Waves Traveling the Universe

Display the first slide, on the tab labeled "a word." Ask:

Has anyone ever heard of the word "extraterrestrial"?

Some of your students may have heard the word as a synonym for "alien," as in the movie E.T. the Extra-Terrestrial (1982).

Display the second slide on the tab labeled "break it down." Paraphrase:

Let's break down the word into its parts. The prefix "extra" means "out of" or "beyond" while "terr" is for "Terra," another name for our planet Earth.

The electromagnetic waves traveling across the universe are mainly extraterrestrial.

Display the third slide on the tab labeled "the Universe." Ask:

Are there extraterrestrial civilizations out there in the Universe?

Give the students a few minutes complete a KWL chart individually or to turn and talk in a pair-share. Ask students to share their viewpoints with the class. Student interest here is very high, so as they discuss, interject lightly to provide new information or answer questions based on the slides.

For example, you can display the third slide (on the tab labeled "the Universe") and say something along the lines of:

We live in a galaxy, the Milky Way, that is just one among 100–200 billion galaxies in our universe.

Looking through telescopes like the Hubble that captured this image is like a kind of time travel, in that we're looking at light and radio signals from hundreds of thousands of years ago.

If students wonder how many inhabitable planets there are, display the fourth slide (on the tab labeled "the Milky Way"). Paraphrase:

Our own galaxy, the Milky Way, has about 300 billion stars. Each of those stars could have a planet orbiting within a zone that could sustain life.

If students wonder how likely it is that Earth is the only planet with life, display the fifth slide (on the tab labeled "the odds"). Note: this figure is derived from the Drake equation which multiplies seven different factors together to result in this value. Paraphrase:

Through their calculations, scientists figure that the chances of Earthlings being the only beings ever to develop a civilization at about 1 / 1022 — that is, one in 10 billion trillion.

Put another way, scientists believe there's a 99.9999999999999999999% chance there's another civilization out there.

If students wonder whether we have ever heard from another civilization, display the sixth slide (on the tab labeled "Wow! message"). Paraphrase:

The search for extraterrestrial intelligence is called SETI, pronounced "SET-ee" rhyming with Betty.

Have you ever seen a radio with a tuning knob? It makes a lot of noise between the stations. When we listen to the stars we hear the noise cooked up by the cosmos. There's a lot of background radiation criss-crossing the universe.

For 72 seconds in 1977, Ohio State University's Big Ear radio telescope received what SETI researchers considered the most likely possibility of an alien radio transmission ever seen or heard. The data were so impressive, an astronomer monitoring it wrote "Wow!" next to the printout.

Look at all the numbers around it. It really stood out compared to the usual data coming in. The Wow! Message is like a shape or clear sound suddenly emerging from a chaotic background.

But what could "6EQUJ5" mean, if anything?

In 2017, astronomers finally realized the signal was made by a comet, not an extraterrestrial civilization after all.

In this section, students read an article that considers the pros and cons of SETI.

Paraphrase:

You may have seen movies where people from Earth explore other planetary systems, and where explorers from other planets come to Earth.

The Search for Extraterrestrial Intelligence (SETI) is our primary way of looking for off-Earth civilizations.

We'll read an article that considers a few of the pros and cons of making contact with other societies.

Distribute the article for students to read. The article was adapted from "We just beamed a signal at space aliens. Was that a bad idea?” by SETI’s Senior Astronomer Seth Shostak for NBCNews MACH (November 2017).

Consider using the Reading to Learn Science (RTLS) strategy Listening Triads to have the students read this opinion piece. If you want to use this strategy, the teacher tips and students guidelines are shown in the next section of the Teacher Notes for this lesson plan.

Image credit: NASA/JPL-Caltech Radio telescope in the Mojave Desert, similar to the one used in Tromsø, Norway.

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We just beamed a signal at space aliens. Was that a bad idea?

In a valley near Tromsø, Norway, an antenna has just transmitted a radio signal to potential alien listeners.

This isn’t the usual approach to the Search for Extraterrestrial Intelligence (SETI). Usually, SETI scientists use such antennas to listen, not to speak. They hope to hear a signal from so far away that they would have been broadcast tens, hundreds, or even thousands of years ago. So far, no luck.

