30 September 2014 sky & telescopeAstronomical Experimenting the times of second and third contact from widely
separated locations.
Other amateurs attempted to measure the a.u. with
their own independent observing projects using Hal-
ley’s original method. This required the coordination
of observations between astronomers in widely sepa-
rated locations. Some projects were organized within or
between astronomy clubs. Some were organized over long
distances via the internet. Others were organized between
friends within the amateur community.
The two of us were also eager to emulate astronomers
of prior centuries by taking advantage of the 2012 transit.
Richard would play the role of an 18th-century astronomerremaining in Greenwich or Paris. He would observe a
partial transit from his home in West Richland, Washing-
ton, using his 8-inch f/8 Cave Astrola Newtonian telescope.
Rod would be like Captain Cook, traveling to a Polynesian
island. He journeyed from his home in Portland, Oregon,
to the summit of Haleakala ̄ on the Hawaiian island of
Maui, where the entire transit would be visible and, at an
elevation of 10,000 feet, he’d likely be above any clouds. He
would bring his 8-inch Celestron SCT with an f/6.3 focal
reducer, yielding a focal length of 50 inches
We would each photograph the transit through our
telescope using a Canon 20D DSLR camera. We’d use
Richard’s images to produce a composite image with
a partial transit line and use Rod’s images to produce
a composite image with a complete transit line. After
measuring the parallax angle between the two transit
lines, we’d use the distance between West Richland and
Haleakala ̄ to calculate the distance to Venus and thus the
a.u. Historically, using transit lines has been considered
more accurate than directly measuring Venus’s parallax.
Although Venus has the largest apparent diameter of any
planet, its disk is still quite small, making direct mea-
surement of parallax diffi cult.
On June 5th, Richard awoke to completely overcast
skies. Hoping for improving weather, he set up his
telescope, but there was no change when the transit
began at 3:05 p.m. PDT. At 5:00 p.m., there was still no
improvement and the forecast called for continued clouds.
Richard concluded he would not see the transit at all, so
he took down his telescope and went indoors.Rod Pommier took this image around second contact, clearly
showing the black-drop eff ect. This optical eff ect thwarted eff orts
to measure the a.u. using the transit of Venus since Captain
Cook’s expedition to Tahiti in 1769. The eff ect renders it nearly
impossible to determine the precise moment when Venus makes
internal contact with the Sun’s limb.Left: Coauthor Rod Pommier and his wife SuEllen pose near the summit of Haleakala- on June 5, 2012. Rod brought his 8-inch Celestron SCT, tripod,
wedge, full-aperture solar fi lter, and Canon 20D DSLR to the summit to photograph the entire transit. The Haleakala- Observatory complex is visible
in the background. Right: Pommier took this image of the transit with his SCT. Unlike Smith’s image on the facing page, no clouds are visible.ROD POMMIER (2)Transit_Experiment.indd 30 6/23/14 12:17 PM