Note: This activity is based on the Transit Tracks activity that appears on the NASA website: Transit Tracks. The copyright for the original Transit Tracks is held by the Regents of the University of California.

In this quick opening, you’ll be introduced to the concept of transit. Rather than just telling you what transit is about, your teacher will demonstrate it using a lamp and beads. Showing you what transit looks like should help you understand the concept. Transit is important for understanding how we find planets, which you will learn more about later in this lesson. 

Watch your teacher demonstrate transit. Remember that the lightbulb represents a star and the bead a planet. The planet is orbiting its star, like the Earth or Venus orbit the Sun.  

As your teacher swings the bead around, can you see it go directly in front of the star? If not, your teacher may ask you to move so that you can see it go in front of the star. Once you can see it, note that what you are observing is what people call a transit. Transit is an event where one body crosses in front of another, like when a planet goes in front of a star. What do you notice when you see transit?

Now, your teacher will try the same thing but with different sized beads, on different lengths of string. How do you think the transit will change with shorter or longer strings and different sized planets? Will the orbit change? A planet’s orbit distance is called a period, which is defined as the time it takes for a planet to make one orbit around its star.

Think about the differences between each of the “planets” that your teacher has swung around. What do you notice about them? What do you notice about them in relation to the light? 

In this video, Phil Plait explains that the sky is filled with planets outside of our Solar System, and that nearly 2,000 have been found so far. The most successful method for finding stars is using transits. Another way is to measure the Doppler shift in a star’s light, which is caused by reflexive motion. We think there may be many billions of Earth-like planets in our Universe. 

In this video, you learn that there are other planets in the Universe as well as different ways in which scientists find other planets. This video explains how transit and the Doppler effect help us find stars. This will help you think about what would happen if you were to flee the surface of the Earth, and how you would make decisions about where to go. It also helps you understand how you would go about detecting planets. If the Earth’s existence were in jeopardy, it might be important to know if there are other habitable places in the Universe. 

Preview

In this Crash Course video, astronomer Phil Plait talks about the existence of other planets in the Universe. He discusses some of the methods that scientists use to detect these planets, and explains why there may very well be billions of Earth-like planets out in the Solar System. 

Key Ideas – Factual

Think about the following questions as you watch the video:

1. Why can’t we see planets that are orbiting other stars in the Universe?
2. What is reflexive motion?
3. What are exoplanets?
4. How did Swiss astronomers Michel Mayor and Didier Queloz find a planet orbiting a sun-like star?
5. How do we make sure that we know something is an exoplanet and not a star spot, a pulsating start, or a background star messing up the measurements related to the Doppler effect?
6. Exoplanets orbit what kinds of stars?
7. What are some of the things we need to know about Earth-like planets to determine whether or not they are habitable? 

Thinking Conceptually

Do you think it’s worth looking around the Universe for other planets? Why are astronomers so intent upon finding other planets, and how might that be important to us today?

Astronomers use a variety of techniques to find exoplanets. One of the simplest and the most common is transit. This is when we can see a planet move directly in front of a star, temporarily dimming the light from that star. While a relatively simple approach, it requires the star and planet to be aligned with Earth and can result in false positives when the Sun dims for other reasons, such as dust passing between the Earth and that star. 

This article details the various tools astronomers use for finding planets across the galaxy. It shows the range of techniques and the creativity astronomers sometimes have to employ to draw conclusions when very little information is available. 

Skimming for Gist

In this lesson, we will take a careful look at the process of observing transit. Although a relatively simply process, it requires conditions to be just right and can lead to some false positives. However, astronomers rely on a number of other techniques in addition to observe planets. 

Understanding Content

By the end of the second close read, you should be able to answer the following questions:

1. What is transit?
2. What are the disadvantages to transit as a method of detecting exoplanets?
3. What is orbital brightness?
4. What is radial velocity?
5. What is direct imaging? 

Thinking Conceptually

Will any of these techniques help us observe bodies here in our own Solar System? 

Note: This activity is based on the Transit Tracks activity that appears on the NASA website: Transit Tracks. The copyright for the original Transit Tracks is held by the Regents of the University of California.

In this activity, you’re going to interpret graphs that show the transit of planets across stars, moving your understanding of transit beyond the conceptual into something applicable. This should help you understand how scientists find planets outside of our Solar System, and what they can find out about the planets from transit information alone. 

Imagine that you have a light sensor that will help you measure the brightness of a star (the bulb). What happens to the reading on your light sensor when your teacher passes an object in front of the “star” (bulb)? If you were to plot a graph of brightness versus time, with brightness measured by your light sensor, and an object transited the light for 3 seconds, what would the graph look like? What about if an orbiting planet passed in front of the star—what would that look like? How would the graph change for a bigger or smaller planet?

Transit graphs and transit data help in calculating a planet’s diameter and distance from its star. Why do you think those two properties (planet diameter and distance from its star) would be important to know? Be prepared to discuss your ideas with the class.

Now that you have a general understanding of how transit works, you are going to interpret some transit graphs in groups. Remember, the larger the planet, the bigger the dip you will see on the graph. 

In this lead-up to the final activity in the Fleeing the Surface of Earth challenge, you will use the knowledge you’ve gained in the last two lessons to decide whom you might bring with you as you flee. This should help you think about what different types of scientists know and are able to do, and how your knowledge of astronomy and the Solar System may or may not help you on your journey and at your final destination. 

Join your Fleeing the Surface of the Earth group, and think about who you would want to take with you on your journey. What questions would they ask about where you’re going? What do they already know about where you’re going? Also, think about why you did or did not choose an astronomer to go with you based on what you’ve learned in the last two lessons, and how that is or is not applicable to this challenge.

Once you’ve completed the worksheet, be prepared to share your choices for your team with the class, and explain why you chose them. 

In this activity, you will finalize your plans for fleeing the surface of the Earth. This should help you apply some of the knowledge you’ve learned in the last two lessons. In addition, you will incorporate your understanding of Goldilocks Conditions and how those help you better understand the conditions of your final destinations, and how that helps you determine where you go and how you should prepare for your journey. 

In this activity, you’re going to finalize your plans for Fleeing the Surface of the Earth, and then present them to the class. Based on your new knowledge of planet hunting, might you choose to go somewhere else? Or, will your new understandings of transit and distance from stars help you decide when to depart for your chosen location?

In addition to finalizing these plans, you are now going to think about the Goldilocks Conditions that do or do not exist in your final destination. What conditions exist that will help you survive there? What conditions are needed that don’t exist, and how might you create those conditions?

As part of your final presentation, you will provide the following information:

• Final destination and reason for going there.
• Team of people you will bring with you to this destination and why (refer back to the What Do You Know? What Do You Ask? activity that you just completed).
• How far away is your destination?
• How you will get there and how long it will take?
• Which Goldilocks Conditions do or don’t exist there for you to survive, and what would you have to do to make up for the ones that don’t exist?
• Proof of claim testing for at least three of the bullet points listed above.

Now, here’s an added twist—you can’t just present this information to the class. Rather, you have to predict your journey based on your final decisions, and present a narrative about what happened on the journey. This narrative should include all of the information in the list above. You can use different kinds of media to present the narrative, including a video, an RSA animate, or anything else you might come up with. Make sure you get approval from your teacher for the medium you decided to use. Also, make sure to review the BHP Presentation Rubric as you’re preparing your final product so you know exactly what you are being graded on!