Sky and Telescope - August 2018 - 24

Testing Relativity

p THE BIG DAY The author (left) prepares on the morning of the eclipse. The tripod is bolted to a cement base topped with a commemorative mosaic eclipse design built by Steve Lang, which features the Sun, inner corona, and stars. A group (right) assembled at Lions Camp to watch the eclipse.

The Winning Formula
The key to success in this experiment was to plan ahead and
practice - something every amateur astronomer already
knows to do when attempting to image a transient event. I
did everything I could ahead of time, from verifying electrical
power when the lights were turned off during totality to bolting the tripod legs to a concrete base so the polar alignment
would not accidentally change. My site was in a grassy ﬁeld
protected by tall trees, so there was no wind at all.

Does the Sky Change
During an Eclipse?
After watching the total solar eclipse of
1715, Edmund Halley reported seeing
the sky become bluer near totality. Was
that an optical illusion or reality? Modern
observers have since measured the sky's
color and brightness during eclipses,
but they typically use photometers that
integrate over the entire sky. I wanted
to collect data, resolved over time and
angle from the Sun, to determine just
24

AUGUST 2 018 * SK Y & TELESCOPE

I followed a detailed checklist, too. For example: "Remove
solar ﬁlter." I didn't want to forget anything in the excitement leading up to totality.
On two nights before the eclipse, I was able to perform a
good polar alignment and take calibration images. I left the
telescope and camera setup untouched for four days, with
a little guard fence around it. Since all of the visitors knew
what I was doing, they left it alone. In fact, there were a few
other telescopes set up early around the camp, and no one
had any problems.
On eclipse day, I had a weather station set up to record
temperature, pressure, and humidity, so I could correct for
atmospheric refraction. I also had the software play a chime
after each exposure during the experiment. Hearing this
every few seconds was comforting and allowed me to enjoy
the spectacle with family and new friends.
I started the detailed image processing back home in San
Diego. Looking at the images, I could see all the stars that
I was hoping for and more. I had decided on my procedure
ahead of time, and modern software helped me complete all

how significantly the sky's appearance
would change.
My twin brother, Don, recruited me to
join him and conduct this experiment
while he focused on light deflection. The
equipment was compact and easy to set
up at my site near the eclipse centerline
in Esterbrook, Wyoming. I attached a
wide-field (70° FOV) lens to an SBIG STi-C camera with built-in RGB filters and
mounted it to a Meade equatorial drive
fitted with an occulting disk. The disk
allowed me to take sky photos before,

p SKY SETUP Ronald Bruns, the author's
twin brother, used a wide-field lens on an SBIG
ST-i-C camera to measure the sky's color and
brightness before, during, and after totality.

THE BIG DAY (2): STE V E L A NG;
SK Y BRIG H TNESS SE T UP: RON BRUNS

Just for this experiment, the manufacturers graciously
loaned me a Tele Vue-NP101is apochromatic refractor, a
Finger Lakes ML-8051 CCD camera, and a Bisque MyT Paramount ﬁeld tripod. I already owned a MyT mount. With help
from my cousin Steve Lang, I chose to set up a week early
at the Lions Camp near Casper because of the high altitude
and prospect of clear skies. On eclipse day, the camp hosted
visitors from around the world, from England to Latvia and
New York to Texas. We all thoroughly enjoyed the eclipse and
celebrated together after totality.

Sky and Telescope - August 2018

Table of Contents for the Digital Edition of Sky and Telescope - August 2018