### Measure the universe

**Directions for teachers:** After students have had a chance to read “Kuiper belt dust may be sprinkled in our atmosphere,” use these discussion prompts to help your class think about the scale of the solar system and universe — and how scientists study phenomena that are hard to reach in space or very distant in time. If you include the bonus prompts listed under No. 1 and No. 2 below, be sure to give students time to do rough calculations, using pencil and paper or a calculator as necessary.

**1. Kuiper Belt Distance in Context**

The Kuiper Belt extends from roughly 30 astronomical units (4.5 billion kilometers) to 55 astronomical units (8 billion kilometers) from the sun. It’s challenging to fathom such immense distances, but we can try. Ask your students to call out known distances that might be more familiar. What about distances that might be comparable? How do these distances compare with the distance to the Kuiper Belt? How do these distances compare with the width of the Kuiper Belt? (Note that the Kuiper Belt’s width is an impressive two-thirds the distance from the sun.) Which of your comparisons are most helpful in imagining great distances and why?

*Here are a handful of distances that students might consider:Length of an American football field, ~0.1 kilometersHeight at which planes fly, ~10 kilometersEarth’s circumference, ~40,000 kilometersDistance from Earth to the moon, ~380,000 kilometersAverage distance from Earth to Mars, ~225 million kilometers*

Bonus prompt: Another way to imagine distance is to think about hypothetical travel time (ignoring for these purposes, the logistics of fuel and the potential hazards of space travel). Give students time to calculate how long it would take to get to the Kuiper Belt and other astronomical destinations they might mention assuming travel by car (100 kilometers per hour), space shuttle (28,000 kilometers per hour) or at the speed of the Voyager probes (56,000 kilometers per hour).

**2. Our Galaxy and Universe**

Of course, the Kuiper Belt is still within our solar system; the sun’s influence extends roughly 120 astronomical units (18 billion kilometers). Without using additional resources, ask students to predict how close the nearest star other than the sun is? What about the nearest spiral galaxy? How do those distances compare to the distance to the Kuiper Belt? What about the width of the observable universe?

*The nearest star other than the sun, the binary pair known as Alpha Centauri, is ~40 trillion kilometers (4.0 x 10 ^{13}) from Earth. The nearest galaxy (that is not a smaller, companion galaxy) is the Andromeda Galaxy at ~24 billion billion kilometers from Earth (2.4 x 10^{19}). The diameter of the observable universe is thought to be 880 billion trillion kilometers (8.8 x 10^{23}).*

Bonus prompt: Ask students to make an analogy that expresses two of these astronomical distances in terms of two more familiar distances. For example: If the distance from Earth to the Kuiper Belt were the length of a football field, the distance from Earth to the nearest galaxy would be…? Students can use pencil and paper or calculators depending on how rigorous you’d like the answer to be.

**3. Approaches to Studying Astronomy**

The article “Kuiper belt dust may be sprinkled in our atmosphere” describes one way that scientists are studying astronomically distant realms — by studying debris that might travel from there to here. Apart from space rocks and dust that arrive at Earth, how else can astronomers explore places that are too distant to visit in person? Encourage students to draw on examples they might have heard of and to use their own logic. What kind of information can astronomers glean through each of these approaches? What are the benefits and what are the limitations?

*The most obvious answer is that astronomers use visible light and other forms of electromagnetic radiation to study these distant places. Students might also know that researchers are monitoring gravitational waves, or ripples in spacetime (see Making Waves Educator Guide). And we have sent some probes to distant reaches of the solar system, including the Voyager probes, which have traveled to the edge.*

**4. Beyond Astronomy**

In what other fields of science do researchers study distant, hard-to-reach phenomena? What makes it hard for researchers to study these phenomena directly? What approaches and technology do researchers use and what challenges do they face? How is the work similar to or different from that of astronomers studying the distant reaches of the solar system, galaxy or universe?

*Students might point to deep-sea explorers who use tidal motion to make inferences about ocean depth, sounding weights to collect samples, sound waves, seismographs and crewed and autonomous submersibles. Or, students might think of geologists who use seismic waves and cores to study the structure of the Earth’s interior. Doctors use probes and scopes to see inside the human body, and researchers are exploring how to deliver drugs using nanotechnology. Computer simulations are also helpful in trying to understand distant and unreachable phenomena. To study Earth’s upper atmosphere, scientists use balloons carrying specialized instruments, as well as planes. And scientists use lidar to try to understand inaccessible forested environments from above.*

**5. Drawing Parallels to Distant Times**

Ask students what parallels they can draw between the efforts, techniques and experiences of scientists studying distant reaches in space to those who study the ancient past. Encourage students to use specific examples in their brainstorming. Is studying faraway places easier or harder than studying the distant past and why? Are students more interested in one or the other and why?

*Archaeologists, paleontologists and paleoclimatologists all use records found in or on Earth to try to reconstruct the past. Archaeologists examine artifacts to try to understand how people lived, while paleontologists use fossils to study the evolution of other life-forms. Paleoclimatologists want to understand current and future climate by studying fossils, tree rings, ice cores, how sediments have built up overtime, and so on. Students should consider that any scientific field interested in how things are in the present can benefit from a deeper understanding of how things were in the distant past.*