Dry Lab Activity

Unit C - Chapter 7

Investigating Science 9

Inquiry Activity

How Far is That Star?

Skills Reference 2

Skills you Will Use

  • Using appropriate equipment and tools
  • Drawing conclusions

In modern times, high-tech imaging equipment and computers do most celestial mapping. However, for most of history, astronomical mapping and measuring was done with telescopes, simple mathematics, and a phenomenon known as parallax.

It is interesting to note that even though equipment and technology has become much more sophisticated, the calculations involving parallax have remained the same. Astronomers require two perspectives of celestial objects to gain depth perception. For example, images from NASA's Spitzer Space telescope were combined with astronomical images from Earth to provide very accurate parallax calculations for the distances to many stars, galaxies, and other celestial objects.

In this activity, you will use the phenomenon of parallax to make a calculation of distance to an object. You will also compare this calculation to the actual distance to assess the accuracy of your parallax calculations.


How can parallax be used to determine distances to stars?

Materials and Equipment

  • masking tape
  • black and red pencils
  • a lamp with a 100-W bulb
  • a copier paper box with no lid
  • paper clips
  • metric ruler
  • paper
  • calculator

Dry Lab

A "dry lab" activity includes collected data and/or a video solution for your convenience. You can simply watch the following video and use the provided data, or if you wish to perform this lab for yourself, follow the procedure steps 1 through 16 described in the video. The same steps are included in written form in the documents available for download on the bottom of this page.

Analyzing and Interpreting

  1. A student performing the procedure steps 1 through 16 recorded the following results.


    Parallax shift (mm)

    Focal length (mm)

    Diameter of Orbit (mm)

    Calculated distance to star (m)

    Actual distance to star (m)
















    Calculate the distance to each star using the following formula. Do your calculations make sense in terms of the actual distances to each star? If you made your own experimental measurements, do the calculations for your numbers as well.

  2. If there is a difference between the calculated distance and actual distance to the stars, explain why the difference exists.

Forming Conclusions

  1. Can parallax be used to determine the distance to actual stars? Explain how the technique used in this investigation could be adapted and applied to determining the distances to actual stars.