Girls Exploring the Universe!

July 8 - 12 2019, University of Virginia

 The Expanding Universe on a Balloon


We live in a Universe that is expanding, which means it's getting bigger and bigger everyday. But what does an expanding Universe really mean? Is it getting bigger? Where is the Universe expand into? Does the Universe have a center?

To understand these questions, all we need is a balloon, a ruler, and a few markers. Each group needs:

1.     A balloon blower

2.     A distance measurer

3.     A timekeeper and scribe


Steps to blowing up the Universe:

1.     Blow up your balloons just a little bit. Draw 10 – 20 galaxies on the surface of your balloon.

2.     Mark one galaxy “Home” or “The Milky Way”,  and number 5 other random galaxies from 1 – 5.

3.     While the balloon blower holds the balloon, the distance measurer uses the ruler to measure the distance from your home galaxy to the other five galaxies.

4.     Enter these distances in the first column of the following table, under “First Distance D1 in cm”.

5.     Now carefully blow the balloon a bit more.  The timekeeper is in charge of keeping track of the balloon blowing time. Write down the time in seconds under the table.

6.     Measure the distances from your home galaxies to the other galaxies again and write them down in the second column of your table “Second Distance D2 in cm”.

7.     You now need to work out the speed of each galaxy. Remember that:

Speed = Distance traveled / Time taken

Here, Distance traveled is the difference between D1 and D2, so calculate D2 - D1 for each of your galaxies and write them in the 4th column on the table, “Change in Distance D1 – D2 in cm”

8.     The Time taken is the time to blow the balloon up. Calculate the speed V for each galaxy and write it in the 5th column, “Speed V in cm/second”. Because your "home" galaxy has not moved, its speed will be zero.

9.     You should find that the speeds that galaxies seem to have are larger for galaxies that are further away.

The best way to understand this is to plot a graph showing the distance along the x axis and with the speed on the y axis.

This means that you need to plot your data on the graph in your packet.

Use D2 as the Distance and V as speed on this plot. Here is an example of the axes.

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