The Tromsø transmission is an example of “active” SETI. The idea is simple: send a signal that would alert aliens we’re here, and listen for a reply. The Tromsø broadcast was beamed to one of the nearest star systems believed to have an Earth-like planet. The target is located 12 light-years from our solar system. Since radio waves travel at the speed of light, we’ll have to wait more than two decades before looking for a reply.

While the broadcast from Norway is unlikely to provoke a response by any extraterrestrials, you can be sure it will provoke plenty of Earthlings.

Why is messaging aliens such an issue? To begin with, what do you say to someone you’ve never met, and who’s a member of a different species? Do we tell aliens that we engage in war, threaten our environment, and chow down on other critters? More importantly, could sending signals endanger our whole species? Suppose aliens do exist, and they’re unfriendly. If we draw attention to ourselves with a broadcast — no matter what its content — they might respond with a fleet of interstellar missiles to take us out. Bummer.

Would aliens really do that? Why should we take the chance? Two reasons:

• We’re already making noise. We’ve been broadcasting into space with high-powered transmitters (radar and TV) for more than a half-century now. Sure, those signals aren’t easy to detect out there in space — at least for someone with our level of technology. But for a society a century or two ahead of us, it would be trivial. And if the aliens are not at least that advanced, they simply won’t have those interstellar missiles.
• We shouldn’t silence science. We have other needs for radio signals. To locate comets headed our way from the outer regions of our solar system, for example, we will need to use radars, ones much more powerful than the ones we have today.

Let’s face it, it’s impossible to know what our great-great-grandchildren will find interesting or worthwhile to do.

Personally, I hope the aliens get in touch.

Adapted from "We just beamed a signal at space aliens. Was that a bad idea?” by SETI’s Senior Astronomer Seth Shostak for NBCNews MACH (November 2017).

Listening Triads are an easy strategy for structuring small group reading and discussion. They give students practice in active listening and monitoring their own comprehension as they read.

Divide students into groups of three and give them a text (such as the article in this lesson) to read. During or after reading the text, the members of each group discuss and build understanding of the meaning of the text by acting out three roles: those of questioner, explainer, and recorder.

The questioner asks questions about the text. For example:

• What does that mean?
• Why do you think that is?
• Can you explain what's similar/different about _____?

The explainer uses the text to attempt to answer the questions. For example:

• I think it means that...
• I think what the text says is true/false because...
• This is similar to/different from _____ because...

The recorder keeps the group on-task and records notes on the questions and their answers.

The students can rotate between roles periodically (for example, every three minutes during discussion), so that everyone gets a chance to take on the different cognitive tasks.

Consider with your students the distance that human-made radio signals have travelled at the speed of light (as all electromagnetic waves do).

Show slide 1 (the Sun photographed from Earth's orbit). Ask students to consider the vastness of the universe. Ask them:

How long does it take for light to get to Earth from the Sun?

How do we use distance and speed to calculate travel time?

Calculate the time it takes for light to travel from the Sun to the Earth.

Answer: The Sun is 150 million km (or 93 million miles) from Earth. Light travels at a speed of 299,792 kilometers (or 186,287 miles) per second. It takes 499 seconds for light to travel from the Sun to the Earth.

Ask:

How long would it take a radio wave from our local radio station to reach the Sun?

Possible answer:

Light and radio waves travel at the same speed, so it'd take 499 seconds (or about 8.3 minutes) for a radio wave to reach the Sun from Earth.

Show slide 2 (with images of Moon landing, Mars, Voyager, and Alpha Centauri) to give students a sense of the vastness of the galaxy. Scale up with questions:

• How long did we wait for the transmissions from the Apollo missions on the Moon?
• How long would NASA wait to hear a reply from a rover on Mars?
• How long would NASA wait to hear a signal from the Voyager craft?
  • Fun fact: Voyager is carrying a golden record and travels about than 17,000 times slower than the speed of light.
• How long does it take for light to arrive from Alpha Centauri?

Extension: a nice visualization can be found at Distance to Mars.

One of the points made by the writer of the article is that our electromagnetic signals have inadvertently been escaping Earth and going out into the universe for more than 50 years. Think of broadcasts such as baseball games and music on the radio or television broadcasts. Radio was invented in 1895, and the signals haven't been strong enough to travel any distance beyond Earth until a TV broadcast of the Olympics in the early 1930s.

