We started BHP 2.0 The Big Bang this week. Students watch videos and read articles from BHP at home. Those who want to dig deeper into the astronomy can also read Chapter 17 Cosmology in Foundations of Astronomy. I started class with a slideshow about cosmology, redshift/blueshifts and the expansion of the universe. I had originally planned on just doing the Big Bang Balloon from BHP 2.3 but while putting the slideshow together I found this great lab, The Incredible Expanding Rubber Band. You can download a pdf version from links at the top of her page. Students take a rubber band (cut so its no longer a loop) with 7 marks on it and measure the distance of those marks from the first one – with the rubber band relaxed. Then they stretch the rubber band so that the distance between the first two marks doubles – if it was originally 1 cm, they stretch it until its 2 cm. Then they record the position of all the stretched marks. 
Students find the change in the distances and then the speed (change in distance divided by 2 seconds, the time we’re assuming it took to stretch the rubber band). They will see that the marks farther away from the starting point have moved farther and the speed is also greater…. just like galaxies that are farther away from us have a bigger redshift and are moving away from us at a faster rate. Plotting the speed as a function of the original distance gives the students a linear graph (or at least it should) and the slope is equivalent to the Hubble constant for the rubber band universe. If you take one over the slope you have a time, the ‘age’ of the rubber band universe or the time it took for to expand from a size of zero to the relaxed length at the beginning of the lab.
This was a nice lab, data is easy to take and the math involved is pretty simple but the graph provided in the hand out is blank so students had to figure out which parameters to graph and what scale to use on the graph paper. They also got some practice with finding the slope. The handout and website by Michele Stark go through an example set of data making it pretty easy for students to follow along with their own data.
Since this lab didn’t actually take very long, I also had the high school class do the balloon universe lab provided by the Big History Project. Each group blew up a balloon to about 10 cm in diameter and used a sharpie to put 5 dots on it, 1 for the Milky Way galaxy and 4 other galaxies labeled A, B, C, D. They then measured the distances (with string) from the Milky Way dot to each of the other dots and recorded them in the table. Then they blew the balloon up a bit bigger and repeated the meaurements and repeated this procedure 2more times so they had a total of 4 sets of measurements. They should see all the points getting farther away each time the balloon universe expands and the points that started out farthest away from the Milky Way dot moved the farthest with each expansion.
Lastly, I handed out a color printout of the last page of the Narrative and Thresholds activity (BHP 2.0) and the students filled in the Big Bang space with some hashtags that they felt described the first threshold. I told them to make sure they saved this sheet since we’l be coming back to it as we learn about each threshold. I did this activity with both the high school and middle school classes.
For the middle school class, I did the same slideshow and demonstrated the expanding rubber band universe but only had them do the expanding balloon lab from BHP. We also took a look at parallax since we didn’t get to it last week. Instead of having the students measure the angles, I just had them sketch 4 stars that I placed around the room while standing on one side of the room and then move to the other side and sketch them again. The two stars that were on the back wall (blue and yellow) didn’t really change much, but the two stars that were closer (orange and green) to them moved quite a bit in relation to the back ground stars. If you were to list the stars from left to right, you’l notice the order of the stars is different in the two photos, yellow, green, orange, blue when viewed from the left side of the room and orange, green, yellow, blue when viewed from right side. Not to mention the green and orange stars appear much closer together in one image than the other. I explained to the students that by measuring the apparent motion of the stars we can calculate their distance. Closer stars, like the orange and green ones in the activity, appear to move more than stars that are farther away.
I finished the middle school class with Our Place in Our Galaxy: Size and Distance Scale, an activity you can find on the Night Sky Network website. This scale model asks the students to imagine our solar system shrunk down to the size of a quarter and then asks, what size is the Milky Way Galaxy on this scale? Well, the distance from the Sun to Pluto is about 5 1/2 light hours (takes light 5.5 hours to travel from the Sun to Pluto) and the Milky Way is approximately 1000 light years across so its going to be a LOT bigger than our quarter…. 2500 miles, about the distance from one side of North America to the 
other! The activity then asks the students how many stars are in the Milky Way (200 billion), and how can we represent them in our model? I pulled out some millett bird seed and explained that even one of those little seeds was much bigger than most of the stars in this scale model but that’s what we’re going to use. So what does 200 billion little seeds look like? Would it fill a shoe box?..a room? How about a football field, 4 feet deep!!! Eveyone’s eyes get pretty big at this… that is a lot of bird seed and they finally start to understand the large numbers involved. To complete our scale model of the Milky Way we have to distribute the stars (seeds) across the Milky Way (North America). To show how far apart the stars will be, I explained that our nearest star, Alpha Centauri is about 4 light years away, so for our model we’d have to put one bird seed 2 football fields (600ft) away from our Solar System quarter. The link to the activity has resources to print out and a script you can use with your students.
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