SkyandTelescope.com September 2014 31At 6:25 p.m., he was elated to see sunlight inside his
house. Looking outside, he saw the Sun through a small
break in the clouds. He didn’t think the break would last
long enough to set up his telescope again. Fortunately,
he had a 400-mm telephoto lens with a solar fi lter. He
quickly attached them to his DSLR and rushed out-
side. There were only intermittent breaks in the clouds
through which he could take images before clouds again
covered the Sun for the remainder of the day. A transit
line for Richard was not to be, but he was thrilled to have
seen and captured some images of the transit.
Rod carefully packed his equipment in padded cases
for the trip to Maui. On June 5th, he and his wife, SuEllen,
drove to the summit of Haleakala ̄ and set everything up.
Although much of Maui was overcast, skies at the
summit were crystal clear. But winds gusted to 50 miles
per hour! Rod hung his tripod case beneath the mount
and fi lled it with lava rocks to prevent his telescope from
being blown over. At ingress and egress, he observed the
black-drop eff ect that thwarted Captain Cook and other
observers in prior centuries. Both black-drop eff ects
lasted about a minute. Rod also measured the diameter
of Venus’s disk as 58 arcseconds using a crosshair reticle.
The expedition was a great success, capturing the entire
transit on hundreds of images.Mathematical Machinations
After the transit, we compared our photography logs.
Despite the fact that the times of Richard’s photographs
were dictated by cloud breaks, DSLR time stampsindicated that seven were taken within seconds of three
images taken by Rod. Therefore, it would still be possible
to calculate the distance to Venus and the a.u. using the
more diffi cult technique of directly measuring the paral-
lax of Venus’s disk.
GPS devices determined the latitudes and longitudes
of our West Richland and Haleakala ̄ observing sites with
an accuracy astronomers of prior centuries could not have
imagined. Richard used the GPS coordinates in a mathe-
matical model that compensates for Earth’s slightly oblate
shape to precisely calculate the through-the-Earth base-
line distance between us, including a contribution from
Haleakala ̄ ’s nearly 2-mile elevation, as 2,670.453 miles.
When Richard took his images, West Richland was near-
ing Earth’s western limb as viewed from Venus and the
Sun. That would result in some apparent foreshortening
of the baseline distance. Further trigonometric calcula-
tions indicated a foreshortened baseline of 2,213.197 miles.
Rod upsized Richard’s images to match and align
the Sun’s disk to that in his images. Sunspots provided
good reference points for rotating Richard’s images.
The aligned images were put in the Layers Palette in
Photoshop with Rod’s image as the upper layer. Applying
the “Diff erence” Blending Mode blacked out all similar
portions of the images, revealing only the areas where
Venus’s disks did not coincide. Venus’s parallax could
be seen as two bright crescents, pointing in opposite
directions. Each image pair was fl attened, embedding the
brightness levels of the two parallax crescents into the
pixels of the higher-resolution upper image.Left: Coauthor Richard Smith stands next to his 8-inch Newtonian with which he planned to shoot the transit from his home in West Richland, Wash-
ington. Unfortunately, he eventually took it inside due to continuous overcast skies. Right: During a brief break in the clouds, Smith captured this image
with a 400-mm telephoto lens attached to a Canon 20D DSLR. This image was taken within seconds of Pommier’s image on the facing page.RICHARD SMITH (2)Transit_Experiment.indd 31 6/23/14 12:17 PM