Show Slide 3 (Milky Way with the captions "200 light years from the Sun" and "2,000 light years from the Sun.") This slide shows a diagram of what SETI scientists call "the radio bubble" since the transmissions leave Earth in three dimensions, like a sphere.

Paraphrase:

Nothing can travel faster than the speed of light.

Remember the picture of the Milky Way? It is 100,000 light years across. How long would it take for any electromagnetic waves to get across our galaxy?

Intended answer:

It would take any electromagnetic waves 100,000 years to get across our galaxy.

Continue paraphrasing:

TV and radio signals bounce around Earth but also beam out into space as electromagnetic waves.

The first strong radio signals on Earth were sent only a little over two centuries ago. On a cosmic scale, they haven't left our backyard. This tiny yellow dot shows how far our accidental signals have reached since we invented radio in the 19th century. The small circle on the right shows how far our signal would have reached if we'd invented radio in the years before 1 BCE. What was happening then? If a civilization were transmitting radio signals then, would we have heard them?

Intended answer:

Two thousand years ago was the time of Roman rule in Europe and the Han dynasty in China. Radio technology was not yet invented, so we would not have heard their signals.

Point out that a radio bubble 10 or even 20 times as big is comparatively small when compared to the size of the Milky Way, and ours is just one of many galaxies in the universe.

Now lead the class in a conversation about whether humankind should transmit messages, or just listen for ones we might receive, or neither. If you do not feel comfortable running a discussion, this question could easily be used as a writing prompt instead of a discussion prompt.

Students may prefer to take one of the three viewpoints as their own. If you expect students will not divide evenly, you may consider randomly assigning them roles or sides in the debate.

Explain to students:

It is your job to argue well for the position you choose (or are assigned). Use information on this page as well as information from the prior sessions. It is also a great time to use your previous notes about waves and the unit's focus words.

For ideas about how to run a class discussion, click here. Consider printing out these Talk Move tips. Take a look at the discussion rubric.

End this lesson with a general discussion during which students share their own comments and raise their own questions.

Image Credit: The Very Large Array of Radio Telescopes by Dave Finley, AUI, NRAO, NSF. NASA Explanation: Each of the 27 radio telescopes in the Very Large Array (VLA) is the size of a house and can be moved on train tracks. The VLA has been used to discover water on planet Mercury, radio-bright coronae around ordinary stars, micro-quasars in our galaxy, gravitationally-induced Einstein rings around distant galaxies, and radio counterparts to cosmologically distant gamma-ray bursts.

This extension gives students a chance to see a real message sent to possible extraterrestrial intelligent life. There is a lot to digest.

Another famous active SETI project is 1974's Arecibo message. It contains three minutes of binary data beamed to a specific location 25,000 light years away.

The binary code is shown (the string of 1s and 0s). The code represents 1,679 pixels in a 23x73 array.

Image Credit: Frank Drake (UCSC) et al., Arecibo Observatory (Cornell, NAIC)

If you'd like, you can give time for students to reconstruct the Arecibo message on the graph paper in the printable below. They may not gain much from this task, however.

Look at the black and white image together. Ask students to figure out what they are looking at before you give them clues about what they're seeing. Ask:

Can you make sense of Arecibo's encoded message to the universe?

Engage students in a conversation about what they see in the image, if anything. The images are fairly abstract, so you will want to point out parts that are supposed to be specific things. You can do this by projecting the image onto a white board and coloring in squares.

The pixelated images represent the numbers 1–10 (top of image); atomic numbers for five common elements (pink at the top) and formulas for sugars and bases (green); DNA (blue); the human form (red); Earth's location in the Solar System (line of white just below the human) indicating which of the planets sent the message (slightly higher third dot); and the radio telescope that sent the message (pink at the bottom).

End the session by asking students what they would send in a message to other civilizations.

This extension is a chance to see how well the students can communicate their reasons for what they read in the message and what they would send in a message. Give students time and space to discuss and design their message, or to write about what they would send and why.

TERC has an interesting activity related to the Arecibo message in its Astrobiology Afterschool curriculum: Activity 1.2, "Is Anybody Out There?"

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