Astronomy and Space Sciences

Strategies

This unit is based on a constructivist, student-centered, hands-on approach in which students are encouraged to create models of the Universe that make sense to them. The students are asked to make qualitative and quantitative observations whenever possible, perform labs and calculate quantities and apply the knowledge that they acquire to facts that science has determined about the Universe. The goal is to develop enough scientific knowledge that the students are able to explain the main topics about what science currently knows about the Universe and how they know it, and to be able to make a discerning evaluation of scientific claims.

The knowledge of cosmology, and science in general, is evolving and the intent of this unit is to engage students in a scientific process to be able to appreciate how science knows what it claims to know. Partly, this will be achieved by guided questioning. It is my belief that instilling an enthusiasm for science through exciting hands on activities and relevant and challenging intellectual stimulation will produce more informed citizens who appreciate the utility of the scientific method.

Classroom Activities

5 Lesson Plans- How Do We Know What We Know?

Lesson 1: What is the Evidence for the Big Bang?

Objective: Students will be able to explain the evidence for the Big Bang Theory and discuss why it is our best current explanation.

Activities:

LAB: The Big Bang: An Analogy to an Expanding Balloon

Part 1: Observations

Give each group of 2 or three students a balloon. Have them mark dots on the deflated balloon to indicate the position of galaxies. This deflated balloon represents the early Universe (assuming that galaxies had already formed). Now have the students blow the balloon up slowly. Ask the students to discuss what happens to the galaxies (dots) as the balloon is inflated.

Determining the Expansion Rate of the Universe: Qualitative Analysis

Have the students blow up the balloon slightly. Tell the students to mark one "galaxy" ñ"US." Then put a number "1" on a "galaxy" close to "Us." Mark a "2" on a galaxy about a quarter of the way around. Lastly, mark a "3" on a galaxy as far away as possible (about half way around the balloon). Have the students deflate the balloon and tell them that the balloon represents the Universe (but if it were really accurate the balloon would shrink to a point). Have the students inflate the balloon a little. Now ask the students again what is happening to the distance between "US" and other "galaxies." What happens to the distance between "galaxies" that are close? What happens to the change in distance between galaxies that are far apart? Continue these steps a couple of times. Discuss with the students what is happening to the distance between galaxies.

Explain to the students that this is an analogy of our model of the Big Bang, and that their observation that the distance changes more the further you are away is true in the Universe. The further away galaxies are from us, the faster they are moving away from us! Collect the balloons and tell the students to remember this analogy and we will come back to it later.

Thought Experiment: Cosmic Microwave Background

In the 1960's, researchers detected microwaves coming to us from every direction with the same temperature, 2.7 degrees Kelvin. This is now known as the cosmic microwave background (the CMB). Where could this "light" have come from" Why is it all at the same temperature? Why is it microwaves? How is this proof of the Big Bang?

Thought Exercise: Redshift

Since we cannot measure the distance to galaxies directly, we must use another method. It turns out that in astronomy we use the same technique you use every day to cross the street. When you cross the street do you have to look to see if cars are coming? Is there another way to tell? Yes, you can listen. And what does it tell you? How can you tell if a car is coming? Can you tell if it is going faster or slower? Does it make a different sound as it goes past you? This is the Doppler Effect! An object coming toward you makes a higher pitch and an object going away from you makes a lower pitch. A faster object that makes a sound is received at a higher pitch and the slower object that makes a sound is received at a lower pitch. The Doppler Shift for sound is the same as the redshift for light! Measuring the change in the frequency of light is how we tell how fast stars are moving and in what direction.

Doppler Demonstration:

Demonstrate the Doppler Effect with the Doppler Demonstrator, which is just a noise maker at a constant pitch attached to a string. Swinging the Doppler Demonstrator over your head causes the listener to hear a higher pitch when the "noise maker" is coming towards them and a lower pitch when it is moving away.

Explanation of the redshift:

The redshift is graphed to determine the rate that galaxies and supernovae are moving away from us relative to their distance from us. The cosmic redshift is the same thing we saw with the balloon. The farther away you are the faster the objects are moving away. So like the balloon, we can run it in reverse to prove that the whole Universe would collapse down to one point! This is the Big Bang in reverse!

Discuss "The History and Fate of the Universe" CPEP Chart

Lead a discussion on what information is presented to us by the timeline of the early Universe to the present.

Lesson 2: How Old is the Universe?

