Can you find Pluto?

This is a scan of a photo of the original images that Clyde Tombaugh used in 1930 to discover Pluto. The photo came from a personal visit to the Lowell Observatory in Flagstaff, Arizona, where Dr. Tombaugh made his original discovery many years ago. The observatory maintains an excellent website--teachers might especially enjoy looking at the StarTales images which are posted regularly and would provide a daily astronomy fact for their students.

Clyde Tombaugh made his original discovery using a blink comparator--a mechanical device that flips between two images. By "blinking" between two images of the same portion of the sky, the observer can look for an object like a planet or a comet that moves in relation to the background of stars over the course of successive nights. This is exactly what Clyde Tombaugh did with the images above to find Pluto.

You can "flip" these same images in this web page. Use the slider below to see the portion of the sky in which Pluto was discovered. On January 23, 1930, the planet is in one location. On January 29, 1930, it has "wandered" or moved to another location in relation to the stars. Use the individual frame buttons to see each image one at a time.

Note: It can be a challenge to find Pluto, in part because the two photos were shot at different exposures so different stars are visible on each one. Clyde Tombaugh faced this same challenge, though he was an expert at viewing these images and was quite comfortable with the differences in exposures.

When I have done this with elementary and middle school students, I have left the images for a week or so for their investigation. Students are then asked come to a consensus about which object is Pluto. Then I show them the "arrow stack" which points out where Pluto is located

You and your students could also use public domain image processing software to open and "flip" these same images. Download the software:

ImageJ (Java based software that runs on Mac, Windows, or Linux systems)

Then download the same images as shown above, except this time in TIFF format. These image "stacks" can be "flipped" using the < > keys on your keyboard once you've downloaded the software and the images. Click and hold on these links in your browser--then download them to your desktop.

Pluto stack as a TIFF image
Pluto stack "arrow"
- Additional challenge--can your students locate where in the first Pluto stack I "erased" out the arrows that are found in the second stack?

Further reading:

For more information about Pluto and its discovery, try this excellent site about Pluto maintained by the Planetary Space Physics homepage at the University of Colorado.

Here's another site that challenges students to find Pluto from a much more recent image. This site is hosted by the Adler Planetarium. It includes a terrific discussion (with excellent images) of planets as wanderers.

Pluto and Charon: Ice Worlds on the Ragged Edge of the Solar System by Alan Stern and Jacqueline Mitton is an excellent book about the discovery and current investigations into Pluto.

Clyde Tombaugh and the Search for Planet X is an excellent book for elementary students about the discovery of Pluto.