes---for example
ˆ Did the galaxies form in different shapes, or did they all form in the same shapes and
then evolve into different shapes?
ˆ What different histories could different galaxies have (especially, that could affect their
shapes)? (encourage students towards the idea of galaxies interacting with each other)
ˆ Could the evolution of galaxy shape be due to internal processes or driven by external
processes? (e.g., something that happens to all galaxies over time no matter what, or
something driven by an interaction with another galaxy)
ˆ Could the shapes be related to the size of the galaxy when it forms?
ˆ Are the shapes we observe transient or long-lasting?
While students are thinking of these kinds of ideas, encourage students to discuss how they
could investigate the answers to these questions. (Perhaps some students will think of the idea
that interactions with other galaxies could be important, and that looking at regions where
there are many galaxies so many interactions take place might be a way of investigating this.
Whether they come up with this idea or not, this previous discussion will help them to be in a
better position to think through this idea later in the activity.)
Step 3
Tell students: Astronomers have developed their own classification scheme for galaxies, based
on the galaxy shape (often called "morphology").The definitions of the main galaxy types which
astronomers use are listed below. Using these definitions, place the 12 galaxies shown in the
above figure into their commonly-used categories. Fill in the table in the worksheet.
www.space-awareness.org