The transit, or passage, of Venus across the face of the Sun is one of nature’s rarest celestial phenomena. That was why the planet’s solar crossing on June 8, 2004, shown above, was an eagerly anticipated event. It was the first such transit to be observed in almost 122 years and only the seventh since the invention of the telescope in the 1600s.
Transits of Venus occur in pairs eight years apart. The second event of the pair in the 21st century will take place this year — on Tuesday, June 5, as seen from the Western Hemisphere (Wednesday, June 6, from the Eastern Hemisphere). If you miss this transit, the next one won’t occur until December 11, 2117, or 105 years from now!
[See our Transit of Venus 2012: Complete Coverage Special Report.]
For the planet’s historic, first-in-a-lifetime transit on June 8, 2004, astrophotographers and science journalists Imelda Joson and Edwin Aguirre led two tour groups to Italy. One group was stationed at the Astronomical Observatory of Rome near Monte Porzio (pictured above) while the other was at the Vatican Observatory in Castel Gandolfo.
Edwin Aguirre used a Takahashi FC-60 apochromatic refractor and his trusty Nikon Coolpix 990 digital camera to document Venus’s passage across the Sun’s disk, which lasted six hours from start to finish. Fortunately, the weather over Rome was perfect on Transit Day. Except for a few thin passing clouds, the entire sky remained clear throughout the day.
White-light solar filters were fitted over the main telescope and finder to protect the eye and camera from the Sun’s intense heat and brightness. Unlike a total solar eclipse, where you can remove the filter during totality and safely watch the Sun’s corona with your naked eye, the filters had to be kept securely in place throughout the transit. Other observers brought portable hydrogen-alpha telescopes, the first time such instruments were used on a transit of Venus.
The start of the transit is marked by "first contact," when Venus's small inky disk first touches the Sun's edge and creates an almost imperceptible "dent" on the solar limb. This dent soon becomes more and more pronounced, growing gradually in size as the transit progresses. The view above shows the 2004 transit at the moment of "second contact," when the planet's disk is fully inside the Sun's limb.
Officially known as the Specola Vaticana, the Vatican Observatory is situated within the Papal Palace, on the Alban Hills some 35 kilometers southeast of Rome. The palace, which overlooks the picturesque Lake Albano, serves as the pope's summer residence where he could escape Rome's stifling heat and humidity.
The Vatican Observatory is one of the oldest astronomical research institutes in the world. Its roots date back to the late 1500s, when Pope Gregory XIII appointed a commission to reform the old Julian calendar in use since 46 B.C. (The resulting Gregorian calendar was adopted in 1582 and is our familiar calendar today.) This view shows the papal palace’s inner courtyard and the dome housing a 16-inch Zeiss refractor.
Members of the tour group observed the transit from the spacious roof deck of the Vatican Observatory, which offers a panoramic view of Lake Albano and Castel Gandolfo’s beautiful church dome designed by 17th-century Italian artist Giovanni Lorenzo Bernini.
The June 8, 2004, transit began at 7:20 a.m. local time, when Venus’s disk first touched the southeastern limb of the Sun. It was a very exciting moment — imagine, witnessing an event that had not been seen by human eyes for nearly 122 years! Some members of the group using telescopes fitted with hydrogen-alpha filters were able to see the planet’s silhouette ahead of those using telescopes with white-light filters. Others chose to follow the event on a TV monitor that was hooked up to a video camera at the prime focus of the 16-inch Zeiss refractor.
"Third contact" takes place when Venus's disk touches the other side of the solar limb, signaling the beginning of the end of the transit. The fourth (and final) contact occurs the moment the last traces of the planet's disk disappears from view. The transit is now officially over!
In Italy, information about the 2004 transit of Venus was well disseminated to the public by the local news media and government agencies. This poster was spotted on display at a busy intersection in the town of Frascati, near the Astronomical Observatory of Rome.
After successfully observing the July 11, 2010, total eclipse of the Sun from the Tatakoto Atoll in French Polynesia’s Tuamotu Archipelago, Joson and Aguirre decided to visit the historic Venus Point on Tahiti’s northernmost coast. This was the site where Captain James Cook observed the transit of Venus in 1769. A white concrete monument enclosed in a red fence now marks the spot, which is just a short distance from the Venus Point lighthouse constructed in 1867. Unfortunately, someone stole the plaque on the transit monument in the late 70s or early 80s; perhaps it will be replaced in time for the transit this June.
These series of images, assembled by Aguirre and Joson from their white-light photos in 2004, document the entry, or ingress, of Venus's disk across the Sun (top row) as well as the planet's exit, or egress (bottom row). Aguirre and Joson tried to capture the so-called "black-drop" effect at second and third contacts. In this curious phenomenon, as Venus's silhouette makes internal contact with the limb, it appears to draw a thread of blackness that distorts the silhouette's shape. It's an elusive effect that was first reported by astronomers during the 1761 transit and had thwarted early attempts to measure the times of contacts accurately. Like many observers in their tour groups, Aguirre and Joson didn't see or record the black-drop effect in 2004.
While Joson and Aguirre stood next to the monument, they tried to imagine the hardship and ordeal that Capt. Cook had to endure while sailing from England to Tahiti, and what Tahiti must have looked like in 1769. After 243 years, the transit of Venus will again touch the shores of Venus Point. On June 6, 2012, the planet’s ingress across the solar disk can be viewed shortly after local noon but unfortunately, its egress will not be visible. The Sun would have set that day with the transit still in progress.
Three views of Venus' solar transit in 2004, taken by NASA's sun-observing TRACE spacecraft. The top image is in visible light; the view on bottom left is in the ultraviolet, and the one on bottom right is in the extreme ultraviolet.
Venus transit sky map. [See our Transit of Venus 2012: Complete Coverage Special Report.]