Activities:

LAB: The Big Bang: An Analogy to an Expanding Balloon - Part II (See Lesson 1 for Part I)

So, we know from the theory of the Big Bang that the Universe is expanding. Today we are going to discuss the rate of expansion and how we can calculate what that exact rate is.

The students should then copy the following chart:

Determining the Expansion Rate

Distances to Distant Galaxies

Hand out the marked balloons from Lesson 1, and give each group a length of string and a meter stick. Now, we are ready to begin.

Step 1: Using the string, have the students measure the distance between "US" and galaxy "1". Then measure the distance between "US" and galaxy "2". Measure the distance between "US" and galaxy "3".

Step 2: Using the string to measure, mark a distance twice the distance between "US" and galaxy "1". Now, blow up the balloon so that the distance between "US" and "1" are this far apart (twice the distance that "US" and galaxy "1" was in Step 1. Have the students mark this distance on their chart. Then, have the students measure the distance between "US" and galaxy "2", and measure the distance between "US" and galaxy "3".

Step3 and Step 4: Repeat step 2, measuring what the distance is between "US" and the three other "galaxies".

Graph Results:

Have the students plot the distance between galaxies vs. the step (which are proportional).

Find the slope of your line- this is your "Rate of Expansion"!

Conclusions:

What did you find? How do the distances vary as you get further away? Did you get a straight line? What is the slope of your line? What does a positive slope of a straight line indicate about your "Universe"? Your result is equivalent to the Hubble Constant, which gives us the rate of expansion of the Universe!

Activity: Calculating the Age of the Universe

As it turns out, the Hubble Constant is 22 kilometers per million light years away an object is from us. This is the result of the cosmological redshift.

Age of the Universe is simply the reciprocal of the Hubble constant, H ₀.

v = H ₀d; d = vt; so by substitution v = H ₀vt. The v's cancel so 1= H ₀t, So solving for t: the age of the Universe t = 1/ H ₀!

The Hubble constant H ₀ is 22 km/s/million light years:

First we must convert light years. A light year is a distance, but we will convert light year into km/s for 1 year for the ease of cancellation with the Hubble constant. (distance/time x time = distance)

1 light year = (3 x 10 ⁵ km/s for 1 year)

So:

If we do the math, 1/22/((10 ⁶)(3x10 ⁵km )= 3 x 10 ^{1 1}/22 = 1.36 x 10 ^{1 0} years!

So the age of the Universe is 13.6 billion years!!!

Lesson 3: Are We at the Center of the Universe?

Activities:

LAB: Are we at the Center?

Repeat the Big Bang Lab (Part 2) in Lesson 2, but this time use "1" as your center and measure from "1" to the other galaxies. Does this change your results? Does it change your graph? If so, how? So, can you say which point "us" or "1" is at the center of the galaxy? What if we repeat the lab for galaxy "2". Do we get the same result?

Explain that every galaxy is moving away from every other galaxy, and they all "collapse" back to the center where the deflated balloon was, so no one point is the center! The center is the singularity, the point from which the Big Bang started.

Video Resources:

Show the students segments of the following videos to enhance their comprehension of our place in the Universe. View clips from Runaway Universe that indicate that the Universe is expanding and that the Hubble constant is the same anywhere in the Universe. Show the students clips of Steven Hawking's Universe to illustrate characteristics of the Universe. The Astronomers series indicates the approach scientist take to making astronomical discoveries. The segment on Robert Kirshner's search for supernovae is particularly engaging. And lastly, the eclectic and engaging Elegant Universe addresses the bizarre implications of quantum mechanics, which is essential to understanding the early universe. These video clips will stimulate the students' imagination and impress upon them the magnitude and wonder of the cosmos.

Lesson 4: What is the Evidence for Dark Matter?

a) Kepler's 3 ^rd Law with masses P ²=(4Π ²/(G(m ₁+m ₁))a ³

We would expect the velocity to decrease by when you go beyond the galaxy because we are further from the mass, but it doesn't! Instead it remains constant. Therefore, there must be mass beyond the galaxy that we can't see!

b) the velocity of galaxies within clusters

the velocity of galaxies within clusters are greater than the escape velocity for the visible mass, but the galaxies continue to orbit, so there must be dark matter that we don't see.

Lesson 5: What is the Evidence for Dark Energy?

The recent supernova data for high z (redshifted) objects has shown a departure from the slope of H ₀, that indicates an increase in the rate of expansion of galaxies starting about 5 billion years ago. So, the expansion of the Universe is accelerating!

Give the students a copy of a graph of current supernovae data showing that the expansion of the Universe is accelerating.

(NASA and A. Field)