Tour of the Galaxy

Duration: 2.5 minutes
Grade Level: 3rd-5th
Next Generation Science Standards: 5-ESS1.A; Using Models; Obtaining, Evaluating, and Communicating Information; Analyzing and Interpreting Data; Engaging in Argument from Evidence

This resource was developed through WGBH’s Bringing the Universe to America’s Classrooms project, in collaboration with NASA.

• Before students engage with the media, have them consider what they think they would see if they were to fly in a spacecraft to the edge of the galaxy. Have them write or sketch a flight path, starting with their takeoff location on Earth. You might ask them to consider scale, specifically Earth’s place within the solar system and the larger galaxy.
   
• Have students watch the video twice. In the first viewing (note: the video is not narrated), students will get a gist of the content. In the second viewing, students can record observations and scientific questions about the content.

• Use the Your Cosmic Address slideshow to scaffold students through creating a diagram showing the relative scale and location of some objects found at each scale, starting with their town or city and expanding out to the galaxy. 
   
• Students may use the data on sizes provided in the slideshow to create an infographic comparing objects at each scale, beginning with the United States and ending with the Milky Way.
   
• Can they develop and express an argument about the scale of the galaxy using evidence from their graphic?

Earth may seem like a large place. People cannot easily cross the globe to explore different lands and sail from ocean to ocean. But zoom out past the atmosphere, and Earth soon begins to look small relative to the vastness of space and the many objects found in it.

Within the solar system, conventional units, such as miles or kilometers, can be used to describe distances. However, space is so expansive that it is not practical to use those units. The numbers would be too long! Instead, we use a light-year, or the distance that light travels in one year (about 5,880,000,000,000 miles or 9,460,000,000,000 kilometers). Several labels throughout the video show the viewer’s distance while traveling away from Earth using light-year units. For example, the label “Distance from Earth: 1 Light-Hour” appears at about 1:03, along with a view of several planets orbiting the Sun. That distance conveys that it takes 1 hour for the Sun’s light to reach that location. As the video continues, the viewer is taken beyond the orbiting planets of the solar system and through interstellar space to more than 10,000 light-years away from Earth.

The video at 1:23 shows the Sun’s true brightness compared with other stars within the galaxy that are visible from that location. Here, the Sun appears much larger and brighter than the other faraway stars, which look like tiny dots. As the distance continues to increase, the Sun appears smaller and less bright, until it fades from view at about 1:47.

In addition to the presence of space telescopes and probes (Voyager 1 being the farthest out; see 1:18 “The trajectories of our farthest spacecraft”), humans have created a footprint in space in the form of radio signals. The video at 1:54 shows a blue sphere that visually represents the limit of humanity’s strongest radio signals. The first radio signals strong enough to escape Earth’s atmosphere in the late-1930s have traveled fast and far, creating a radius of nearly 80 light-years. But even that distance, which is far beyond where our spacecraft have traveled, is a tiny fraction of the distance across the galaxy!

Far outside our solar system but within the Milky Way, other stars with known planets come into view (1:58). Here, it becomes clear that our solar system is just one of countless star systems. Statistical estimates suggest that each star in our galaxy has an average of one planet. That would mean our galaxy has about 1 trillion planets! The first exoplanet was discovered from an observatory in France in 1995. From that point, the search for more extrasolar planets took off. More than 3,700 exoplanets have been discovered. NASA has a few space telescopes, like Kepler, constantly scanning patches of space for distant planets.

As students observe images and read about the journey from North America to the edge of the Milky Way, they can begin to form a mental map of Earth’s place in the galaxy. They will also be able to expand their U.S. address into a cosmic address.