The Transit of Venus

| By Faith Tucker

Image of the last transit taken in Philadelphia on June 8, 2004, by a group of observers including Ted Davis.

Today we have a chance to witness a special moment in history as Venus transits across the disk of the Sun for people across the world to see. This rare astronomical occurrence may have been witnessed by Montezuma in 1520, was first predicted by Johannes Kepler in 1631, launched Captain James Cook’s expedition around the world in 1768, helped us determine the Earth's distance from the Sun in the 1882, and will not occur again until 2117.

The astronomy community is particularly interested in this event because exoplanetsthroughout the Milky Way galaxy regularly transit their parent stars in just the same way. This local example will allow astronomers to test and refine techniques used to determine the composition of these exoplanets' atmospheres, providing insight into whether these distant planets could possibly harbor life.

As Venus begins to cross in front of the disk of the Sun, Venus's atmosphere will refract the Sun's light, illuminating the backlit portion of the planet's atmosphere. Telescopes on the ground and in orbit will be trained on this thin arc of atmosphere lit up by the Sun. Astronomers will use spectrometers to break the light up into its constituent colors, from which they can determine the chemical composition of our over-heated sister planet's atmosphere. Once perfected, this same technique can be used to examine the atmospheres of planets far beyond our own solar system, offering us one of our best clues as to the habitability of these distant worlds.

Not only is this process of discovery exciting for natural science, but it has profound theological ramifications as well. Surely a God capable of orchestrating both the majestic swirls of a spiral galaxy and the intricate language of DNA could bring forth life where and when He chooses, but only now are we on the verge of being able to answer the age-old question: “Did God confine His creative life-giving actions to our own planet, or does His abundant fertility extent far beyond our limited experience?”

In 1882, William Harkness, the Director of the U.S. Naval Observatory, was one of two astronomers to determine from the transit of Venus the distance from Earth to the Sun. Just as previous viewers could never have imagined calibrating the scale of the solar system from such an event, Harkness could not predict its importance in 2004 and 2012 (the most recent Venus transits). As we look to the future, we can hardly imagine what new frontiers the next Venus transit of 2117 will find us exploring.

"We are now on the eve of the second transit of a pair, after which there will be no other till the twenty-first century of our era has dawned upon the earth, and the June flowers are blooming in 2004. . . . What will be the state of science when the next transit season arrives God only knows. Not even our children's children will live to take part in the astronomy of that day. As for ourselves, we have to do with the present ..." ~William Harkness, the Director of the U.S. Naval Observatory, quoted in 1882 (source:

The image above shows Venus on the eastern limb of the Sun during the 2004 transit. As described in Tucker's essay, the faint ring around the planet comes from the scattering of light through its atmosphere, which allows some sunlight to show around the edge of the otherwise dark planetary disk. The faint glow on the disk is an effect of the TRACE telescope through which the image was captured. For more on the historical significance of the transits of Venus (including the voyage of Captain James Cook), see this article from NASA, which also includes links to several live webcasts of today's transit.


About the Author

Faith Tucker

Faith Tucker graduated from Whitman College in Walla Walla, WA in 2011 with Bachelor's degrees in both Astronomy and Religion. At Whitman, she was a student leader of the campus's InterVarsity chapter and gave planetarium shows to students of all ages. Since graduating she has spent time working in astronomy education and public outreach at the NASA Goddard Space Flight Center in Greenbelt, MD and is currently a Project Coordinator for the American Association for the Advancement of Science's program on the Dialogue on Science, Ethics and Religion.


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