“Give me six hours to chop down a tree and I will spend the first four sharpening the axe,” Abraham Lincoln is quoted as saying.
The Colorado College Physics Department’s variation on that might well be “Give me a 2½-minute solar eclipse and I will spend weeks beforehand preparing for it.”
CC Physics Professor Shane Burns is working with a group of students in advance of the Aug. 21 eclipse, the first total solar eclipse visible in the contiguous U.S. in nearly four decades.
Colorado College students Ben Pitta ’18, Maddie Lucey ’18, Jake Kohler ’18, and Nick Merritt ’19, along with Physics Department Technical Director Jeff Steele, will depart for a remote area outside Lander, Wyoming, about a week before the eclipse, where they will attempt to reaffirm one of the findings of Einstein’s general theory of relativity: that is, that the path of light is bent by massive objects.
They will use a CCD (charge-coupled device) camera and an 8-inch aperture telescope in an effort to measure the curve of light from stars during the eclipse. Burns says the effect is small, less than two arc-seconds, or approximately the width of a human hair viewed at 10 meters.
In 1915 Einstein predicted that this bending should be measurable during a solar eclipse; the effect was first measured by Arthur Eddington during an eclipse on May 29, 1919.
In preparation for the event, Pitta, a physics major with a concentration in astrophysics, is developing sun-tracking software to determine the exact patch of sky they will be imaging and which stars will be visible during the narrow timeframe allotted by the eclipse. The difficulty is compounded by the fact that the stars will be behind the sun, and thus very faint.
Burns and Pitta have been testing the CCD and telescope system, developing software to process the images, and finalizing an observation plan.
“The position of the sun during the eclipse depends on where you are on earth,” Burns says. Pitta’s program will determine the position of stars behind the sun and the exposure times they should use so that the stars can be imaged accurately during the crucial 2:20 minutes of the eclipse. Pitta is conducting trial runs to make sure the camera is pointed at the precise location in the sky, the exposure times are correct, and the procedures are well established. “We want to have everything in place so that we can effectively take observations,” Pitta says. Because the window of observation is so short, they will have to be efficient and well-practiced.
Einstein theorized that as light rays from stars pass near the surface of the sun during an eclipse, they should be bent. “This makes the stars appear to shift relative to their positions when the sun rays don’t pass near the sun,” Burns says. “In order to measure the effect, one compares the positions of stars whose rays graze the surface of the sun to the positions of the same stars when the sun is in a different position.
“Of course,” he adds, “you have to wait for an eclipse to see stars near the sun.”
Despite the drills and trial runs, Burns says that realistically, things can go awry. The students might not be able to access the remote area they hope to. Other glitches may arise at the last minute, with the students needing to redo the calculations on the spot.
“There’s not much time to figure it out on the fly,” says Burns.
“There’re always problems that arise, and you need to find the path to take to solve them,” Pitta says. “That’s physics in a nutshell.”
The team will be conducting the observations and imaging on their own, as Burns will be presenting a (sold out) program for CC alumni near Grand Teton National Park during the eclipse.
To measure the bend of light, the students will image the same patch of sky six months later, and if successful, should be able to detect a subtle shift of stars. If so, the experiment will bear out Einstein’s prediction that light does not always travel in a perfectly straight line. While traveling through space time and nearing the warp induced by an object’s gravitational field, light should curve — but not by much.
“It’s going to be a difficult project,” Burns says. “I give the odds for success about 50 percent, but the students will learn a lot.” If successful, Burns and the students plan to publish the results in a scientific journal.