Constructing the Light Curve

Teachers Explore How Light Curves Uncover the Mysteries of Asteroids

March 19, 2011
By Margie Corp for Stars at Yerkes News

What do spinning potatoes have in common with asteroids?  On a recent trip to the delightful dark skies of southeastern Illinois, teachers were challenged to uncover the meaning of asteroid light data as well as build a model of a rotating asteroid, using a potato as an extraterrestrial substitute. 

The workshop was organized by ARCS teacher Kathleen Roper and was held on the campus of Eastern Illinois University, in Charleston, Illinois.  During the evening sessions, teachers were treated to a tour of the Astronomical Research Institute facilities by Bob Holmes (aka Supernova Bob).  All participants were astounded by the impressive array of telescopes, including the 24 inch telescope and the recently refurbished 30 inch telescope.  The 30 inch telescope, funded in part by Hands-On Universe, is scheduled to join the Skynet network of telescopes for student research projects. 

Bob Holmes describes the capabilities of the 30 inch telescope to Stars at Yerkes teachers.

Bob Holmes ended the tour with a preview of his latest project. The 1.3 meter (50 inch) telescope currently is being constructed at ARI.  The fork of this telescope weighs nearly a ton, and the telescope is planned to be completed this summer.  Bob continues to inspire teachers and students alike by providing access to a rich library of data on asteroids imaged at ARI.

Teachers illustrate the size of the fork of Bob Holmes' newest 50 inch telescope.

Tyler Linder, a graduate student at Eastern Illinois University, was the featured instructor for the sessions at EIU .  Tyler first guided teachers through a discussion about photometry (see attached presentation below).  Using data from ARI scopes, Tyler then instructed participants how to use computer software to organize light data from asteroids to calculate the period of asteroid rotation.  As seen in the photo at left, one asteroid rotation can have several peaks of light intensity, due to the topography of the asteroid.  Each point on the graph represents an image taken by the telescopes.   Dr. Jim Conwell, also of Eastern Illinois University assisted participants in understanding this wealth of information.

Tyler Linder explains the period of asteroid rotation..

At right, Rich DeCoster and Dr. Jim Conwell examine data.

ARCS teacher Kevin McCarron provided teachers with the opportunity to assemble a model to simulate asteroid motions.  The motorized device, nicknamed the "Spud Spinner," held a potato on the prongs of a rotating base.  As the potato rotated,the light that was reflected from the changing topography of the potato was measured by a light sensor, also designed by Kevin.  Readings were collected using a multimeter.  Teachers were prepared to demonstrate to their students the motions of asteroids, so that students should be able to visualize the complexities and limitations of data taken from an Earth-based point of view.  The Stone Edge Observatory was also highlighted as another source for collecting asteroid data.

Kevin McCarron demonstrates the "Spud Spinner to Laura Toennies and Kathleen Roper.

Potatoes and asteroids may not have much in common, but the fascination for learning more about objects beyond Earth and those who pursue that knowledge share a special bond, as was demonstrated this weekend.

Learn more about the work of Bob Holmes and the Astronomical Research Institute at:

Marc Berthoud,
May 8, 2011, 9:19 PM