Introduction
How do astronomers determine how far a star is from the earth? Do they fly out into space with a tape measure??
Astronomers measure the "parallax" of nearby stars to determine their distance from the earth.
Imagine that you could travel to the stars at the speed of light. To travel from Earth to the sun would take about 8 minutes!
The next nearest star, Proxima Centauri, would take us 4.2 years to reach at the speed of light! But what does "the speed of
ilght" mean and how do you use parallax to determine distance? Complete this webquest to determine the answer to these
questions.
Task
Go to the "Process" page, read the directions, view the websites, and answer the questions. After you complete this webquest, you will be asked to show how parallax and light-years are related to each other. You may do this in writing or by drawing a diagram.
Process
Distances on Earth's surface are often measured in kilometers. However, distances to the stars are so large that kilometers are not very practical units. Astromoners use a unit called a light-year to measure distances between the stars. A light-year is the distance that light travels in one year, about 9.5 million million kilometers.
A light-year is a unit of distance, not time. To help you understand this, consider an everyday example. If you bicycle at 10 kilometers per hour, it would take you 1 hour to go to a shopping mall 10 kilometers away. You could say that the mall is "one bicycle-hour" away.
A. Read the following questions, watch the YouTube video below them and then answer the questions on your own paper:
1. How far does light travel in one second?
2. How long does it take for light to travel from the moon to the Earth?
3. How long does it take for light to travel from the sun to the Earth?
4. When we look at the star Proxima Centauri, when did the light we see actually leave the star?
5. When we are talking about the stars, is it possible to 'see the past'? Please explain your answer.
6. Do we have any ways of 'seeing' the past of our own lives? Please explain.
7. Does the light from a star ever stop traveling in outer space? What do you think? Be ready to discuss this question with the class.
Video about light-years:
B. Go to the following astronomy dictionary and read the definition of the word "parallax". Hold your thumb up and do the thumb experiment that it tells you about.
http://www.kidsastronomy.com/dictionary.htm#p
C. Watch this YouTube video about parallax & answer these questions:
8. What shape helps us measure the distance to stars using parallax?
9. The stars appear to shift back and forth as our planet does what?
10. The farther away a star is the ________ it appears to move. (more? or less?)
Evaluation
D. Connect the concepts of light year and parallax. How is parallax related to light year? Explain in writing or create a picture to explain.
Conclusion
This webquest has helped you become familiar with the concepts of light-years and parallax. If you want to do more reading
about these topics and others related to space, check out the following websites:
http://www.nasa.gov/home/index.html
http://www.sciencelearn.org.nz/
http://www.atlasoftheuniverse.com/index.html