The Bridge V Learning Edition 1 ; our solar system | Page 58

ˆ II) Spirals and Barred Spirals: it can be hard to tell these apart. If you know it's either an S
or SB, it is okay to guess between these two.
ˆ III) Irregular galaxy.
ˆ IV) Uncertain: an edge-on view of a galaxy that could possibly be an S0, SB0, S, SB, or IR.
There are too many possibilities, so do not count these.
ˆ Star) any object that has ‘crosshairs’ sticking out of it is a foreground star in the Milky
Way galaxy, so do not count these.
ˆ ?) Don't count small, faint objects like these that are too hard to classify.
Step 5
Download the images “Galaxies Cards” A-D to count the types of galaxies seen in each image.
Count the number of galaxies of each morphological type and write down the number in the
correct spot in the table.
Step 6
Tell students: Galaxies are found throughout the universe, from our next door neighbours —
the Magellanic Clouds and Andromeda — all the way out to the visible universe 13 billion light
years away. Galaxies live in a variety of environments. Sometimes large numbers of them are
packed close together in clusters, such as the Coma Cluster; sometimes they gather in smaller
numbers called groups, like the Local Group that contains the Milky Way; and sometimes they
are isolated far from one another in the field. The table below shows the different properties
for the different types of galaxy environments. In the previous step, Galaxy Cards images A and
C show the dense central core of the Coma Cluster, and images B and D show galaxies out in the
field. (NB Astronomers sometimes use the term "field" to mean the area outside galaxy
clusters.) Fill in the tables using the numbers you wrote down in the table from step 5 of the
activity.
See tables in the worksheet.
Step 7
Ask students to think about and discuss in groups: What trends do you notice from the data
you've analysed above? Do you notice anything about where different types of galaxies tend to
be found? (Extra prompt: Do you tend to see more spirals in the dense cluster or in the field?
What about ellipticals?) Students should notice that spiral galaxies are more common in the
field, and ellipticals are more common in dense clusters. Follow-up question: Does that seem
surprising? The goal here is to get students to ask "Why does the number of spiral galaxies (or
elliptical galaxies) depend on where the galaxy is located?" Ask students to discuss and write
down ideas for why galaxy type seems to be affected by where the galaxy is located.Ask
students how they could investigate their ideas: What predictions would their ideas make? What
additional observations or information would they want to have?How could they quantify this
trend using the data?
Step 8
The following steps tell how students can investigate this trend, first by quantifying it, and then
by reading more information about how galaxies form and evolve. You can tell them exactly
what to do as below.---Better yet, have them discuss in groups how they could investigate their
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