Guest blog: Bucket List Astronomy Class: Revisiting Einstein

Posted by Nicole Kiefert
on Wednesday, August 23, 2017

By Jacob Ackman and Remy Shelton 

The basic idea behind gravitational lensing. Objects in the background appear to be deflected slightly 'outward' from their true positions. This can be extreme when the intervening object is something like a galaxy cluster, or it can be extremely subtle, when the intervening object is something like the Sun.
At our camp, we heard from Dr. Don Bruns, a retired physicist who is taking it upon himself to finish an experiment that has not been successfully reproduced since 1919: Observing the bending of starlight during a total eclipse.

Bruns discovered a passion for astronomy at an early age. In high school, he was performing his own research projects, keeping up to date on astronomical topics by reading magazines and networking with others in the field.  In 1969, he built a telescope with his twin brother in high school, and has had nearly 50 years of telescope and field work to prepare him for this eclipse.

As we’d learned earlier in this class, gravity does weird things to light. Black holes warp space so much that you can literally see what’s behind them. But even with less massive objects, Einstein’s theory of relativity predicts that the starlight will bend as it passes by, making the stars look like they’re out of place. In 1919, an expedition led by Sir Arthur Eddington set out to test Einstein’s theory, which was competing against Newton’s law of gravitation. Although both theories suggested that the stars near the Sun would appear out of place, Newton’s predicted deflection was only half Einstein’s, which predicted that stars near the Sun would appear to be about 1.75 arcseconds out of place. This phenomenon would only be able to be observed during a total solar eclipse due to the Sun washing out the light from other stars. This first experiment was successful, but Eddington observed only a handful of stars. Still, it was enough data to show that Einstein was right, and this verification is what launched Einstein to fame.

The 10 November 1919 New York Times of November 10, 1919, engaged in a bit of hyperbole, but this expedition launched Einstein to celebrity status.

Naturally astronomers wanted to get better results, so In 1922, they performed a second experiment in Brazil. The results were not quite so neat. Gravitational lensing will cause all of the stars to appear deflected away from the sun, but instead the results showed the stars deflecting in every direction, even sideways and towards the Sun. Fortunately the average reading of these stars fit the predicted curve close enough that scientists worldwide declared Einstein’s theory was still correct.

In the early experiments, most of the issues came from getting a ridiculously accurate calibration of the angles on the photographic plates, something known as the plate scale. The first experiments took the scale from measuring the distance between 2 stars and dividing the known angular separation apart by their physical separation on the negative. The problem came from trying to figure out a scale from objects that were out of place, so the scale was not very accurate. To fix this problem they decided to take a calibration picture after taking the picture during the eclipse. The first attempt to do so was in 1922 in Australia, and the results were…. Not so good. Several factors gave them an uncertainty of +/- 33%, which isn’t even good enough for our introductory labs.

So scientists tried again in 1929 but the telescopes tube was so long that it warped during the movement to take the calibration image. Undaunted, they hatched another idea to use a double exposure negative using a beam splitter, giving them the calibration image and the eclipse image simultaneously. They tried this four times – in 1936, 1947, 1952, and 1954 – and each attempt led to new and improved difficulties. In 1936 the operator pointed the telescope at the wrong stars for calibration. In 1947 the red filter that was used in conjunction with the beam splitter warped due to the humidity. To fix this problem in 1952 they pointed a fan at the filter, but the images became distorted due to too much wind. The final attempt was in 1954, but the sky was too cloudy at their location to take the observation.

The special concrete base underneath Dr. Bruns' telescope depicts the star field behind the Sun during totality. // Ph​oto credit: Samuel I. Beard, Jr.
Desperate, astronomy publications pleaded with future astronomers to attempt the experiment again. The most recent one was in 1973 – 44 years ago! And that one failed, as well. The plate holder for the negatives was held up by springs to allow the observer to change the plates rapidly. Tragically, the springs were not strong enough, so the plate lost contact with the camera when they shifted the camera to take their plate scale image, throwing the image off and yielding the same sorry results as the 1922 experiment.

Since then, no one has tried to recreate this experiment during a total eclipse. The effect has been observed, however, as radio astronomers observed quasars and verified relativity’s predictions to 0.01%.

But all this could change.  Dr. Bruns wants to successfully recreate this experiment so that the work of all the astronomers before him could be completed and their work not be in vain. He has multiple advantages over the astronomers of previous eras. For instance, in 1922 the crate for the photographic plates alone weighed over 600 pounds and tons of equipment had to be shipped to the observation point well in advance. Now, in 2017, Bruns can fit all of his equipment in the back of his car and everything is computerized, which allows him to perform the observation solo, rather than with a crew of people. Also all of his equipment is commercially available, and several companies have generously lent him equipment to use for this experiment. Tele Vue Optics in New York has provided the telescope – a NP101Is, which has a wide field of view with pinpoint star images. Finger Lakes Instrumentation in New York has donated a ML8051 Monochrome CCD camera for the experiment. Software Bisque in Colorado provided a tripod. He then selected an 8000-foot mountaintop near Casper, Wyoming to take his data to maximize the chance of clear skies and minimize the atmospheric effects.

Dr. Don Bruns poses next to his gear just 20 hours before totality. // Photo credit: Samuel I. Beard, Jr.
He has done plenty of dry runs with this equipment so that everything runs smoothly during totality. In March 2017, he took a calibration test of stars, expecting a straight-line result, as there is no deflection. He got the result expected within 0.03 arcseconds, a phenomenal improvement on previous observations. Moreover, there are two fairly bright stars that will appear very close to the Sun during the eclipse, and they should appear to move all of 2.2 arcseconds. This result from these two stars alone will be enough to prove Einstein right because they are so close to the sun that it will move more than 1 pixel across his image. Within an hour he will know if the images are good enough to get the results he’s hoping for, but it will still take him several weeks to process the images to get the final results which will then be published about 6 months after that, so keep on the lookout. The BLAsT Class wishes Dr. Bruns the best of luck in his experiment, and we look forward to seeing his results!

UPDATE from Dr. Bruns 08/24/17: 

"I finally did complete the experiment the astronomers were hoping for. I got perfect focus, perfect exposure, perfect timing, and no wind or clouds. I am still over the moon!" 

To leave a comment you must be a member of our community.
Login to your account now, or register for an account to start participating.
No one has commented yet.