Download Part I: Modeling Light Years - The “Student

Light Years
Earth and Space
Part I: Modeling Light Years - The “Student-Minute”
A light year is the distance light can travel in one Earth year. It is a defined unit based on the speed
of light. Light years are units that allow us to measure and discuss extremely long distances, but
the concept of a light year can be modeled and used for short distances as well.
1.  In the area, mark the starting spot with a piece of masking tape and label it “Start.”
2.  Beginning at the "Start" marker, have one student volunteer walk heel-to-toe in a straight line
for exactly one minute. Use the timer to make sure your time is accurate
3.  Mark the spot where the walker stops with a piece of masking tape.
4.  Measure and record the distance traveled during the minute (from the “Start” marker to the
masking tape). In the Student Journal, record this distance in the data table for Trial #1.
5.  Repeat steps 2-5 two more times for a total of three trials.
6.  Calculate and record the average of the three distances.
Part II: The Speed of Light
A beam of light from the Sun or from a flashlight travels at 300,000 km per second. This is known
as the speed of light. Nothing in the known universe travels any faster than light. Let’s do some
calculations to determine how far light can travel in a year.
1.  Complete Chart 1: Calculation of the Distance Traveled by Light in One Year in Part II of your
Student Journal. The numbers used are too big for a calculator, so you will have to do them on
a piece of scratch paper.
2.  Compare your answer to your teacher’s answers.
Speed of Light = 300,000 km per second
Please complete Part I and Part II in your Student Journal.
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Light Years
Earth and Space
Part III: Calculating a Light Year
The huge distances between objects in space are really big numbers and difficult to work with! If
you were an astronomer, would you like to have to use these numbers every day? Probably not!
That’s why astronomers came up with a new unit for the distances in the universe. Astronomers
don’t use kilometers or miles for distances – they use the unit, light year (ly). A light year is the
distance light travels in an Earth year, so it is a measure of distance. This can be confusing, since
a year is a measurement of time. Astronomers also use light-seconds and light-minutes. You
determined the distance of a “student-minute” in Part I, and you will use that model now to
determine the length of a “light-year” in space.
1.  Your teacher will review with you how to use the zeros cancelation method.
2.  Complete the calculations in Part III of your Student Journal.
3.  Compare your answers with your teacher’s answers.
Part IV: Time through Travel
Stars are millions and millions of kilometers away from Earth. For us to see a star’s light, it has
been traveling a long time. Proxima Centauri is 4.2 light years away from us. That means its light
has been traveling for 4.2 years. If Proxima Centauri exploded three years ago, then we would not
see the explosion for another 1.2 years! So, in a sense, when we look at the stars, we are looking
at the past. We have accomplished time travel!
Complete the Chart titled: Are We There Yet? in Part IV of your Student Journal. Part of the chart
has been completed for you. Then answer the remaining questions in your Student Journal.
Part V: Sizes in Our Universe
Astronomers use light years not just to measure distances to objects, but also to describe the size
of the large objects in the universe, like galaxies. For example, we know that our galaxy, the Milky
Way, is 100,000 light years across. That means it takes light 100,000 years to travel from one end
to the other.
Use the data table in your Student Journal to answer the questions about sizes in our universe.
Complete Part III, IV, V and the Reflections and Conclusions in your Student Journal.
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